Class 8

Haryana State Board HBSE 8th Class Science Solutions Chapter 15 Some Natural Phenomena Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 15 Some Natural Phenomena

HBSE 8th Class Science Some Natural Phenomena Textbook Questions and Answers

Question 1.
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Answer:
(b) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Answer:
(b) becomes positively charged while the cloth has a negative charge.

Question 3.
Write T against true and F against false in the following statements:
(а) Like charges attract each other. (T/F)
(b) A charged glass rod attract a charged plastic straw. (T/F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T/F)
Answer:
(a) False
(b) True
(c) False
(d) False

Question 4.
Sometime, a crackling sound is heard while taking off sweater during winters. Explain.
Answer:
This occurs due to electric discharge between sweater and body. Some energy is always released with electric discharge, which in this case is released in form of a cracking sound.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.
Answer:
When we touch a charged body, it loses its charge, due to process of earthing. Our body is good conductor of electricity and transfers the charges to the earth.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer:
Destructive energy of an earthquake is measured in Ricther Scale. Yes, it will be recorded in this scale. Earthquake with megnitude of 3 on Richter Scale is not much destructive.

Question 7.
Suggest three measures to protect ourselves from lightning.
Answer:
Three measure to stay protected from lightning are:

• Stay indore or under covered area.
• Don’t take bath during lightning.
• We should not use T.V. or phone during lighning.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer:
A charged balloon is atracted by another charged balloon because both carry same charge like charge always repel each other. While the uncharged balloon is attracted by charged balloon due to unlike charged.

Question 9.
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Answer:
An electroscope can be used to detect if a body is charged or not. When the metal strips repel each other proves that the body is charged as repulsion is the sure test to detect if a body carries charge or not.

Question 10.
List three states in India where earthquakes are more likely to strike.
Answer:
Kashmir, Punjab and Gujarat are more prone to earthquake.

Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
We will take following precautions :

• We will try to move to an open space.
• If we are driving, we will slow down the vehicle and move slowly away from that area.
• We will not take shelter under trees or buildings.

Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer:
No, we will not take an umbrella, as this will increase the risk of lighting because wide objects are more prone to lightning strike.

Extended Learning – Activities and Projects

Question 1.
Open a water tap. Adjust the flow so that it forms a thin stream. Charge a refill. Bring it near the water stream. Observe what happens. Write a short report on the activity.
Answer:
For self attempt.

Question 2.
Make your own charge detector. Take a paper strip roughly 10 cm x 3 cm. Give it a shape as shown in Fig. 15.15. Balance it On a needle. Bring a charged body near it. Observe what happens. Write a brief report, explaining its working.
Answer:
For self attempt.

Question 3.
This activity should be performed at night. Go to a room where there is a fluorescent tube light. Charge a balloon. Switch off the tube light so that the room is completely dark. Bring the charged balloon near the tubelight. You should see a faint glow. Move the balloon along the length of the tube and observe how glow changes.
Caution: Do not touch the metal parts of the tube or the wires connecting the tube with the mains.
Answer:
For self Attempt.

Question 4.
Find out if there is an organisation in your area which provides relief to those suffering from natural disaster. Enquire about the type of help they render to the victims of earthquakes. Prepare a brief report on the problems of the earthquake victims.
For more information on these topics, visit:
→ science.howstuffworks.com/lightning.htm
→ science.howstuffworks.com/ earthquake .htm
→ www enchantedlearning.com/subjects/ astronomy/planets/ earth/continents.shtml
Answer:
For self attempt.

HBSE 7th Class Science Some Natural Phenomena Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three natural phenomena.
Answer:
Earthquakes, cyclones, lightning.

Question 2.
According to ancient Greeks who invented thunderbolts?
Answer:
Goddess of Wisdom Minerva.

Question 3.
What are the sparks seen in sky during thunderstorms?
Answer:
Lightning.

Question 4.
Which resin did Greeks knew, produced sparks on rubbing continuously?
Answer:
Amber.

Question 5.
What happens when we rub a plastic scale with our hair?
Answer:
It gets charged.

Question 6.
What happens when charged plastic scale is brought close to bits of paper?
Answer:
Papers get attracted towared scale.

Question 7.
What happens when we rub an inflated balloon and let it free near a wall?
Answer:
Balloon gets attached to the wall.

Question 8.
How many types of charges are gained by rubbing objects?
Answer:
Two.

Question 9.
Name the charges bodies acquire on rubbing.
Answer:
Positive charge and negative charge.

Question 10.
What happens when similar charged bodies are brought close?
Answer:
They repel each other.

Question 11.
What happens when two different charged bodies are brought close?
Answer:
They attract each other.

Question 12.
What will happen when a charged glass rod is brought close to a charged straw?
Answer:
They will attract each other.

Question 13.
What will happen when a charged pen refil is brought close to a charged balloon?
Answer:
They attract each other.

Question 14.
Which charge is conventionally called a positive charge?
Answer:
Charge on a charged glass rod.

Question 15.
A charged glass rod attracts a charged straw. What is the charge on the charged straw?
Answer:
Negative charge.

Question 16.
What is the electric charge generated by rubbing called?
Answer:
Static electricity.

Question 17.
What is the static electricity?
Answer:
Charges which are produced by rubbing and are not movable are called static electricity.

Question 18.
How is electric charges different from static charges?
Answer:
Electric charges can flow but static charges cannot move.

Question 19.
What is used to transfer electrical charges from one body to another?
Answer:
Metallic conductors.

Question 20.
What is the transfer of charges from one body to earth is called?
Answer:
Earthing.

Question 21.
What provision is made in buildings to prevent electrocution?
Answer:
Earthing of wires is done.

Question 22.
How a huge energy is produced during thunderstorm?
Answer:
By repulsion of negative charges from clouds and positive charges from ground.

Question 23.
What is the process of meeting of negative charges from clouds with positive charges from ground to release huge energy called?
Answer:
Electric discharge.

Question 24.
Which place is safe during thunderstorms and lightning?
Answer:
Covered vehicles and buildings.

Question 25.
What should be considered as alert signs to get a safe place during thunderstroms?
Answer:
Hearing thunder without lightning.

Question 26.
Is sitting on a motor-cycle safe during lightning?
Answer:
No.

Question 27.
Where should one take shelter in open during lightning?
Answer:
Under small trees.

Question 28.
Is it safe to use wired phones during lightning?
Answer:
No.

Question 29.
Can a lightning victim electrocute another person?
Answer:
No.

Question 30.
What harms can lightning cause in a lightning victim?
Answer:
Loss of memory, loss of hearing or sight, broken bones etc.

Question 31.
What is the device used to save multistoryed buildings from lightning.
Answer:
Lightning rod.

Question 32.
Where is the lightning rod attached to protect the building from lightning?
Answer:
On the top of the building.

Question 33.
One end of the lightning rod is left loose in the air, where is the other end fixed or attached?
Answer:
Other end of the rod is attached to the ground.

Question 34.
Which fish can give electrical shock?
Answer:
Electrical eel.

Question 35.
What is the capacity of producing electric current in an electrical eel?
Answer:
650 volts.

Short Answer Type Questions

Question 1.
How can charging take place by rubbing?
Answer:
When a plastic comb is rubbed with hair it starts attracting small pieces of paper. Similarly, when two straws are rubbed with polythene and are brought close they repel each Other. Rubbing charges the comb and straws by loading charges on comb and straws, The polythene and hair against which straws and combs are charged also get charged.

Question 2.
How many types of charges do things acquire on rubbing?
Answer:
Charges acquired by objects are of two types named positive charge and negative charge. Charge acquired by a glass rubbed with silk is called positive charge and the charge acquired by the silk is called the negative charge.

Question 3.
How are negative and positive charges related to each other?
Answer:
Positive charges repel each other and negative charges repel each other. In other words similar charges repel each other. On the other hand negative charge is attracted by positive charges or in simple words opposite charges attract each other.

Question 4.
What is static electricity? How is it different from electric current?
Answer:
The electrical charges acquired by bodies on rubbing are called static electricity. These charges are called static because, they cannot move. This is the difference static electricity and electrical current has. Electrical current can move or flow but static electricity cannot move or flow.

Question 5.
What is electrical discharge?
Answer:
Transfer of charges from a body is called electrical discharge. If we touch a charged object, the charge gets transferred to the earth through our body. We say that the object is discharged. This is also called earthing. Electrical discharge can take place between any two conducting bodies.

Question 6.
How electrical discharge takes place in clouds?
Answer:
During thunderstorms the negative charges get accumulated near the clouds and positive charges accumulate near ground. When these negative and positive charges meet, electrical discharge takes place between clouds and grounds. It produces huge amount of energy which is released as lightning and thunder.

Question 7.
How do clouds get charged during thunderstorms?
Answer:
During thunderstorm there is a vigorous movement of air current in upward and downward direction i.e. in opposite direction. This is similar to rubbing of objects, this vigorous movements of water droplets in clouds cause charging of the clouds.

Question 8.
How does lightning strike during thunderstroms?
Answer:
During thunderstorms, the opposite charged clouds and ground come in contact and electrical discharged takes place between clouds and ground and huge energy is released as lightning. This is called lightning strike. Electrical discharge can take place between clouds and ground, clouds and human body, clouds and building etc.

Question 9.
How can we protect ourselves from lightning during thunderstorm when we are out of our home?
Answer:
Following precautions should be used when we are out during thunderstorm:

• We should not stay in open vehicles or places.
• Should not carry unbrella.
• Should not take shelter under tall trees or under poles etc.
• If shelter has to be taken, then it should be taken under smaller trees.

Question 10.
What precautions should we take to secure ourselves from lightning stroke during thunderstorm when we are in our homes?
Answer:
Following precautions should be taken while in house :

• We should not use wired phone.
• Electrical appliances should be plugged off.
• Should not bathe in running water.

Question 11.
Why is it advised to take shelter under smaller trees while in open during thunderstorms?
Answer:
During thunderstorms, we should take shelter under smaller trees because electrical discharge can easily take place with tall trees, so they are easy targets of lightning. While smaller trees are not in reach of lightning often.

Question 12.
How does a lightning rod protect a building from lightning?
Answer:
Lightning rods are installed on the top of the buildings. One end of the rod is left in open and the other one is connected to the earth.When lightning strikes the building, the charges are directly transferred to earth by the rod, this is called earthing. Earthing thus saves the buildings from lightning strike.

Question 13.
Why the Electric Eel is so called?
Answer:
Eel found in South America emits electric discharge from its body. It can produce electric current of 650 volts. It emits discharge to attack its enemies, to give shock to the prey. It can also give shock to human beings too. As these Eels produce electric discharge, they are called electric Eels.

Question 14.
What is an earthquake? How is it measured?
Answer:
Sudden trembling and shaking of the earth is called an earthquake. Due to sudden movements in the uppermost layer of the earth, the earth starts trembling, this movement of earth is called an earthquake. The magnitude of the earthquake is measured through an instrument called seismograph and it is measured on Richter scale.

Long Answer Type Questions

Question 1.
What is static electricity? How many kinds of charges are there?
Answer:
The electrical charge produced due to rubbing of objects is called static electricity. This charge cannot move as the electric current moves. These types of charges are produced only when objects are rubbed. When we rub an inflated balloon with our hair and let it loose, it attaches to wall. This proves that balloon has been charged. Similarly when a glass rod is rubbed with silk, it gets charged.

Charges are of two types : Negative charges and positive charges. Conventionally charge acquired by a glass rod is called positive charges and the charges acquired by the silk with which glass rod is rubbed aquires a negative charge. Similarly charged bodies repel each other and oppositely charged bodies attract each ether.

Question 2.
What is earthing? How is it useful?
Answer:
Transfer of charges to earth through conducting bodies is called earthing. In buildings wiring is done to do earthing when we touch the electric current, it enters the earth through our bodies. The bodies of the living beings including humans are good conductors of electricity. So, they easily acquire charges and transfer them to the earth, if they are in contact of the earth. This is called earthing.

Earthing is very useful as it protects us from electrocution. It prevents electric shocks as it transfers current to the earth. Earthing also saves building from lightning.

Question 3.
How does lightning take place during a thunderstorm?
Answer:
Lightning during thunderstorm takes place due to a phenomenon known as electric discharge. Electric discharge means interaction between oppositely charged objects. During thunderstorms vigorous upward and downward movement of air particles take place. This causes charging of water droplets accumulate in clouds and positive charge accumulates near ground. When these positive charges and negative charges meet a huge amount of energy is released in form of thunder and lightning. This whole process is called electrical discharge.

Question 4.
How can we save ourselves from lightning?
Or
What precautionary measures should be taken to save ourselves from lightning?
Answer:
Lightning gives a warning before appearing. Huge thunder without light is a warning. We should look for a safe place. No place in open is safe.

• One should rush to take shelter in building or house.
• One should not come out of the covered vehicle if on the road.
• One should not keep sitting on open vehicles like scooters, bikes etc.
• One should not take shelter under large and tall trees as they are easy target for electrical discharge.
• One should take shelter under smaller trees while in open as they are not easy target of lightning.
• If in open and no tree or shelter nearabout, one should sit with head folded under arms and embedded between the legs. One should not lie down in open.
• We should plug out all the electrical appliances during lightning.
• We should not use wired telephones during lightning, while mobiles and cordless phones are safe.
• One should not take ones bath during lightning.

Question 5.
What is a lightning rod? How is it used?
Answer:
Lightning rod is a device which is used to save tall buildings from lightning. Tall buildings are easy target to lightning as there can be easy electrical discharge with clouds. Lightning rod is a rod having three spikes on its top and a long earthing- wire to be attached to the earth. The end with spikes is left in open and other end is attached to earth. Lightning rod is fitted on the top of the buildings. During thunderstorm, when electrical discharge takes place between clouds and the building, the lightning rod acquires the charges and transfers them to the earth through its embedded end and saves the buildings from the strike of the lightning.

Question 6.
What is an earthquake? How does it occur?
Answer:
Sudden shaking and trembling of the earth is called earthquake. It occurs due to disturbance deep inside the upper layer of the earth. Earthquake is a natural phenomenon, which can be very devastating depending upon its intensity and magnitude.

The uppermost layer of the earth is not made up of a single flat surface. It is made up of different fragments, called seismic plates. These plates are joined with each other at different points. These plates are always in a continuous motion. Sometimes due to collision of these plates or upward or downward motion of these plates earth starts shaking. This is called an earthquake. The areas falling between these plates are the areas which are the most vulnerable areas for earthquakes. These are called fault zones or in simple language danger zones.

Question 7.
What is a seismograph? How does it work?
Answer:
Seismograph is an instrument which is used to record the intensity of the earthquake. Seismograph has a long rod suspended, with a pen attached to it. A paper is placed under the pen. When an earthquake strikes, the rod starts vibrating. The pen also starts vibrating and paper starts moving under the pen recording the movement of the pen. Scientists further study the seismic waves recorded by pen and make estimates about the intensity of the earthquake. This graph also gives the idea about the energy involved in the earthquake. This idea helps in determining the destructive power of the earthquake.

Some Natural Phenomena Class 8 HBSE Notes

• Natural phenomena like lightning, earthquakes etc. always made people fearful. People had many superstitions regarding these phenomena. They related these phenomenon to wrath and pleasures of Gods.
• Greeks knew that sparks like that of lightning also Occur when amber is rubbed with fur.
• Rubbing the objects with other objects can cause charging like rubbing a plastic scale with hair can charge the scale.
• Similar charged bodies repel each other while oppositely Charged bodies attract each other.
• Charges are of two types : negative and positive.
• Charges on a charged glass rod is said to be positive and other kind of charges are called negative charges.
• Opposite charges attract each other and similar charges repel each other.
• Charges which are generated due to rubbing are called static electricity. Static electricity means where charges do not move as in electric current.
• Charges can be transferred from one body to another. Charges can be transferred from a charged body to earth and this is called earthing.
• Lightning during rain is due to release of huge energy during electric discharge.
• Lightning can be dangerous, but we can secure ourselves by using precautions.
• Lightning rods can protect tall building from lightning as tall objects are easy target for lightning.
• Earthquake is another natural phenomena which can prove disastrous.
• Earthquakes take place due to disturbance in upper crusts of the earth.

Haryana State Board HBSE 8th Class Science Solutions Chapter 17 Stars and the Solar System Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 17 Stars and the Solar System

HBSE 8th Class Science Stars and the Solar System Textbook Questions and Answers

Question 1.
Which of the following is NOT a member of the solar system?
(a) An asteroid
(b) A satellite
(c) A constellation
(d) A comet
Answer:
(c) A constellation

Question 2.
Which of the following is NOT a planet of the sun?
(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth
Answer:
(a) Sirius

Question 3.
Phases of the moon occur because:
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
Answer:
(c) the shadow of the Earth covers only a part of the moon’s surface.

Question 4.
Fill in the blanks :
(a) The planet which is farthest from the Sun is __________.
(b) The planet which appears reddish in colour is __________.
(c) A group of stars that appear to form a pattern in the sky is known as a __________.
(d) A celestial body that revolves around a planet is known as __________.
(e) Shooting stars are actually not __________.
(f) Asteroids are found between the orbits of __________ and __________.
Answer:
(a) Neptune
(b) Mars
(c) constellation
(d) Satellite
(e) Meteors
(f) Mars and Jupiter.

Question 5.
Mark the following statements as true (T) or false (F) :
(а) Pole star is a member of the solar system. ( )
(b) Mercury is the smallest planet of the solar system ( )
(c) Uranus is the farthest planet in our solar system. ( )
(d) INSAT is an artificial satellite. ( )
(e) There are nine planets in our solar system. ( )
(f) Constellation Orion can be seen only with the telescope. ( )
Answer:
(a) False
(b) False
(c) False
(d) True
(c) False
(f) False

Question 6.
Match items in Column A with one or more items of Column B :

Answer:

Question 7.
In which part of the sky can you find Venus if it is visible as an evening star?
Answer:
In western sky.

Question 8.
Name the largest planet of the solar system.
Answer:
Jupiter.

Question 9.
What is a constellation? Name any two constellations.
Answer:
A group of stars in a recognizible shape is called a constillation. Orion and the Great Bear are constellations.

Question 10.
Draw sketches to show the relative positions of prominent stars in (i) Ursa Major and (ii) Orion.
Answer:

Question 11.
Name two objects other than planets which are members of the solar system.
Answer:
Meteors and Asteroids.

Question 12.
Explain how you can locate the Pole Star with the help of Ursa Major.
Answer:
Pole star is situated at the end of the Ursa Major. If a straight line starting from the last two stars is extended towards the north direction, it will lead to the Pole Star.

Question 13.
Do all the stars in the sky move? Explain.
Answer:
All the stars in the sky do not move, but they appear to move from east to west. This is actually due to rotation of earth on its axis. Earth moves from west to east. So it appears as the stars are rising from east and as the day dawns they sets in the west.

Question 14.
Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the earth?
Answer:
Stars are away from the earth millions of kilometres away. It is not convenient to express such a large distance in the units of km. So the distance of stars from the earth is expressed in time taken by light to travel in one year. Eight light years mean time taken by light to travel in eight years.

Question 15.
Boojho made the following sketch (figure) of the solar system. Is the sketch correct? If not, correct it.
Answer:
No, the sketch is incorrect. The following sketch is correct.

Extended Learning – Activities and Projects

Question 1.
If possible, visit a planetarium. There are planetariums in many cities. In a planetarium you can see the motion of the stars, constellations and planets on a large dome.
Answer:
For self attempt.

Question 2.
On a moonless night observe the sky for a few hours. Look out for a meteor, which appears as a streak of light. September-November is a good time for observing meteors.
Answer:
For self attempt.

Question 3.
Learn to identify the planets visible to the naked eye and some prominent constellations such as Great Bear (Saptarshi) and Orion. Also try to locate the Pole Star and the star Sirius.
Answer:
For self attempt.

Question 4.
Select a convenient place on the roof of your house or in some playground from where you can watch sunrise clearly. Remember that you will have to do this activity for a few months. So, choose the place carefully. On a sheet of chart paper draw the outline of the eastern horizon indicating big trees, poles, etc. Mark the outline of the sheet so that you can place it in the same position every time. After every two weeks, note the position from where the Sun rises and mark this on your chart paper (Fig.). Also note the date of your observation. Repeat this for a few months. It is advisable that you start observations in the month of November or May.

Does the Sun always rise from the same direction? Discuss your observations with you teacher, parents and elderly people in your family or in the neighbourhood.
Answer:
For self attempt.

Question 5.
Form a group of studens. Prepare a model of the solar system showing the planets, and their relative sizes. For this take a large chart paper. Make spheres representing different planets according in their relative size (Use Table). You may use newspaper, clay or plasticine to make spheres. You can cover these spheres with paper of different colours. Exhibit your model in the class.

Answer:
For self attempt.

Question 6.
Try to make a scale model of the solar system showing distances of the planets from the Sun (Use Table 17.1). Did you face any difficulty? Explain it.
Answer:
For self attempt.

Question 7.
Solve the following riddle and try to make similar riddles yourself:
My first is in VAN but not in PAN
My second is in EARTH and also in HEAVEN
My third is in ONE and not in TWO
My fourth is in BUN and also in FUN
My last is in STAR but not in RADAR
I am a planet that moves round the Sun.
You can read more on the following websites:
→ http://www.nineplanets.org
→ http://www.kidsastronomy.com
→ http://www.solarsystem.nasa.gov/planets
→ http://aa.usno.navy.mil/fazz/does/moon- phases.html
Answer:
For self attempt.

HBSE 7th Class Science Stars and the Solar System Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name any three celestial bodies.
Answer:
Stars, Satellite, Planets.

Question 2.
Name the planets of solar system which cannot be seen by naked eye?
Answer:
Neptune and Pluto.

Question 3.
Name the force which makes planets move around the sun.
Answer:
Gravitational force.

Question 4.
Which has higher density : Earth or Sun?
Answer:
Earth.

Question 5.
Name the planet narest to earth.
Answer:
Mars is nearest to earth.

Question 6.
Write the names of any two constellation.
Answer:
Great Bear and Orion.

Question 7.
A group of stars visible in winter season look like a cluster of twinkling gems.
Answer:
Pleiades constellation.

Question 8.
In which season of the year are the constellations scorpio and orion visible in the Northern Hemisphere?
Answer:
Orion – Winters.
Scorpio – Summers.

Question 9.
Define star.
Answer:
Stars are the heavenly bodies that are extremely hot and have light of their own.

Question 10.
Name the star which is nearest to the earth.
Answer:
Alpha Centuari.

Question 11.
Write the names of two planets which are closer to the sun than the earth.
Answer:
Mercury and Venus.

Question 12.
Name the planet nearst to the sun.
Answer:
Mercury.

Question 13.
Name the planet farthest from the sun.
Answer:
Neptune.

Question 14.
Which planet of the solar system is the hotest?
Answer:
Mercury.

Question 15.
Name the planet of the solar system Which is nearer to the Sun and Venus.
Answer:
Mercury.

Question 16.
Which planet in the solar system is nearest to the earth?
Answer:
Venus.

Question 17.
Name the planet, where there is no carbon dioxide.
Answer:
Mercury.

Question 18.
Name the planets, which has no moon?
Answer:
Mercury and Venus.

Question 19.
Give any two applications of remote sensing.
Answer:
(i) Preparing waste land maps.
(ii) Survey for ground water and mineral resources.

Question 20.
A constellation having seven prominent stars, is visible during the winter. Name the constellation.
Answer:
Orion.

Question 21.
A belt of assorted debris, which failed to assemble into a planet, is located between the orbits of two planets in the solar system. Name these two planets.
Answer:
Mars and Jupiter.

Question 22.
Which planet has rings around it?
Answer:
Saturn.

Question 23.
Name largest asteroid.
Answer:
Ceres.

Question 24.
Why do meteors shine?
Answer:
On entering earth’s atmosphere, meteors become hot and bum due to friction of earths atmosphere and start to shine.

Question 25.
What are meteorites?
Answer:
Big pieces of rock material which do not bum completely in atmosphere of earth, fall on its surface. These are called meteorites.

Question 26.
How are comets formed?
Answer:
When the path of objects near the edge of solar system is disturbed to push them near to sun, comets are formed.

Question 27.
After how much time Halley’s comet is seen?
Answer:
After every 76 years.

Question 28.
Why does pole star appear to be stationary?
Answer:
Pole star lies on the axis of rotation of earth and appears stationary when viewed from any part of earth.

Question 29.
What does the colour of a star signify?
Answer:
Colour of a star signifies its temperature.

Question 30.
Define a satellite.
Answer:
A satellite is a solid heavenly small sized body revolving round a planet.

Short Answer Type Questions

Question 1.
Distinguish between stars and planets.
Answer:

Question 2.
Explain the importance of stars for the people in ancient times.
Answer:
In ancient times when there were no compass, night sky was very useful in finding the direction. As pole star remains fix in the sky in north, it indicated north direction. As the stars change their position with time, it has been possible to find the time with relative position of stars.

Question 3.
How is the pole star located in the sky? Why is it so special?
Answer:
The earth rotates on its axis from west to east, therefore, the stars appear to move in opposite direction, i.e. east to west. But pole star lies on the axis of rotation of earth which is fixed, Therefore, pole star also seems to be fixed in the sky. It is always in north direction and is very useful for finding direction.

Question 4.
Distinguish between star and shooting star.
Answer:

Question 5.
What is a meteor? Why does it last for a very short time?
Answer:
Meteors are the heavenly bodies made of rocky material which enter earth’s atmosphere. When they travel through air they become hot and burn because of friction. Due to this, these rocky pieces melt and vaporises very fast and do not last long.

Question 6.
Distinguish between natural and artificial satellites.
Answer:
Natural satellites are far away from planets. They are comparatively larger in size and are present naturally. Artificial satellites are sent from earth with specific requirements. Their distanc, size and mass are lesser than the natural satellite.

Question 7.
What is solar system? Name the planets situated between the sun and the earth?
Answer:
The solar system consists of the sun, eight planets; and their satellites and other heavenly bodies like meteors, comets and asteroids. The sun is the centre of the solar system and all the planets revolve around the sun in elliptical paths called orbits. The planets situated between the sun and the earth are Mercury and Venus.

Question 8.
What are the phases of the Moon?
Answer:
Moon has no light of its own. It reflects light of the Sun falling on it. On new moon day, moon is between the sun and the earth and no reflected light from it reaches the earth. We cannot see moon on that day. The visible moon increases every day till fifteenth day from the new moon day, the full phase of the moon is visible.

Positions of the Moon in its orbit and its corresponding phases
So, the waxing and waning of moon periodically as it revolves around the earth is called phases of moon.

Question 9.
Why moon cannot be used as a communication satellite?
Answer:
Moon is a natural satellite of the earth but it cannot be used as a communication satellite because :

• It is very far away from earth.
• Its time period 27.3 days is too large.
• It has neither equitorial orbit nor polar orbit which makes a satellite useful for different purposes.

Question 10.
What are constellations? Name some easily recognizible constellations in the sky.
Answer:
Group of stars forming a recognizible shape is called a constellation. These group of stars are identified in different shapes. Constellations do not change their shape. They also appear to move from east to west as other stars appear to. Some major constellations are Ursa Major, Ursa Minor, Orion, Cassiopeia etc. Some of them are visible during summers while some are visible during winters.

Question 11.
What are various types of motions associated with the planet earth?
Answer:
The earth has four types of motion. These are :

(i) The earth’s daily rotation on its axis.
(ii) The earth’s annual revolution around the sun.
(iii) The earth’s precession (conical motion of earth’s axis).
(iv) As a part of solar system, the earth’s motion in space along with the sun.

Question 12.
Explain the constellation Ursa Major.
Answer:
Ursa Major is one of the most famous constellation. We can see this constellation during summers. It is also called the Great Bear or the Saptarishi. There are seven prominently shining stars in this constellation which are arranged in shape of a question mark. At the tail of this constellation lies the Pole Star.

Question 13.
Describe the constellation also called the hunt.
Answer:
A well known constellation named Orion is also called the hunter. This constellation can be seen in the late evenings of winter. It has seven or eight brightly shining stars arranged in shape recognized with hunter. The brightest star in the sky Sirius is located at the extended line from the tail of this constellation.

Question 14.
What are asteroids?
Answer:
Asteroids are the small objects which revolve around the sun in a large gap between the orbits of Mars and Jupiter. These are quite large in their number and are considered as the part of our solar system. Each asteroid has its own orbit.

Question 15.
What are comets?
Answer:
Comets are the part of our solar system which revolve around the sun in highly elliptical orbits. It appears with a bright head and a long tail. The length of the tail grows in size as it approaches the sun. The tail is always directed away from sun.

Question 16.
What are various superstitions connected with appearance of comets?
Answer:
They are considered to be the messangers of destruction and disasters. They are supposed to bring wars,epidemics and flood with them. So, their appearance is considered as unauspicious.

Question 17.
List five uses of artificial satellites.
Answer:

• Weather forecasting.
• Radio and television transmission.
• Long distance communication.
• Locating mineral resources.
• Gathering information about our space.

Long Answer Type Questions

Question 1.
Explain celestial sphere.
Answer:
The large imaginary sphere on which all the heavenly bodies like stars, planets and satellites seems to lie is known as celestial sphere. Since we are on the earth, the earth appears stationary to us. When we look at the sky, the various objects in the sky like the stars and the moon appear to be moving round the earth. In other words, the celestial sphere appears to be moving from east to west round the earth. This apparent motion of the celestial sphere from east to west is actually due to the daily rotation of the earth from west to east. Since the earth rotates from west to east, the celestial sphere appears to rotate in the opposite direction, from east to west.

Question 2.
What are constellations? Explain. Name some prominent constellations with their Indian names.
Answer:
The groups of stars which seem to be arranged in the sky in beautiful patterns and recogniseable shapes are known as constellations. With each constellation, the ancient astronomers assigned the name of an object which it appears to resemble. There are 88 constellations into which the whole of the sky has been divided. In Indian astronomy, the constellations are known as Nakshatras.

Some prominent constellations with their Indian names are given below :
(i) Ursa Major or Saptarishi.
(ii) Ursa Minor or Laghu Saptarishi
(iii) Orion or Mriga or Vyadha
(iv) Tarus or Vrashba
(v) Scorpio or Vrishchika.

Question 3.
What is pole star? What is specific j about its position in the sky?
Answer:
There is only one star in the sky which appears stationary to an observer on earth. This star is named as pole star (Polaris) or Dhruvtara in India. This star appears stationary because, i it lies in the direction of the axis of the Earth about which the earth rotates. Any point on or j along the axis of a rotating body appears to be stationary. So, the pole star that lies along the direction of the axis of rotation of the earth, always sppears to be stationary.

Question 4.
What are artificial satellites? Explain their usage.
Answer:
Man made objects orbitting in outer space around the earth or any other planet are called artificial satellites of earth or that particular planet. The satellite like INSAT 3E or Kalpana Chawla I are examples of artificial satellites. Artificial satellites have many practical applications that effect our lives in many ways, i Long distance transmission of television programmes, communication through telephones and internet could be possible because of them. Artificial satellites are also used for research, defence and remote sensing. Remote sensing means collecting information from a distance. Information is collected regarding weather, agriculture, land and ocean features including movement of fish.

 Stars and the Solar System Class 8 HBSE Notes

• We can see many celestial bodies in a clear night sky.
• Stars are one of the celestial bodies which emit light of their own.
• Sun is also one of the stars which emits light and is a great source of heat. It is the closest star which is the centre of our solar system.
• Stars are many light years away from the earth and thus look very small from earth.
• Stars appear to travel from east to west.
• Pole star is the most shining star in the night sky. The pole star appears to.be stationary. It is situated near axis of rotation of earth and is thus helpful in finding direction.
• A group of stars, appearing in different shapes are called constellations. Their shapes resemble different objects and thus are named after the names of the objects.
• Other improtant parts of night sky are the planets. Planets are those celestial bodies, which revolve around sun.
• Our solar system consists of eight planets revolving around sun. It also consists of many other celestial bodies like asteroids, comets and meteors.
• Comets are the celestial bodies that revolve in highly elliptical orbits around sun.
• Bright streak of light in a night sky are commonly called shooting stars or meteors.
• A celestial body revolving around another celestial body is called a satellite.
• Artificially sent bodies in space, which revolve around earth or any other planet or a natural satellite is called an artificial satellite
• Jupiter is the largest planet while Venus is brightest planet in the night sky.
• Moon is the natural satellite of the earth. Moon appears in different phases. The phases of Moon occur because we can see only that part of the moon which reflects light towards us.

Haryana State Board HBSE 8th Class Science Solutions Chapter 10 Reaching the Age of Adolescence Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 10 Reaching the Age of Adolescence

HBSE 8th Class Science Reaching the Age of Adolescence Textbook Questions and Answers

Question 1.
What is the term used for secretions of endocrine glands responsible for changes taking place in the body?
Answer:
Hormones.

Question 2.
Define adolescence.
Answer:
Adolescence: The period of life, when the body undergoes changes, leading to reproductive maturity is called adolescence.

Question 3.
What is menstruation? Explain.
Answer:
When egg produced by ovary does not get fertilized, it along with the thickened lining of the uterus and blood vessels get flown off out of the body every month as bleeding in women. This is called menstruation.

Question 4.
List the changes in the body that take place at puberty.
Answer:
Certain changes take place in the bodies of boys and girls at age of puberty. These include:
(i) Growing of hair at different body parts
(ii) Sudden increase in height.
(iii) Growth of moustaches and beards in boys.
(iv) Voice,of boys get coarsed.
(v) Development of breast in girls and hips get heavy.
(vi) Development of sex organs.

Question 5.
Prepare a table having two columns depicting names of endocrine glands and hormones secreted by them.
Answer:

Question 6.
What are sex hormones? Why are they named so? State their function.
Answer:
Hormones which constitute the secondary sexual characters are called sex hormones. They are called sex hormones because it is because of them that sex is diferentiated i.e. a boy is distinguished from a girl due to these hormones. Their function is to develop the secondary sexual characters in boys and girls.

Question 7.
Choose the correct option:
(a) Adolescents should be careful about what they eat, because ………….
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
Answer:
(ii) proper diet is needed for the rapid growth taking place in their body.

(b) Reproductive age in women starts when their …………..
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
Answer:
(i) menstruation starts.

(c) The right meal for adolescents consists of …………
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
Answer:
(ii) chapati, dal, vegetables.

Question 8.
Write notes on:
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
Answer:
(a) Adam’s Apple:
Adam’s apple is a protruding part in the throat. It is the enlarged voice box or larynx, which gets enlarged at the onset of puberty. This makes the voice of the boys hoarse.

(b) Secondary Sexual Characters are the characters which distinguish a boy from a girl. Characters like hair on chest, under the arms, development of breast, beard and moustaches etc. are all called secondary sexual characters.

(c) Sex determination in unborn baby: The sex of the unborn baby is determined by the sex chromosomes of the father. An unfertilized
egg always have X chromosome. If a sperm contributes X chromosome then the baby will be a female and if the sperm contributes Y chromosome, the baby will be a male. So it is the father, who is responsible for the sex of the unbomhaby.

Question 9.
Word game: Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone 10. Female hormone

Down
1. Male hormone
2. Secretes thyroxine
3. Another term for Teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence

Answer:

Question 10.
The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Answer:
We conclude that girl are taller than boys age of 12 yr. generally and there height is same at the age of 16 years but some boys gain height and generally become taller then girls.

Extended Learning – Activities And Projects

1. Find out from your elder relatives about their awareness of the leagal status of early marriage. You yourself may get information on it from your teacher, parents, a doctor or the internet. Write a two-minute speech explaining why early marriage is not good for the couple.
Answer:
The legal marriagable age for girls is 18 years and for boys it is 21 years. Before this age marriage is considered a crime. Early marriage is not good for couples because they are not prepared physically and mentally for the responsibilities of married life. A girl attains sexual maturity at age of about eighteen years. Before that her resproductive system is not fully prepared to bear a baby. Similarly boys are not capable of running the household as most of the boys at this age are pursuing their studies. So, the boys and girls should attain physical and mental maturity before getting married.

2. Collect newspaper cuttings and information in magazines about HIV/AIDS. Write a one page article of 15 to 20 sentences on HIV/AIDS.
Answer:
HIV/AIDS is a sexually transmitted diseased (STD) that means this diseases mostly spreads by sexual contacts with an HIV/AIDS infected persons. AIDS stands for Acquired Immunodeficiency Syndrome. It is created by HIV virus. This disease is a fatal disease for which no permanent treatement has been deviced by the scientists. AIDS is actually a disease which destroys the patients immune system slowly. The damage is most of the time permanent and beyond repair. Due to weak immunity the patient easily fall prey to many diseases which eventually kill the person.

Prevention is the only cure for HIV/AIDS. It is advised that one should maintain sexual hygiene and practice safe sexual relationship with a single partner.

3. In our country, according to a census, there are 882 adolescent femals for every 1000 males. Find out:
(a) the concerns of the community regarding this low ratio. Remember that the chance of having a boy or a girl is equal.
(b) what amniocentesis is and how useful this technique is. Why, is its use for indentification of sex of the unborn child banned in India l
Answer:
(a) The society is quite concerned about this issue. This is going to create a problem for them in future as it will become difficult for the boys to find girls for marriage.

(b) It is used to see, if all the organs of a feotus are developing well. It is banned in India to use this technique to determine the sex of the unborn child because they kill the female feotus to have baby boys in future. This is called female feoticide. The female feoticide has disturbed the ratio of boys and girls in India.

4. Put your ideas together and write a short note on the importance of knowing facts about reproduction.
For more information , visit:

• www.teenshealth.org/teen/sexual_health/
• www.ama_assn.org/ama/pub/category/ 1947.html
• www.adolescenthealth.com

Answer:
It is important to know facts about reproduction, because this phase i.e. reproduction phase has to come in every bodies life. It will help to handle all the physical and mental changes coming with sexual maturity in the bodies. It will also help in deciding one’s own course of life in future and save for many STDs.

HBSE 8th Class Science Reaching the Age of Adolescence Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is the phase of life when the body undergoes changes to attain reproductive maturity called?
Answer:
Adolescence.

Question 2.
What is the age period of adolescence?
Answer:
13 years to 18 years.

Question 3.
What is reproductive maturity called?
Answer:
Puberty.

Question 4.
Write any two changes in bodies of boys during adolescence.
Answer:
Increase in height, hairy line above lips.

Question 5.
What makes a person tall during adolescence?
Answer:
Elongated long bones of arms and legs.

Question 6.
What happens to voice box at puberty?
Answer:
It begins to grow.

Question 7.
What is the protruding part of the larynx visible in boy’s throat called?
Answer:
Adam’s Apple.

Question 8.
What changes occur in the voice of boy’s at the onset of puberty?
Answer:
It becomes hoarse.

Question 9.
Why do growing boys and girls get acnes or pimples?
Answer:
Due to increased secretions of sebacious glands.

Question 10.
What are those characters called, which distinguish a boy from a girl?
Answer:
Secondary sexual characters.

Question 11.
Give any one secondary sexual character of boys.
Answer:
Growth of moustaches and beard.

Question 12.
Give any one secondary sexual character of girls.
Answer:
Growth of breasts.

Question 13.
What controls the body changes during adolescence?
Answer:
Hormones.

Question 14.
What are hormones?
Answer:
Hormones are the chemical substances secreted by Endocrine glands.

Question 15.
Name the hormones secreted by testes.
Answer:
Testosterone.

Question 16.
Which hormone is secreted by ovaries 7
Answer:
Estrogen.

Question 17.
Which endocrine gland is called the master gland?
Answer:
Pituitary gland.

Question 18.
What are hormones secreted by testes and ovaries called collectively?
Answer:
Sex hormones.

Question 19.
Name the sex hormones secreted by testes and ovaries.
Answer:
Testosterone and Estrogen.

Question 20.
Name any one hormone secreted by Pituitary gland.
Answer:
Follicle stimulating Hormone or FSH.

Question 21.
Which hormone is responsible for the maturity of ova or sperms?
Answer:
Follicle stimulating hormone.

Question 22.
What is the common name given to ova and sperms?
Answer:
Gametes.

Question 23.
What is the beginning of menstruation called?
Answer:
Menarche.

Question 24.
What is the stoppage of menstruation called?
Answer:
Menopause.

Question 25.
What are the names given to sex chromosomes?
Answer:
X and Y.

Question 26.
Which sex chromosome determines the sex of body?
Answer:
Y Chromosome.

Question 27.
Which hormone is secreted by thyroid?
Answer:
Thyroxin.

Question 28.
Which hormone is secreted by pancreas?
Answer:
Insulin.

Question 29.
Which hormone controls the blood sugar level?
Answer:
Insulin.

Question 30.
Which hormone is secreted by Adrenal glands?
Answer:
Adrenalin.

Question 31.
Which hormone is called stress hormone?
Answer:
Adrenalin.

Question 32.
Why adrenalin is called stress hormone?
Answer:
Adrenalin is called stress hormone because it helps to calm down when one is angry.

Question 33.
What is a balanced diet?
Answer:
Diet containing all the necessary minerals in right proportion is called a balanced diet.

Question 34.
Name any food, which is called a balanced food in itself.
Answer:
Milk.

Question 35.
Which virus causes AIDS?
Answer:
HIV.

Short Answer Type Questions

Question 1.
What is adolescence?
Answer:
The phase of a person’s life, when his body undergoes changes to attain reproductive maturity is called adolescence. Adolescence begins at the age of 13 and lasts till the age of 18 or 19 years.

Question 2.
What are the signs of adolescence?
Answer:
Certain body changes mark the onset of puberty. Hairy line above lips in boys and sudden increase in height are the signs of puberty. In girls developing breasts show the on set of puberty.

Question 3.
Why some boys or girls have improportionate body parts during adolescence 7
Answer:
Some times the boys and girls have improportionate body parts. They look tall but face look smaller or other tilings. This is because all body parts do not grow at the same rate. But slowly they all catch up and body becomes balanced.

Question 4.
What changes take place in the body of adolescents during this period?
Answer:
Many changes take place in the bodies of boys and girls during adolescence. Their shoulders become wider and chest becomes broader. Girls get developed breasts and their hips become wider. Muscles of boys grow more than the girls.

Question 5.
What changes occur in the voice of boys and girls during puberty?
Answer:
The voice box or the larynx begins to grow. Boys have more grown voice box. It can be seen as the protrubed part in their throat.
Their voice becomes deep and sometimes, it grows more than controlled limit and their voice become hoarse. Girls get a high pitched voice.

Question 6.
What causes the changes in human body during puberty?
Answer:
The changes which occur during puberty are caused due to some chemical substances secreted by glands. These chemical substances are acalled Hormones. Endocrine system in human body has various glands, which secrete many important hormones which help the body to grow and mature.

Question 7.
How do sex hormones work in human body?
Answer:
In males the testosterone is secreted by testes and it causes growth of moustaches and beard. In girls estrogefi causes the development of mammary glands . They develop inside the breast and cause enlargement of breasts.

Question 8.
How does pituitary gland initiate the puberty in humans?
Answer:
Pituitary gland is called the master gland. It stimulates the testes and ovaries to produce sex hormones i.e. Testosterone and estrogen. These sex hormones further initiate the changes in body to attain sexual maturity.

Question 9.
What is menstruation?
Answer:
Monthly bleeding in women is called menstruation, when egg is matured and released by ovaries. It if not fertilized is dispelled by body along with the thick lining of uterus and with blood vessels. It is released from the body in form of monthly bleeding. It is called menstruation.

Question 10.
How the sex of the body is determined?
Answer:
Every human beings have 23 pairs of chromosomes in the nuclei of their cells. A pair of sex hormones are also among them. Females have XX sex chromosomes and males have XY sex chromosomes, when after fertilization the zygote get both X chromosomes from male and female, it will develop into a baby girl. When the zygote get X chromosome from female and Y from male, then it develops into a male. Thus the chromosome from a male decides if a baby will be a male or a female.

Long Answer Type Questions

Question 1.
What changes occur in body during puberty?
Answer:
Various changes occur in the body of human beings during puberty. These changes occur due to hormones secreted by reproductive organs. These changes are the following:
(a) Physical changes:
Various changes occur in the bodies of boys and girls. Boys get broader shoulders and wider chest. Sudden increase in their height is accompanied by growth of hair on their body parts. They get moustaches and beard.Girls get developed breasts and wider hips. More secretions from sweat and oil glands cause pimples and acnes in some young people.

(b) Change in Voice:
Voice of boys become deep due to enlarged larynx. Some time more growth in voice box is visible as Adam’s Apple in their throats. Their voice becomes even coarse in case of extra growth of larynx. Voice of girls become high pitched.

(c) Development of Sex Organs:
The reproductive organs of boys and girls become active. Testes start producing sperms and ovaries release matured eggs. Mental and Emotional Maturity: Young people become more mature mentally, emotionally and intellectually.

Question 2.
How are the changes of adolesence controlled by hormones?
Answer:
The endocrine system of body secretes many chemical substances which are directly poured into the blood stream, these chemical substances are called hormones. All changes taking place during adolescence are controlled by these hormones.

Pituitary glands secrete growth hormones which stimulates the sex organs to release hormones.. Testes start secreting testosterone and ovaries start secreting estrogen. These sex hormones cause secondary sexual characters. Estrogen causes development of mammary glands which develop under breast, thus breast starts enlarging in females.

Question 3.
How can bad habits like Drug addiction harm the young people?
Answer:
Boys and girls feel a little bit insecure and confused during adolescence due to sudden changes in their bodies. This can mislead them to certain unhealthy and immoral habbits, like drug addiction and many others. Drug addiction is a very bad habit which can spoil our lives. It is easy to start, taking drugs but very difficult to shun this habit. Drugs can cause many long term harms on our bodies.

They make our body weak and prone to many communicable diseases like AIDS and many other sexual disorders. AIDS virus HIV can pass on to a healthy person from an infected person by sharing the infected syringe. The drug addicts inject drugs by using syringe. The same syringe is shared by other addicts also, so the infected syringe can spread AIDS to others also.

Question 4.
Who is responsible to determine the sex of unborn baby: Father or mother?
Answer:
Each human being have 23 pairs of chromosomes in the nuclei of every cell. These chromosomes contain the hereditary information. Out of these chromosomes a pair of chromosome are called sex chromosomes, which are named X and Y Chromosomes. Each female has 2 X chromosomes while the males have one X chromosome and one Y chromosome. The unfertilized egg released by ovaries always have one X chromosome. Testes produce some sperms with X chromosome and some with Y chromosome.

If sperms with X chromosome fertilize with egg with unborn is a female, but if the sperms with Y chromosome fertilizes with egg, then the unborn baby will be a male. So, it becomes clear that it is the sperm released by father carrying X or Y chromosomes, that determines the sex of the unborn baby.

Question 5.
What should be done to maintain reproductive health?
Answer:
Following measures can help the young people to maintain their reproductive health.
(i) Balanced Diet:
Diet is very important for a growing body. Diet should be a balanced diet. Balanced diet contains all the necessary elements in required proportion. Elements like carbohydrates, proteins, fats and vitamins should be integral part of a balanced diet. Milk provides all the required elements in required proportion. Junk and fast food are good to taste but they are not nutritious so they should not be included in diet.

(b) Personal Hygiene:
One should keep one’s body clean by bathing everyday. All parts of the body should be washed properly because infections can take place due to more sweat and oil secretion by sweat and oil glands.

(c) Physical Exercise:
Daily routine of physical exercise can keep body fit and circulation of blood gets maintained providing energy to all parts of the body.

Reaching the Age of Adolescence Class 8 HBSE Notes

1. A baby becomes adult after passing a few development stages.
2. The age at which a child becomes capable of reproduction is called adolescence.
3. At the age of 11 years to 19 years a child reaches puberty.
4. Reproductive organs start developing as the puberty sets in.
5. Various changes occur in the bodies of boys and girls at age of puberty. Hair starts growing at different parts of body. Girls have developed breasts, heavy hips, boys get.moustaches and beard, their voice become heavy.
6. Height gain is prominent at age of puberty along with other changes. Hormones starts taking control of the reproductive organs, and make the beginning of maturity of reproductive organs.
7. Hormones are the chemical substances which are secreted by the pituitary glands directly into the blood stream.
8. Growth hormones stimulate other glands to secrete various other hormones to control various other body functions.
9. Various hormones secreted by different glands perform various functions. Ovaries and testes secrete hormones for sexual maturity, pancreas secrete Insulin to control sugar level, thyroid secret thyroxin and adrenal glands produce adrenalin. All these hormones are necessary for proper growth and development of body.
11. With onset of puberty females have hormones like estrogen. They have their uterine wall prepared to receive the fertilized egg. They have another phenomenon called menstruation. In this phenomenon they get the unfertilized egg flown out of body through blood.
12. Reproductive health needs a lot of care and one needs to maintain hygiene and physical activity.
13. Proper nutrition and balanced diet in necessary for growing body, so it should be taken care of.

Haryana State Board HBSE 8th Class Science Solutions Chapter 11 Force and Pressure Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 11 Force and Pressure

HBSE 8th Class Science Force and Pressure Textbook Questions and Answers

Question 1.
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer:
(i) We push the door to open it.
(ii) We pull the desk to change its position.

Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:
When we apply force on clay with our fingers, its shape gets changed, when we press balloon with our hands, its shape get changed.

Question 3.
Fill in the blanks in the following statements :
(a) To draw water from a well we have to _________ at the rope.
(b) A charged body _________ an uncharged body towards it.
(c) To move a loaded trolley we have to _________ it.
(d) The north pole of a magnet _________ the north pole of another magnet.
Answer:
(a) pull
(b) attracts
(c) push it
(d) repels.

Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the followiong terms:
muscular, contact, non-contact, gravity, friction, shape, attraction
(a) To stretch the bow, the archer applies a force that causes a change in its _________
(b) The force applied by the archer to stretch the bow is an example of _________ force.
(c) The type offeree responsible for a change in the state of motion of the arrow is an example of a _________ force.
(d) While the arrow moves towards its target, the forces acting on it are due to _________ and that due to _________ of air.
Answer:
(a) shape
(b) muscular
(c) contact
(d) gravity and friction.

Question 5.
In the following situations identify the agent exerting a force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer:
(a) Agent are fingers, object is lemon, effect of force can be observable in form of lemon juice being expelled by squeezing.

(b) Agent is hand of the person squeezing the tube, object is toothpaste tube and effect of the force can be observed’ as the paste coming out of the tube.

(c) Agent is the load suspended, object is the spring and effect can be seen in the form of elongation of spring on suspension of load.

Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
The force due to hammering causes the change in the shape of the iron and iron can be moulded in the shape of the required tool.

Question 7.
An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for, the attraction between the balloon and the wall?
Answer:
Electrostatic force.

Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer:
Forces acting on the plastic bucket are the muscular force and gravitational force. The forces do not bring the change in its state of motion because they are acting in opposite direction with equal magnitude. The effect of the gravitational force will pull it down if the muscular force will grow weak. The body will feel the stretch of gravitational force and will have to bend” to cancel the magnitude of gravitational force.

Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer:
Gravitational force and frictional force.

Question 10.
When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper.
The rise of water in the dropper is due to
(a) pressure of water
(b) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure
Answer:
(d) atmospheric pressure.

Extended Learning – Activities and Projects

Question 1.
Make a 50 cm x 50 cm bed of dry sand about 10 cm in thickness. Make sure that its top surface is levelled. Take a wooden or a plastic stool. Cut two strips of graph paper each with a width of 1 cm. Paste them vertically on any leg of the stool-one at the bottom and the other from the top. Now gently put the stool on the sand bed with its legs resting on the and Increase the size of sand bed if required. Now put a load, say a school bag full of books, on the seat of the stool. Mark the level of sand on the graph strip. This would give you the depth, if any, to which the legs of stool sink in sand. Next, turn the stool upside down so that now it rests on its seat on the sand bed. Note the depth to which the stool sinks now. Next, put the same load on the stool and note the depth to which it sinks in the sand. Compare the pressure exerted by the stool in the two situations.
Answer:
For self attempt.

Question 2.
Take a tumbler and fill it with water. Cover the mouth of the tumbler with a thick card similar to that of a postcard Hold the tumbler with one hand while keeping the card pressed to its mouth with your other hand. Turn the tumbler upside down while keeping the card pressed to its mouth. Make sure that the tumbler is held vertical.

Gently remove the hand pressing the card. What do you observe? Does the card get detached allowing the water to spill? With a little practice you will find that the card continues to hold water in the tumbler even after it is not supported by your hand. Also try this activity by using a piece of cloth to hold the tumbler in an upside down position.
Answer:
For self attempt.

Question 3.
Take 4-5 plastic bottles of different shapes and sizes. Join them together with small pieces of glass or rubber tube as shown in Fig. Keep this arrangement on a level surface. Now pour water in any one of the bottles.

Note whether the bottle in which water is poured gets filled first or all the bottle in which water is poured gets filled first or all the bottles get filled up simultaneously. Note the level of water in all the bottles from time to time. Try to explain your observations.
For more information on force and pressure visit:
→ www.glenbrook.kl2 .il.us/gbssci/phys/class/ newtlauws/u212a,html
→ www.hatesville.kl2.in.us/physics/phyNet/ Mechanics/Newton2/Pressure .html
→ www.kids.earth.nasa.gov/archive/ air_pressure/
Answer:
For self attempt.

Activities

Activity No. 11.1

Activity No. 11.5
Studying the Effect of Force on Objects

Very Short Answer Type Questions

Question 1.
Define force.
Answer:
Any push or pull is called force.

Question 2.
When does a body move?
Answer:
A body moves when force is applied.

Question 3.
What is the first requirement to put force into play?
Answer:
Interaction between two objects.

Question 4.
Give any example of push.
Answer:
Pushing a table to wall.

Question 5.
Give an example of pull.
Answer:
Pulling the door to shut.

Question 6.
When force is applied on the object in the same direction of motion, what happens?
Answer:
The speed will increase.

Question 7.
What will happen when force is applied in the direction opposite to the movement of object?
Answer:
The speed will decrease.

Question 8.
How is the strength of a force expressed?
Answer:
In magnitude.

Question 9.
What effect does force put of state of motion?
Answer:
The speed of the object may change.

Question 10.
What is the state of motion of an object?
Answer:
The speed and direction of an object is called state of motion.

Question 11.
Does the force change the direction of the moving object?
Answer:
Yes.

Question 12.
Does the force change the shape of the object?
Answer:
Yes.

Question 13.
What is the contact force?
Answer:
Force which comes in action when objects are in contact.

Question 14.
What is the muscular force?
Answer:
Force resulting due to action of muscles.

Question 15.
Give examples of muscular force.
Answer:
Bending, moving, kicking etc.

Question 16.
What kind of force is the muscular force?
Answer:
Contact force.

Question 17.
What is friction?
Answer:
Force acting equal and opposite to the moving object is friction.

Question 18.
What kind oi force is the friction?
Answer:
Contact force.

Question 19.
Give example of friction force.
Answer:
Stopping of a rolling ball.

Question 20.
Which force stops the moving striker on a carrom board?
Answer:
Friction.

Question 21.
Why does the soal of our shoes get torn away by walking?
Answer:
Due to friction between soal and road.

Question 22.
What are non-contact forces?
Answer:
Forces acting jrom distance without forming contact.

Question 23.
What is magnetic force?
Answer:
Force exerted by a magnet is called magnetic force.

Question 24.
What happens when similar poles of magnets come in contact?
Answer:
They repel each other.

Question 25.
What happens when opposite poles of magnets come in contact?
Answer:
They attract each other.

Question 26.
What is the electrostatic force?
Answer:
Force exerted by the charged bodies is called electrostatic force.

Question 27.
When a comb rubbed against hair is brought near the small pieces of paper, the paper attaches to the comb which force has attracted papers?
Answer:
Electrostatic force.

Question 28.
What kind of forces are magnetic force and electrostatic force?
Answer:
Non-contact forces.

Short Answer Type Questions

Question 1.
How do we feel force in our daily life?
Answer:
Many big or small actions make us feel the force. We have to push or pull many objects daily. A moving ball stops on its own, the ball changes the direction of its motion, when hits with a bat. We churn curd to make lassi and many other actions.

Question 2.
What is force? Define with example.
Answer:
Force is the pull or push of the objects. Actions like pushing, pulling, bending, running, lifting etc. are the examples of force. Moving or stopping or changing shape and direction of motion of objects are the various actions showing force in play.

Question 3.
What happens when two people push an object from same direction?
Answer:
When two people push or pull something together in same direction, the force applied by them get added and the action becomes easy.

Question 4.
How can force change the state of motion?
Answer:
Force can change the state of motion by changing the direction of the motion and by changing the speed of the motion. Force in the direction of the motion increases the speed and force in opposite direction decreases the speed.

Question 5.
What is the state of motion?
Answer:
State of motion of an object is its speed and its direction. State erf zero motion means state of rest. An object can be in two positions one at rest or at motion. Any change in this position can be the change in the state of motion.

Question 6.
What is muscular force? Why is it a contact force?
Answer:
The force exerted by the action of the muscles is called muscular force. Muscular activities like running, bending, walking etc. produce muscular force. Muscular force is a contact force because it is applied only when it is in contact with an object.

Question 7.
What is force of Motion? How does it arise?
Answer:
Force of friction is force opposite and equal to the force of moving body. Force of friction arises when there is a contact between two surfaces and some movement takes place in them. Force of friction is a contact force as it only arises when two surfaces come in contact with each other.

Question 8.
Why does a moving ball gradually come to rest?
Answer:
A moving bail comes to rest on its own due to force of friction. When ball moves on the ground, their surfaces come in contact to each other. The ball and the ground exert equal and opposite force on each other, which gradually brings the moving ball to a stop.

Question 9.
What is electrostatic force? What kind of a force is it?
Answer:
Electrostatic force is exerted by a charged body on another charged or uncharged body. For this it is not necessary for the two bodies to be in contact with each other. This force is applicable from a distance so it is a non-contact force.

Question 10.
What is pressure? What is the relation of pressure with area on which it is applied?
Answer:
Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we conclude that pressure increases with decrease in area.

Long Answer Type Questions

Question 1.
How will you prove that pressure of liquids decrease with increase in height ^ of its column?
Answer:
For this to be proven take aplastic

container. Take a pin and make holes in the container in horizontal line from bottom to middle of the container. Now put water in the container and observe, you will see the water will come out with maximum pressure while the hole at the top will have the minimum pressure of water.

Question 2.
What changes are caused dud to application of farce on object?
Answer:
Force when applied on an object cause many changes on the object. Following changes occur due to application of force:
(i) Force change the state of motion : Force can change the state of motion of the object. It can increase or decrease the speed of the moving object. It can change the direction of the moving object.

(ii) Force can change the shape of the object: Force can change the shape of the object on which it is applied. When force is applied on some object, it always have some effect on the shape of the object. The change in the object is some time visible and some time, it is pot visible, but change in shape of the object is always accompanied by application of force.

Question 3.
What are the contact forces? Explain different forces which are contact forces.
Answer:
Contact forces are the forces which come in play when two objects come in contact with each other. Following forces are the contact forces :
(i) Muscular Force : The force which is exerted due to action of muscles is called muscular force. Actions like bending, running, moving etc. are examples of muscular forces. It is a contact force because it comes in play when it comes in contact of the object.

(ii) Friction: Equal and opposite force being exerted on an object when its surface comes in contact with other surface. It is also a contact force because it is exerted when two surfaces come in contact with each other Halting of a moving ball on its own is an example of force of friction.

Question 4.
What are the non-contact forces? Explain different non-contact forces.
Answer:
Non-contact forces are those forces, which can be exerted from a distance without establishing a contact. Following forces are the non-contact forces :
(i) Magnetic force : Force exerted by a magnet on another magnet or magnetic substance like iron is called magnetic force. Like poles of a magnet repel each other and opposite poles of a magnet attract each other.

(ii) Electrostatic Force: Force exerted by a charged body on other charged body or uncharged body is called electrostatic force. If we rub a comb with our hair and bring it near some small bits of paper, it will attract the bits of paper towards itself. This is electrostatic force which acts without making a direct contact with other charged or uncharged object.

(iii) Force of Gravity : Earth pulls every freely falling object towards its centre. This force exerted by earth is called force of gravity. This is also a non-contact force as it acts from a distance.

Force and Pressure Class 8 HBSE Notes

• Every push or pull is called force.
• Force comes into action when an object interacts with other object.
• Forces when implied in same direction add to each other, but when applied in opposite directions, they cancel each other. Equal forces applied in opposite direction results in net zero force.
• Force has magnitude and direction.
• Force can bring many changes in body on which it is applied.
• Force can change the speed of the moving body. Force in same direction of motion can increase the speed and in opposite direction can decrease the speed.
• Force can change the direction of the object in motion or at rest.
• Force can change theshapeof theobject. Force when applied on an object is always accompanied by change’in its shape.
• Two objects when come in contact with each other, they apply force on each other, this is called contact force. Muscular force, friction force etc. are examples of contact force.
• Force acting opposite to the direction of motion of a moving object is called force of friction.
• Force which acts from a distance is called a non-contact force.Magnetic force, electrostatic force and gravitational force are the examples of non-contact force.
• Force exerted per unit area is called pressure.
• Liquids and gases also exert pressure in all directions.
• Pressure exerted by air is called atmospheric pressure.

Haryana Board HBSE 8th Class English Solutions Honeydew & It So Happened

HBSE 8th Class English Solutions Honeydew

HBSE Haryana Board 8th Class English Honeydew Prose

• Chapter 1 The Best Christmas Present in the World
• Chapter 2 The Tsunami
• Chapter 3 Glimpses of the Past
• Chapter 4 Bepin Choudhury’s Lapse of Memory
• Chapter 5 The Summit Within
• Chapter 6 This is Jody’s Fawn
• Chapter 7 A Visit to Cambridge
• Chapter 8 A Short Monsoon Diary
• Chapter 9 The Great Stone Face 1
• Chapter 10 The Great Stone Face 2

HBSE Haryana Board 8th Class English Honeydew Poem

• Poem 1 The Ant and the Cricket
• Poem 2 Geography Lesson
• Poem 3 Macavity: The Mystery Cat
• Poem 4 The Last Bargain
• Poem 5 The School Boy
• Poem 6 The Duck and the Kangaroo
• Poem 7 When I Set Out for Lyonnesse
• Poem 8 On the Grasshopper and Cricket

HBSE 8th Class English Solutions It So Happened

HBSE Haryana Board 8th Class English Supplementary Reader It So Happened

• Chapter 1 How the Camel Got His Hump
• Chapter 2 Children at Work
• Chapter 3 The Selfish Giant
• Chapter 4 The Treasure Within
• Chapter 5 Princess September
• Chapter 6 The Fight
• Chapter 7 The Open Window
• Chapter 8 Jalebis
• Chapter 9 The Comet 1
• Chapter 10 The Comet 2

Haryana State Board HBSE 8th Class Science Solutions Chapter 16 Light Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 16 Light

HBSE 8th Class Science Light Textbook Questions and Answers

Question 1.
Suppose you are in a dark room. Can you see object in the room? Can you see objects outside the room. Explain.
Answer:
We cannot see objects in the room because it is a dark room. No light is reflected from the surfaces of the object, so we are not able to see them. But outside the room, the objects can reflect light thus enabling us to see the objects.

Question 2.
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer:
Following are the differences between a regular reflection and diffused reflection :
Regular Reflection:
(i) It takes place on a smooth surface.
(ii) It has all the reflected rays in parallel.
(iii) Reflected rays are in one direction.

Diffused Reflection:
(i) It takes place on a rough surface.
(ii) Reflected rays are not parallel.
(iii) Reflected rays are scattered in different directions.
Diffused reflection is not due to failure of laws of reflection.

Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble stone with water spread over it
(e) Mirror
(f) Piece of paper
Answer:
(a) A polished wooden table will have regular reflection because its surface is smooth.
(b) A chalk powder will ‘get the diffused reflection because chalk particles are not smooth.
(c) Cardbord surface has minute irregularities on it, so it will have a diffused reflection.
(d) Marble stone with water spread over it will have regular reflection if water is stable but if waves are formed then diffused reflection will take place.
(e) A mirror will reflect light regularly due to its smooth surface.
(f) A piece of paper will have irregular reflection due to minute irregularities on it.

Question 4.
State the laws of reflection.
Answer:
Following are the laws of reflection:
(i) Incident ray, reflected ray and normal drawn at the point of incidence to the reflecting surface always lie in the same plane.
(ii) Angle of incidence is always equal to angle of reflection.

Question 5.
Describe an activity to show that the incident rays, the reflected ray and the normal at the point of incidence lie in the same plane.
Answer:
Take a plane mirror and make it stand with help of block on a plane sheet as shown in figure. Now draw an incident line on it AB. Now see in the mirror and mark the points on the paper, where you feel the line is travelling after

getting reflected from the mirror (P₁ and P₂). Now remove the mirror and mark it as OS and Join the points to make the reflected ray. You will see that, it joins the point of incidence, proving that incident ray is the reflected ray (BC).

Question 6.
Fill in the blanks in the following:
(a) A person 1 m in front of a plane mirror seems to _________ be m away from his image.
(b) If you touch your _________ ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with .
(c) The size of the pupil becomes _________ when you see in dim light.
(d) Night birds have _________ cones than rods in their eyes.
Answer:
(a) 2 m
(b) left, left
(c) increase
(d) lesser.

Choose the correct option in the Question 7-8.

Question 7.
Angle of incidence is equal to the angle of reflection:
(i) Always
(ii) Sometimes
(iii) Under special conditions
(iv) Never
Answer:
(i) Always.

Question 8.
Image formed by a plane mirror is:
(a) virtual, behind the mirror and enlarged
(b) virtual, behind the mirror and of the same size as the object
(c) teal at the surface of the mirror and enlarged
(d) real, behind the mirror and of the same size as the object.
Answer:
(b) virtual, behind the mirror and of the same size as the object.

Question 9.
Describe the construction of kaleidoscope.
Answer:
Kaleidoscope is made of three strips of plane mirrors. Three strips of plane mirrors of about 15 cm. length and 4 cm. width are taken and arranged as in a prism i.e. in a triangular form.

They are fixed to each other with thick sheet of paper and enclosed in a tube or in a circular carboard. One end of the tube is covered with a round cardboard disc having a hole in the centre. From the opposite open end some pieces of broken bangles or broken coloured glass are put inside the tube. This open end is also closed. When we see inside this tube through the hole in the circular cardboard; we see different patterns of coloured bangle inside it.

Question 10.
Draw a labeled sketch of human eye.
Answer:

Question 11.
Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise ?
Answer:
Teacher has advised her to because laser light is harmful for eyes and can cause some permanent damage to eyes when throw directly in eyes.

Question 12.
Explain how you can take care of your eyes?
Answer:
Following precautionary measures can be taken to take care of our eyes:

• We should always wash our eyes with plane cold water atleast three times a day.
• We should not touch our eyes with dirty hands.
• We should never rub our eyes.
• We should not look at Sun directly.
• We should read book, watch T.V., read from black board from a suitable distance.
• Consult an eye specialist if have any irritation, redness in our eyes.

Question 13.
What is the angle of incidence of a ray if the incident and reflected rays is at an angle of 90° to the incident ray?
Answer:
The angle of incidence of the ray will be 45°.

Question 14.
How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Answer:
Infinite images will be formed.

Question 15.
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the figure. Draw the reflected ray from the second mirror.

Answer:

Question 16.
Bhoojo stands at A just on the side of a plane mirror as shown in figure. Can he see himself in the mirror ? Also can he see image of objects situated at P, Q and R?

Answer:
Bhoojo can’t see himself. He can see the images of objects at P and Q.

Question 17.
(a) Find out the position of the image of an object situated at A in the plane mirror, (figure)
(b) Can Paheii at B see this image?
(c) Can Bhoojho at C see this image?
(d) When Paheii moves from B to C, where does the image of A move?

Answer:
(a) Image will be formed at ‘A’.
(b) Yes, Paheii at B can see the image.
(c) No, Boojho can’t see the image at C.
(d) The image will disappear at Paheii moves from B to C.

Extended Learning – Activities and Projects

Question 1.
Make your own mirror. Take a glass strip or glass slab. Clean it and put it on a white sheet of paper. See yourself in the glass. Next put the glass slab on a black sheet of paper. Again look into the glass. In which case do you see yourself better and why?
Answer:
For self attempt.

Question 2.
Make friends with some visually challenged students. Enquire from them how they read and write. Also find out how they are able to recognise objects, hurdles and currency notes.
Answer:
For self attempt.

Question 3.
Meet an eye specialist. Get your eye sight checked and discuss how to take care of your eyes.
Answer:
For self attempt.

Question 4.
Survery your neighbourhood. Find out how many children below the age of 12 years use spectacles. Find out from their parents what, in their view, could be the reason for the weak eyesight of’ their children.
You can read more on this topic on the following websites :
→ www.glenbrook.k 1 2.il.us/gbssci/phys/ mmedia/optics/ifpm.html
→ www.glenbrook.k 1 2 il.us/gbssci/phys/elass/ refln/u131b.html
Answer:
For self attempt.

HBSE 7th Class Science Light Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is sense of sight?
Answer:
The sense which enables us to see object around us is called sense of sight.

Question 2.
What are the sight organs in animals?
Answer:
Eyes.

Question 3.
What is a mirror?
Answer:
Smooth and shiny surface is called a mirror.

Question 4.
What is reflection?
Answer:
Throwing back the incident light by a plane surface is called reflection.

Question 5.
What kind of surfaces reflect light?
Answer:
All surfaces reflect light.

Question 6.
What is incident ray?
Answer:
Beam of light falling on reflecting surface is called incident ray.

Question 7.
What is reflecting ray?
Answer:
Beam of light reflected back by the reflecting surface is called reflected ray.

Question 8.
What is angle of incidence?
Answer:
Angle formed between the incident ray and normal is called angle of incident.

Question 9.
What is angle of reflection?
Answer:
Angle formed between the reflecting ray and normal is called angle of reflection.

Question 19.
State second law of reflection.
Answer:
Angle of incidence and angle of reflection are always same.

Question 11.
What kind of image is formed by a plane mirror?
Answer:
Virtual and erect image.

Question 12.
Where is the image formed by the mirror?
Answer:
Behind the mirror.

Question 13.
What is the size of the image formed?
Answer:
Same as that on the object infront of the mirror.

Question 14.
At what distance is the image formed behind the plane mirror?
Answer:
At the same distance, as is the object infront of the mirror.

Question 15.
What is the phenomenon called where left side appears to be right and vice- versa in a plane mirror?
Answer:
Lateral inversion.

Question 16.
Which surface shows regular reflection?
Answer:
Smooth surface.

Question 17.
Which surface shews diffused reflection?
Answer:
Rough surface.

Question 18.
What kind of reflection will take place from a polished leather shoes top?
Answer:
Regular reflection.

Question 19.
What kind of reflection will take place from the cover of your note-hook?
Answer:
Diffused reflection.

Question 20.
In what kind of reflection does reflected rays go parallelled to each other?
Answer:
Regular reflection.

Question 21.
In what kind of reflection, reflected rays move scattered?
Answer:
In diffused reflection.

Question 22.
floes Moon has its own light?
Answer:
No.

Question 23.
How does moon shine?
Answer:
It reflected light emitted by the Sun.

Question 24.
Name some objects which have light of their own.
Answer:
Sun, fire, flame of candle etc.

Question 25.
What are objects called, which have light of their own?
Answer:
Luminous objects.

Question 26.
How many mirror strips are used to make a Kaleidoscope?
Answer:
Three.

Question 27.
Is white light a pure white light?
Answer:
No.

Question 28.
How many colours constitute a white beam?
Answer:
Seven.

Question 29.
What is the splitting of white light into its constituent colours called?
Answer:
Dispersion.

Question 30.
What is the shape of human eye?
Answer:
It is roughly spherical in shape.

Short Answer Type Questions

Question 1.
What is reflection of light?
Answer:
When a beam of light falls on a surface, it is thrown back by the surface in a different direction in the same medium. This is called reflection of light. Every surface can reflect. The falling beam of light is called incident ray and beam bouncing back is called the reflected ray.

Question 2.
How do we see various objects?
Answer:
We see various objects due to reflection. As we know all surfaces reflect light, when light falls on any object, it reflects the light. The reflected light reaches our eyes and we are enabled to see the objects.

Question 3.
Write the laws of reflection?
Answer:
There are two laws of reflection :
(i) The ray of incidence, ray of reflection and normal drawn at the point of incidence to the reflecting surface lie in the same plane.

(ii) The angle of reflection and angle of incidence are always equal.

Question 4.
What do you mean by following.
(i) Incident ray
(ii) Reflected ray
Answer:
Incident ray : The light ray that strikes any surface is called incident ray.
Reflected ray : The light ray which is thrown away from the surface after reflection in a different direction, is called reflected ray.

Question 5.
What do you mean by angle of incidence and angle of reflection?
Answer:
The angle formed between the incident ray and the normal is called the angle of incidence. The angle of reflection is the angle formed between the reflected ray and the normal. Both these angles are always equal in size.

Question 6.
What is a mirror? What kind of image is formed in a mirror?
Answer:
Any smooth and shining surface can act as mirror. Mirror is a smooth surface which is polished from its back and can form the image of the object which is placed in front of it. The image formed by a mirror is a virtual and erect image and is of same size as that of the object infront of it.

Question 7.
What is dispersion of light?
Answer:
A beam of white light consists of seven colours. When a beam of white light passes through a prism, it splits into its seven constituent colours. The splitting of white light into its seven constituent colours is called dispersion of light.

Question 8.
How many kind of nerve endings are there in our eyes?
Answer:
There are two types of nerve endings in our eyes. The first type of nerve endings are called cones. Cones are sensitive to bright light and other type of nerve endings are called rods. Rods are sensitive to dim light cones are also sensitive to colours.

Question 9.
How do eye muscle adjust themselves to see the near and distant objects?
Or
What is called the accomodation of eyes?
Answer:
The muscles of the eye contract in order to see near objects. When they contract the lens becomes thicker. When the eye has to see a distant object the muscles expand or relax. This makes the lens thinner. This is called accommodation.

Question 10.
What is the cause of dispersion?
Answer:
Different colours of light bend by different angles of refraction. When light enters the glass prism or a drop of water, different colours bend at different angles and become separated to show phenomenon of dispersion.

Question 11.
How do ciliary muscles affect the functioning of eye?
Answer:
Ciliary muscles can contract and relax. Because of this they can change the thickness of eye lens which also changes its focal length. With change in focal length eye lens can make image of near by objects and also far away objects. So power of accommodation of eye is due to the function of the ciliary muscle.

Question 12.
What is a yellow spot in eyes?
Answer:
Yellow spot or macula is a small area, facing the eye lens. It has high concentration of light sensitive nerve endings or cones. The rest of the retina has lesser cones and more number of cells called rods. It is the spot where brightest vision is formed and colour version is formed.

Question 13.
What is the blind spot?
Answer:
It is a region below the yellow spot, where no light sensitive nerve endings are present. It is an area of no vision.

Question 14.
What is Myopia or short sightedness?
Answer:
This is a type of eye defect, in which person can see nearer objects clearly but cannot see the far off objects. This defect is due to thickness of eye lens. Ciliary muscles do not relax enough to make lens thin enough to see distant objects.

Question 15.
What is Hypermetropia or long sightedness?
Answer:
This is a type of an eye defect, in which the person can see far off objects clearly, but cannot see the nearer objects. This defect is due to thinness of the eye lens. The ciliary muscle do not contract enough to make the lens see nearer objects.

Question 16.
What is cataract? How can it be corrected?
Answer:
During old age, the eye sight becomes blurred. It happens because the lens of the eye becomes opaque and milky. When the vision becomes cloudy the person is said to have cataract. It is possible to treat this temporary loss of vision by removing the opaque lens and, a new artificial lens is inserted by minor and simpe operation.

Question 17.
Write any three safety measures to protect our eyes.
Answer:

• We should not rub our eyes.
• We should wash our eyes many times a day.
• We should not look at sun or other powerful lights directly.

Question 18.
What is Braille system?
Answer:
Braille is based on code of one to six dots which are raised. Each dot has a position. These dots make up letters of alphabet, number and all other things done in print. Any language can be read through the codes of the braille by touching the dots.

Long Answer Type Questions

Question 1.
What is reflection of light? State laws of reflection.
Answer:
Reflection of light is throwing back of light by any object. When a beam of light falls on some surface, the surface throws that beam away in different direction. This is called reflection of light. Following are the laws of reflection:

(a) When a ray of light falls on a reflecting surface, it is reflected in such a way that the angle of incidence is equal to the angle of reflection i.e. ∠i = ∠r.

(b) The incident ray, the normal and the reflected ray, all lie in the same plane.

Question 2.
What are the characteristics of image formed with a plane mirror?
Answer:
Plane mirror is a shiny, polished surface. When any object is placed in front of the mirror, an image is formed. Following are the characteristics of the image formed by a plane mirror:

• Image formed on a plane mirror cannot be taken on a screen, such image is called a virtual image.
• Image formed on a plane mirror is erect.
• It is laterally inverted i.e. left hand of the object appears as the right hand.
• Image formed is as far behind as the object is in front of it.

Question 3.
What are the uses of a plane mirror?
Answer:

• We use a plane mirror to see our reflections in it, at our homes.
• Plane mirrors are used to reflect light on a particular object.
• Plane mirrors are used for signalling by scouts and army.
• They are used to form multiple images in show windows.
• Plane mirror is used to reflect sun rays in appliances like solar cooker etc.
• Toys like Kaleidoscope are made on the concept of multiple reflection. Navy use periscopes based on concept of multiple reflection for spying in sea.

Question 4.
Describe how does human eye work?
Answer:
The light reflected by objects enter our eyes through cornea. That is why cornea is called window to the world. Lens focuses the image of the object on the retina. Retina converts these optical images into optical pulses. These optical pulses are then sent to brain through optical nerves. The amount of light entering the eye through cornea is controlled by Iris. It expands when light is bright and thus enables the pupil to enter controlled amount of light to enter the eye. In dark it contracts and increases the size of pupil to allow more light to enter the eye.

The retina forms a small and inverted image of the object. The brain interprets it and forms the erect and correct sized image.

Question 5.
Write various measures to save our eyes.
Answer:
Eyes are a precious gift of God. We should take proper care of our eyes and protect them from injury. Following measures should be taken for healthy eyes :

• We should wash our eyes with cold water everyday and wipe them with clean and soft cloth.
• We should never rub our eyes. If some particle enters our eyes, we should wash our eyes with cold water.
• We should always read in proper light.
• In case of any injury or other problems related to eyes, we should avoid self medication and immediately consult an eye specialist.

Question 6.
What is blindness? How many types of blindness do we know about?
Answer:
A person is said to be blind or visually impaired when he or she is imable to see. Blindness is of two types:
Curable Blindness : When cornea becomes opaque or the lens becomes opaque the sight of the person becomes decreased. This is called a temporary or curable blindness. In this case the person is operated upon and sight is resorted. An artificial lens is inserted in place of opaque lens and the opaque cornea is replaced with a healthy donated cornea.

Permanent Blindness : In this type of blindness image formed by cornea is not transferred to brain and this type of blindness cannot be cured.

Pollution of Air and Water Class 8 HBSE Notes

• We see all the things around us only due to sense of sight.
• Eyes are our organs of sight, which enables us to see objects around us.
• It is the light which enables our eyes to see the objects. Without light our eyes cannot sense anything.
• Any polished or shiny surface acts as a mirror. It can change the direction of light.
• Light is reflected from all the surfaces.
• When a beam of light falls on a surface, it throws back the light to same medium. This phenomenon is called reflection of light.
• The beam of light falling on the plane surface is called the incident ray.
• The beam of light thrown back by the reflecting surface is called the reflected ray.
• The line drawn between the point where the incident ray and reflected ray meet is called the normal.
• The angle between the normal and the incident ray is called angle of incidence.
• The angle between the normal and the reflected ray is called the angle of reflection.
• The angle of incidence and the angle of reflection are equal.
• Incident ray, reflected ray and the normal drawn at the point of incidence to reflecting surface lie in the same plane.
• Above two points are called laws of reflection.
• Light falling on a smooth surface is reflected regularly.
• Irregular or diffused reflection takes place on rough surface.
• In mirror the right appears as left and left as right. This is called lateral inversion.
• Two mirrors inclined to each other at different angles, give multiple images.
• White light consists of seven colours called spectrum.
• Splitting of white light into its constituting seven colours is callled dispersion.
• Our eyes have different parts which perform different functions to enable us to see the objects.
• Visually challanged persons can read and write using Braille system.

Haryana State Board HBSE 8th Class Science Solutions Chapter 4 Materials: Metals and Non-Metals Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 4 Materials: Metals and Non-Metals

HBSE 8th Class Science Materials: Metals and Non-Metals Textbook Questions and Answers

Question 1.
Which of the following can be beaten into thin sheets?
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc.

Question 2.
Which of the following statements is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
Answer:
(a) All metals are ductile. ✗
(b) All non-metals are ductile. ✗
(c) Generally, metals are ductile. ✓
(d) Some non-metals are ductile. ✗.

Question 3.
Fill in the blanks:
(a) Phosphorus is very ……….. non-metal.
(b) Metals are ……….. conductor of heat and ………….. .
(c) Iron is ………….. reactive than copper.
(d) Metals react with acids to produce ………….. gas.
Answer:
(a) reactive
(b) good, electricity
(c) less
(d) hydrogen.

Question 4.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Generally, non-metals react with acids. ( )
(b) Sodium is a very reactive metal. ( )
(c) Copper displaces zinc from zinc sulphate solution. ( )
(d) Carbon can be drawn into wires. ( )
Answer:
(a) False
(b) True
(c) False
(d) False.

Question 5.
Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of their properties.

Answer:

Question 6.
Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Answer:
(a) Aluminium foils are used to wrap food items because aluminium can be beaten in sheets to form these thin wrapping sheets and it is soft and it does not react with food items.

(b) Immersion rods are made up of metallic substances because metals are good conductors of heat and electricity. They get hot very soon on passage of current and warm the water.

(c) Copper cannot displace zinc from its salt solution because copper is less reactive than zinc. A less reactive metal cannot displace a more reactive metal from its solution.

(d) Sodium and Potassium are stored in kerosene because they are very reactive and quickly react in air.

Question 7.
Can you store acidic lemon pickles in an aluminium utensils? Explain.
Answer:
No, we cannot store acidic lemon pickles in aluminium utensils because aluminium is a metal. Metals readily react with acids to produce hydrogen gas. So, when the aluminium metal comes in contact with acidic lemon pickles, it would react to release hydrogen, which would spoil the food and render it unfit to consume.

Question 8.
In the following table some substances are given in Column I. In Column II some uses are given. Match the items in Column I with those in Column II.

Answer:

Question 9.
What happens when:
(i) Dilute sulphuric acid is poured on a copper plate?
(ii) Iron nails are placed in copper sulphate solution?
Write word equations of the reactions involved.
Answer:
(i) When sulphuric acid is poured on copper plate the acid present in sulphuric acid reacts with copper to form copper sulphate and hydrogen. The copper plate gets eroded from place.
Sulphuric Acid + Copper → Copper Sulphate + Hydrogen
(ii) When iron nails are placed in copper sulphate solution the iron being more reactive will replace copper in its salt solution,
(Ferrous Sulphate) → Iron + Copper Sulphate → Iron Sulphate + Copper
The solution will turn light green.

Question 10.
Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.
(i) How will she find the nature of the gas?
(ii) Write down equations of all the reactions taking place in this process.
Answer:
(i) She will test it with litmus paper to check the acidic or basic nature of gas. If red litmus turns blue, it is basic in nature. If blue litmus turns red, it is acidic in nature.

(ii) Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₃).

Question 11.
One day Reeta went to a Jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back they found that there was a loss in its weight. Can you suggest a reason for the loss in weight?
Answer:
When gold is washed in acidic solution, it being a metal reacts with acid and forms the hydrogen gas with some metallic oxides. This causes the loss of gold in form of gold oxides. This looses the weight of gold.

Activity.

No. 4.1. Malleability Of Materials

No. 4.3. Electrical Conductivity Of Materials

Extended Learning – Activities And Projects

Question 1.
Prepare Index Cards for any four metals and non-metals. The card should have information like name of metal/non-metal; its physical properties, chemical properties and uses.
Answer:
1. Name of metal: Copper
Physical properties:
(i) It is hard
(ii) It is ductile.
(iii) It is good conductor of heat and electricity.

Chemical Properties:
(i) Copper reacts with moist air to form greenish coating.
(ii) It oxide is basic in nature.
(iii) It reacts with acids to produce hydrogen gas.
(iv) It displaces iron from iron sulphate solution.

Uses:
Copper is used to make electrical wires, base of cooking utensils, etc.

Non-metals:

2. Name of non-metal: Coal
Physical properties:
(i) It is not ductile.
(ii) It is not malleable.
(iii) It is hot sonorous and does not shine. It is soft.
(iv) It is poor conductor of electricity

Chemical Properties:
(i) It produces oxides of carbon when burnt
(ii) It’s oxide are acidic in nature.
(iii) It does not take part in replacement reaction.

3. Name of Non-metal: Sulphur
Physical properties:
(i) It is neithre ductile nor malleable.
(ii) It is soft and dull.
(iii) It is poor conductor of heat and electricity.

Chemical properties:
(i) It reacts with oxygen to produce sulphur dioxide.
(ii) It reacts with water to form sulphurous acid H₂SO₄ which is acidic in nature.
(iii) Metals are heated to mould them.
(iv) Gold is preferred to prepare jewellary because it is less reactive ductile and is a costly metal.

4. Name of Metal: Iron
Physical properites:
1. malleable
2. non-ductile
3. sonorous
4. hard
5. good conductor of heat and current.

Chemical properties:
1. React with oxygen to form rust.
2. React with water.
3. React with acids to form hydrogen gasi
4. React with sodium hydroxide to produce hydrogen gas.

Uses:
Used to make machines, tools, door, etc.

Question 2.
Visit a blacksmith and observe how metals are moulded.
Answer:
For self attempt.

Question 3.
Suggest an experiment to compare the conductivity of electricity by iron, copper, aluminium and zinc. Perform the experiment and prepare a short report on the results.
Answer:
For self attempt.

Question 4.
Find out the locations of the deposits of iron, aluminium and zinc in India. Mark these in an outline map of India. In which form are the deposits found? Discuss in the class.
Answer:
For self attempt.

Question 5.
Discuss with your parents / neighbours / goldsmiths why gold is preferred for making jewellery.
Answer:
For self attempt.

Question 6.
Visit the following websites and enjoy the quiz on metals and non-metals.

• chemistry.about.com /library/weekly/ bl05030a.htm
• chemistry.about.com / od / testsquizzes / Chemistry_Tests_Quizzes.htm.
• www.syvum.com / cgi / online / mult.cgi / squizzes / science / metals.tdf?0
• www.gcsescience.com / q / quesemet.html
• www.corrosionsource.com / handbook / periodic / metals.htm
  Answer:
  For self attempt.

HBSE 8th Class Science Materials: Metals and Non-Metals Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is meant by malleability of a metal?
Answer:
The property by virtue of which a metal can be hammered into thin sheets is called malleability.

Question 2.
What is meant by ductility of metals?
Answer:
Ductility of metals means that they can be drawn into very thin wires.

Question 3.
Name two metals which are both malleable and ductile.
Answer:
Gold and silver.

Question 4.
Are non-metals malleable and ductile?
Answer:
No.

Question 5.
Name a metal which exists in liquid state.
Answer:
Mercury.

Question 6.
Name the hardest substance in the world.
Answer:
Diamond.

Question 7.
Which metal is the best conductor of electricity?
Answer:
Silver.

Question 8.
Identify the most reactive and the least reactive metal amongst the following:
Al, K, Cu, Au.
Answer:
K is the most reactive while Au is the least reactive metal.

Question 9.
Name the metal which is stored in kerosene oil.

Answer:
Sodium is stored in kerosene oil.

Question 10.
Which metal foil is used in packing of some medicine tablets?
Answer:
Aluminium.

Question 11.
Which metal foil is used for decorating sweets?
Answer:
Silver.

Question 12.
Name a non-metal which is good conductor of heat.
Answer:
Graphite.

Question 13.
Why do gold and silver exist in free state?
Answer:
Gold and silver exist in free state because they are less reactive.

Question 14.
What would happen to the iron railings in open, when not painted?
Answer:
They will be rusted.

Question 15.
Why electric wires are made of copper?
Answer:
Electric wires are made of copper because it is good conductor of electricity.

Question 16.
Iron nails are kept dipped in blue copper sulphate solution and solution gets changed into light green colour. Why?
Answer:
This happens because iron displaces copper to form Ferrous Sulphate which is light green in colour.

Question 17.
Explain why silver does not displace hydrogen from dil HCl?
Answer:
Silver is less reactive than hydrogen, so it does not displace hydrogen from dil HCl.

Question 18.
When does red litmus paper turn blue?
Answer:
When red litmus paper comes in contact with basic solution.

Question 19.
When does a blue litmus paper turn red?
Answer:
Blue litmus paper turns red when it comes in contact with acidic solution.

Question 20.
What happens when sulphur dioxide gets dissolved in water?
Answer:
Sulphurous acid is formed:
SO₂ + H₂O → H₂SO₃

Question 21.
Oxides of non-metals are generally of which nature?
Answer:
Oxides of non-metals are generally of acidic nature.

Question 22.
What happens when sodium comes in contact with water?
Answer:
Sodium catches fire and heat is released.

Question 23.
How do non-metals react with water?
Answer:
Non-metals do not react with water.

Question 24.
How do non-metals generally react with acids?
Answer:
Non-metals generally do not react with acids.

Question 25.
Which gas is emitted when metals react with acids?
Answer:
Hydrogen gas.

Question 26.
Write any use of non-metal.
Answer:
Non-metals are used in crackers.

Question 27.
Write any use of metals.
Answer:
Metals are used to make all means of transportation.

Question 28.
What is a displacement reaction?
Answer:
Reaction in which a more reactive metal displaces the less reactive metal from its compound in aqueous solution is called displacement reaction.

Short Answer Type Questions

Question 1.
Write any three physical characteristics of metals.
Answer:
(i) Metals can be hammered to make sheets so they are malleable.
(ii) Metals can be drawned into very thin wires, that means metals are ductile.
(ii) Metals are good conductors of heat and electricity.

Question 2.
Write any three physical characteristics of non-metals.
Answer:
(i) Non-metals are non-ductile and non- malleable.
(ii) Non-metals are non-sonorous.
(iii) Non-metals are poor conductors of heat and electricity.

Question 3.
What do you mean by sonorous materials?
Answer:
Materials which make a sound when they are hit hard with some other material are called sonorous materials. All metals except the soft ones are sonorous, while all non-metals are non-sonorous.

Question 4.
How do metals and non-metals react with oxygen?
Answer:
Metals react with oxygen to form oxides generally. These oxides are alkaline.
\(\begin{array}{ccc}
2 \mathrm{Mg} & +\mathrm{O}_{2} \rightarrow & 2 \mathrm{MgO} \\
\text { Magnesium } & \text { Oxygen } & \text { Magnesium oxide }
\end{array}\)
Non-metals also react with oxygen to form oxides but these oxides are acidic in nature.
\(\begin{array}{cc}
\mathrm{C} & \mathrm{O}_{2} \\
\text { Carbon } & \text { Oxygen }
\end{array} \quad \rightarrow \quad \mathrm{CO}_{2}\)

Question 5.
A copper coin is kept immersed in a solution of silver nitrate for some time. What will happen to the coin and the colour of the solution?
Answer:
Copper is more reactive than silver. Therefore, when a copper coin is kept immersed in a solution of silver nitrate, it will displace silver from silver nitrate solution and a solution of copper nitrate will be formed.
Thus, the copper coin will dissolve in the solution and the colour of the solution will change from colourless to blue.

Question 6.
Explain why zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution.
Answer:
Zinc metal is more reactive than copper. Therefore, it can displace copper from CuS0₄. Cu is less reactive than Zn, therefore, cannot replace Zn from ZnS0₄.

Zn + CuSO₄ → ZnSO₄ + Cu

Question 7.
State any three reasons for counting sulphur amongst the non-metals.
Answer:
Sulphur is a non-metal because:
(i) It is neither malleable nor ductile.
(ii) It does not conduct heat and electricity.
(iii) It combines with oxygen to form acidic oxide.

Question 8.
Non-metals do not react with water. How does this fact is utilized to store very reactive non-metals?
Answer:
Non-metals do not react with water. This quality is quite helpful in protecting some highly reactive non-metals which quickly react in air. Phosphorus is very reactive non-metal. It immediately catches fire when exposed to air. To prevent this, it is stored in water.

Question 9.
What is an element?
Answer:
Element is the smallest unit of any material. It cannot be broken further by cooling, heating or by electrolysis e.g. sulphur, iron, carbon etc.

Question 10.
Compare the physical properties of metals and non-metals.
Answer:

Question 11.
Compare the chemical properties of metals and non-metals.
Answer:

Question 12.
In which state do metals occur inside the earth’s crust?
Answer:
Metals occur in different states inside the earth’s crust depending upon their reactivity. Some metals occur in elemental state or in the form of compounds. Reactive metals generally are found in compound. Highly unreactive metals occur in free state while the less reactive metals can either be found in combined state or infree state.

Question 13.
What do you mean by Malleability of metals.
Answer:
The physical property of metals by virtue of which metals can be beatan into thin sheet is called malleability. Most of the metals are malleable. Aluminium is beaten into aluminium foil for wrapping food and silver is also beaten to make silver foils to decorate sweets.

Question 14.
What do you mean by ductility?
Answer:
The physical property by virtue of which metals can be drawn into thin wires is called ductility. Metals which are good conductors of electricity are mostly drawn into wire to be used in electrical cables. Gold and silver are the most ductile metal. Wires of copper, aluminium and tungsten are used to make electricity cables and tungsten is used to make filaments of bulbs. Aluminium wires are also widely used to make electrical wires.

Question 15.
What is an alloy? Describe any one alloy.
Answer:
Mixture of two or more than two metals to get desired qualities is called an alloy. Stainless steel is an alloy of iron, chromium and nickel. It is used to make utensils, surgical & instruments and many other decorative items. Stainless stell is hard and do not rust.

Long Answer Type Questions

Question 1.
Write a short note on displacement reaction of metals.
Answer:
A more reactive metal displaces a less reactive metal from its compound in an aqueous solution. This is called displacement reaction. For example, when some iron nails are dipped in copper sulphate solution, the iron being more reactive displaces copper from its solution and form ferrous sulphate solution of light green colour.

Similarly, magnesium and zinc also displaces copper from its compound.

Question 2.
How will you prove the nature of rust or the ash obtained from burning magnesium ribbon?
Answer:
This can be easily proved in laboratory. Take some rust and dissolve it in water (a few drops). Now take a red litmus paper and dip the litmus paper in solution. We will see that the red litmus paper turns blue.

When the red litmus paper turns blue it means solution is basic in nature. So the rust is basic in nature. We can similarly check the nature of ash obtained by burning a magnesium ribbon. It will also turn red litmus paper blue proving its basic nature.

Question 3.
How do different metals react with water?
Answer:
Different metals react differently with water, hydrogen being a common end product.
Sodium metal reacts vigorously with water to form sodium hydroxide and hydrogen gas.

Magnesium only reacts with hot boiling water to form magnesium oxide and hydrogen.

Red hot iron reacts with steam to form iron oxide and hydrogen copper. Silver and nickel do
not react with water.

Question 4.
What are the different uses of metals?
Answer:
Metals are very useful to us. Some of the uses of common metals are following:
(а) Copper and aluminium metals are used to make electric wires. This is because copper and aluminium are good conductors of electricity.
(b) Copper, aluminium and iron metals are used for making utensils and other domestic things. These metals are also used to make various factory equipments. This is because, all these metals are good conductors of heat.
(c) Iron is used to make heavy machinery and is also used in construction of buildings because it is very heavy and strong.
(d) Thin foils of aluminium are used in packaging food materials and medicines etc.
(e) The liquid metal mercury is used in thermometers.
(f) Gold and silver metals are used to make jewellery.
(g) Sodium, titanium and zirconium metals are used in atomic energy and space projects.

Question 5.
What are the different uses of non-metals?
Answer:
Following are the uses of non-metals:
(a) Oxygen is used by plants and animals for respiration. Oxygen also supports the process of combustion in factories, houses, aeroplanes
and missiles.
(b) Compounds of nitrogen provide nutrients to soil and plants. Fertilizers made by using nitrogen are extensively used in agricultural practices.
(c) Chlorine is used to disinfect the drinking water as it has the ability to kill germs.
(d) Sulphur is also used as germicide, it is also used as an antiseptic fcr skin treatment (in ointments).
(e) Non-metals are used in crackers.

Question 6.
What is corrosion? How does it affect different metals?
Answer:
Corrosion is defined as attack of atmospheric gases and moisture on the surfaces of metal making them deformed and weak. If iron is left in open for a period of time, it slowly gets deposits of brown flakes on it, which is called rusting of iron. It is undesirable because it makes the iron weak and eat it up slowly with passage of time. Similarly silver objects become black in colour and loose their lustree as silver reacts with hydrogen sulphide gas of air. Slowly the copper vessels also get coated with greenish layer of copper carborate. It is formed due to reaction of copper with carbondioxide of air and water vapour also present in air.

Question 7.
Write composition, properties and uses of following alloys: Steel, Stainless Steel, Brass and Duralumin
Answer:

Materials: Metals and Non-Metals Class 8 HBSE Notes

1. All metals and non-metals have some physical and chemical properties which differentiate them from each other.
2. Properties related to appearance and structure are called physical properties while how they react with other metals and non-metals are called their chemical properties.
3. Metals are shiny in appearance. This property of metals is called lustre.
4. Metals are generally hard. Sodium and potassium are soft. All metals mostly exist in solid state except murcury which is a liquid at room temperature.
5. Metals can be beaten with hamrqer and can be beaten into sheets. This physical property of metals is called malleability. Most of the metals are malleable.
6. Metals can be drawn into wires, they are thus ductile . Gold, tungsten are highly ductile metals.
7. Metals are good conductors of heat and electricity. That is why metals are used to make electric wires and most of the cooking utensils are made of metals. Silver is the best conductor of electricity.
8. Metals make sound, when they are hit hard with other object. This property makes them sonorous.
9. Non-metals do not shine and break-up when hit hard with hammer.
10. Non-metals cannot be beaten into sheets.
11. Non-metals cannot be drawn into wires.
12. They do not make any sound when hit with other objects.
13. Non-metals are bad conductors of heat and electricity.
14. Metals and non-metals react with oxygen to form oxides. Metal oxides are alkaline and oxides of non-metals are acidic in nature.
15. Metals react with water at different rates to form oxides and hydrogen gas. Non-metals do not react with water except sodium and magnesium.
16. Non-metals generally do not react with acids but metals react to produce hydrogen gas.
17. A more reactive metal displaces the less reactive metal from its compound in aqueous solution.
18. Metals and non-metals are very useful to us. They are used for different purposes.
19. All the materials can be divided into metals, non-metals and metalloids on the basis of above discussed physical mid chemical properties. Metalloids are those materials which possess the qualities of both metals and non-metals.

Haryana State Board HBSE 8th Class Science Solutions Chapter 3 Synthetic Fibres and Plastics Textbook Exercise Questions and Answers.

Haryana Board 8th Class Science Solutions Chapter 3 Synthetic Fibres and Plastics

HBSE 8th Class Science Synthetic Fibres and Plastics Textbook Questions and Answers

Question 1.
Explain why some fibres are called synthetic?
Answer:
Some fibres are called synthetic because they do not occur naturally and are made by man using petrochemicals.

Question 2.
Mark (✓) the correct answer:

Rayon is different from synthetic fibre because
(i) it has a silk like appearance
(ii) it is obtained from wood pulp
(iii) its fibres can also be woven like those of natural fibres.
Answer:
(ii) it is obtained from wood pulp. ✓

Question 3.
Fill in the blank with appropriate words:
(i) Synthetic fibres are also called ……………. or ……………. fibres.
(ii) Synthetic fibres are synthesised from raw material called ……………. .
(iii) Like synthetic fibres, plastic is also a ……………. .
Answer:
(i) man-made or artificial fibres
(ii) petrochemicals
(iii) polymer.

Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
Nylon fibres are very strong, thus they are used to prepare ropes for mountaineering. They are also used to prepare parachutes.

Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Advantanges of storing foods in plastic containers are:
(a) the plastics do not react with the food stored in them.
(b) the plastics are light weight and are strong.
(c) they are easy to handle and safe.

Question 6.
Explain the difference between the thermoplastic and thermosetting plastics.
Answer:
Differences between thermoplastic and thermosetting plastics:
(i) Thermoplastics can be mtelted on heating but thermosetting plastics Cannot be melted.
(ii) Thermoplastics can be reshaped as many times as desired but thermosetting plastics cannot.
(iii) Thermoplastics can be bent but thermosetting plastics cannot be bent.
(iv) Thermoplastics are good conductors of heat, thermosetting plastics are bad conductors of heat.

Question 7.
Explain why the following are made of thermosetting plastics:
(a) Saucepan handles
(b) Electric plugs/switches/plug boards.
Answer:
(a) The handles of saucepan are made of thermosetting plastic because it is a bad conductor of heat and do not get heated up while cooking. So it becomes easy to handle the utensil while cooking.
(b) Electric plugs/ switches and plug boards are made up of thermosetting plastic because it is a bad conductor of electricity. It does not allow the electric current to pass through it, thus safe in using in electric appliances.

Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Telephone instruments, toys, cooker handles, carry bags, ball point pens, plastic bowls, electric wire covering, plastic chairs, electrical switches.
Answer:
Can be Recycled: Toys, carry bags, plastic bowls, ball point pen, plastic chairs, electric wire covering.
Cannot be Recycled: Cooker handles, electric switches, telephone instruments.

Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
Cotton clothes are preferred to synthetic clothes in summers because cotton is a bad conductor of heat. It does not allow the outer heat to enter in our body, thus protects body from heat. It also has more capacity to hold moisture than the synthetic clothes. So, it retains
the sweat of the body and keeps it cool. So, Rana should buy shirts made upof cotton.

Question 10.
Give examples to show that plastics are noncorrosive in nature?
Answer:
Following examples show that plastics are non-corrosive in nature:
(i) They are used to store chemicals in laboratories.
(ii) They are used to store all types of food, as it does not react to materials stored in it.
(iii) It does not even react with air and water.

Question 11.
Should theiiandle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer:
No, the handle and bristles of a tooth brush should not be made of the same material because the bristles should be soft and the handle should be hard. So the bristles should be made up of soft material so that it does not harm the gums. The handles should be made up of hard material so that it can give firm grip.

Question 12.
‘Avoid plastics as far as possible,’ Comments on this advice.
Answer:
Plastics are harmful for our environment. Some of the plastics cannot be recycled, so they cannot be used again and thus cannot be finally disposed off. They thus, should be avoided as far as possible.

Question 13.
Match the terms of column I correctly with the phrases given in column II:

Answer:

Question 14.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Answer:
Manufacturing synthetic fibres is actually helping conservation of forests because it does not require cfutting plants and hunting animals to get the natural fibres. The synthetic fibres are made up of chemicals and these chemicals are not available in forests.

Question 15.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
Observe all the electric wires of your house from a distance. You can take an electric wire which is not carrying current. Open the main wire you will see three/two small wires in the main wire and will see that they have covering of red, green and yellow plastic covering. This proves that the thermoplastics are bad conductors of electricity.

Extended Learning – Activities And Projects

1. Have you heard of the campaign: “Say No To Plastics”. Coin a few ihore slogans of this kind. There are certain governmental and non-governmental organisations who educate general public on how to make a wise use of plastics and develop environment friendly habits. Find, out organisations in your area which are . carrying out awareness programmes. If there is none, form one. .
Answer:
For self attempt. .

2. Organise a debate in the school. The children may be given an option to rule play as manufacturers of synthetic fabrics or those of fabrics from natural sources. They ican then debate on the topic “My Fabric is Superior.”
Answer:
For self attempt.

3. Visit five families in your Neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them in term: of cost, durability and maintenance. Make a short report and submit it to your teacher.
Answer:
For self attempt.

4. Devise an activity to show that organic waste is biodegradable while plastic is not.
Answer:
Take some organe peels or peels of any fruit or vegetable. Now take any broken object of plastic.
Take two flower pots. In one pot dig a small pit and throw peels and cover it with mud. In second pot put the plastic and cover it with mud. Observe them after 5-10 day, and you will see that the peels have started decomposing and nothing has happened to plastic toy.

5. If you wish to know more about fibres and plastics and the products made from them, you may explore the following web sites:
• http://www.pslc.ws/macrog/index.htm
• http://www.edugreenteri.res.in/ exploresolwaste/types/htm
• http://www.nationalgeographic.com/ resouces/ngo/eduction/plastics
• http://www.packagingtoday.com/
• http://www.bbc.co.uk/schools.gcsebitesize/ design/textiles/fibresrev/html/

HBSE 8th Class Science Synthetic Fibres and Plastics Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Why do we wear clothes?
Answer:
We wear clothes to get protected from heat, cold and other outer conditions.

Question 2.
How many types of fibres are there?
Answer:
There are two types of fibres: Natural fibre and Synthetic fibres.

Question 3.
What are natural fibres?
Answer:
Fibres obtained from animals and plants are called natural fibres.

Question 4.
What are synthetic fibres?
Answer:
Fibres made of chemicals by the man are called synthetic fibres.

Question 5.
Name some natural fibres.
Answer:
Silk, wpol, cotton, jute, etc.

Question 6.
Name some synthetic fibres.
Answer:
Nylon, rayon, polyester, Acrylic.

Question 7.
What are polymers?
Answer:
Polymers are small jinits which combindfo make a synthetic fibre.

Question 8.
Name one natural polymer.
Answer:
Cellulose is a polyiper of cotton.

Question 9.
Which synthetic fibre is called synthetic silk?
Answer:
Rayon.

Question 10.
Which country discovered silk for the first time?
Answer:
China.

Question 11.
Which raw material is used to make rayon?
Answer:
Wood pulp.

Question 12.
Which raw material is used to make Nylon?
Answer:
Coal, water and air.

Question 13.
Name few items made from nylon.
Answer:
Socks, ropes, tents, sleeping bags, parachutes, etc.

Question 14.
Which is the strongest synthetic fibre?
Answer:
Nylon.

Question 15.
Which synthetic fibre can be stronger than a steel wire?
Answer:
Wire made of nylon.

Question 16.
Name a synthetic fibre which works like wool.
Answer:
Acrylic.

Question 17.
What happens when synthetic fibre is burnt?
Answer:
It starts melting.

Question 18.
What are petrochemicals?
Answer:
Petrochemicals are raw materials processed to make synthetic fibres.

Question 19.
Name a few properties of plastics.
Answer:
They can be moulded, recycled, reused and melted.

Question 20.
What use polythene is put to?
Answer:
Polythene is used to make carry bags.

Question 21.
What do we call the plastics which can be remoulded again and again?
Answer:
Thermoplastics.

Question 22.
What do we call the plastics, which cannot be remoulded and reused?
Answer:
Thermosetting plastics.

Question 23.
Why electric switches and plugs are made of plastics?
Answer:
They are resistant to electricity.

Question 24.
Which material is used to make non-stick utensils?
Answer:
Teflon.

Question 25.
Which material is used to make the handles of the cookware?
Answer:
Melamine.

Question 26.
What makes plastic a wonder material?
Answer:
Lightness, strength, durability and non-reactiveness.

Short Answer Type Questions

Question 1.
Distinguish between Natural fibre and Synthetic fibre.
Answer:
Natural fibres are obtained from natural resources like plants and animals e.g., cotton, jute, etc. are obtained from plants. Silk and wool are obtained from animals. Synthetic fibres are made from synthetic materials, like petrochemicals, e.g. Nylon, Terelene, acrylic etc.

Question 2.
Why silk is so costly?
Answer:
Silk is a natural fibre obtained from silk moth. It takes a lot of time and efforts to make silk. So, it costs high.

Question 3.
What is Polyester?
Answer:
Polyester is the word coined by joining ‘poly’ and ‘ester’. This synthetic fibre is made by joining many ester units. Ester is a chemical which causes smell in fruits.

Question 4.
What makes acrylic more popular than pure wool?
Answer:
Acrylic is a synthetic fibre. It resembles wool in looks and in qualities. Wool is expensive becuse it is obtained from natural sources but acrylic is cheaper and is available in vibrant colours. It is more durable than wool.

Question 5.
What is the main disadvantage of synthetic fibre?
Answer:
Synthetic fibres are good conductors of heat. They melt when heated. This causes a great danger for the user. In case the fibre catches fire while working in the kitchen, it will stick to the user’s body and will cause great damage to skin.

Question 6.
Which fibre will you prefer to get your raincoat stitched? Why?
Answer:
We will prefer synthetic fibre for getting our raincoat stitched because it will not absorb much amount of water and dispell it saving us from rain water. It will also dryup soon later.

Question 7.
How can polythene carry bags be harmful for animals?
Answer:
Polythene carry bags are thrown here and there after using them. Stray cattle consume them. In this case, it can choke the respiratory system and damage their stomach. It can even cause their death.

Question 8.
What are thermoplastics? Explain with examples.
Answer:
Those plastics which can melt on heating and which can be reshaped on moulding again and again are called thermoplastics P.V.C., Polythene are examples of thermoplastics. Toys, containers, car grills, combs etc. are made with thermoplastics.

Question 9.
What are thermosetting plastics?
Answer:
Thermosetting plastics are those plastics, which can be only moulded for once. They cannot be reshaped or reused because they do not get softened op heating. Bakelite, melamine etc. are examples of thermosetting plastics.

Question 10.
What are biodegradable and non-biodegradable materials?
Answer:
Biodegradable substances are those substances which can be decomposed by bacteria and other natural processes. Those substances which cannot be decomposed are called non-biodegradable substances. Plastics are non-biodegradable.

Long Answer Type Questions

Question 1.
Distinguish between natural fibres and synthetic fibres.
Answer:

Question 2.
Name different artificial fibres and write their uses.
Answer:
Following are the main synthetic fibres:
(i) Rayon:
It is also called the artificial silk as it has great lustre and is fight in weight. It is obtained by the chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It is used as dress material. Mixed with cotton, it is used to make curtains, bedsheets etc. It is mixed with wool to make beautiful carpets.

(ii) Nylon:
It is the strongest fibre. It is made by coal, water and air. It is elastic in nature and fight in weight. It is lustrous and thus ideal for making dresses. It is also used to make stockings, seat belts, ropes, tents, toothbrushes, sleeping bags, curtains and parachutes, etc.

(iii) Polyester:
It is made up of multiple units of ‘esters’. The clothings made of this fibre do not get wrinkled easily. It is always crisp and easily washable. PET is also derived from polyester which ip turn is used to make containers, utensils, films, wires etc.

(iv) Acrylic: Acrylic is just like wool and is used to make sweaters and suit lengths.

Question 3.
Describe the characteristic features of the synthetic fibres.
Answer:
Synthetic fibres are made from chemical substances. Their qualities are quite different from those of natural fibres. Following are the characteristic features of the synthetic fibres:
1. Raw material: All synthetic fibres are made from chemicals. They are prepared by a number of processes using raw materials of petroleum family called petrochemicals.

2. Strength: Synthetic fibres are quite strong. Nylon is the strongest known fibre.

3. Durability: Synthetic fibres are quite durable. They do not wither easily. They are so strong and durable that ropes and parachutes etc. are made by using synthetic fibres.

4. Soak less water: Synthetic fibres absorb small quantities of water and loose it quick, so they dry up very soon.

5. Availability and cost: Synthetic fibres are less expensive and readily available. That makes it a popular dress material.

Question 4.
What are plastics? How many types of plastics are available? Explain.
Answer:
Plastics are synthetic materials which can be moulded to give any desirable shape. Plastics are two types:
Thermoplastics: Those plasties which can be melted and reshaped again and again to give any shape on heating are called thermoplastics. Thermoplastics can be reused as many times as desirable e.g. PVC and polythene.

Thermosetting Plastics are those plastics which can be melted on heating mid cannot be reshaped again and again. Melamine, Bakelite etc. are examples of thermosetting plastics.

Question 5.
Write the characteristic features of plastics.
Answer:
Plastic is a wonder material. Following characteristic features make it a common and popular choice:
(i) Plastics are light in weight so they are easy to handle and manage.
(ii) Plastics are strong and durable so they are used to make buckets, mugs, ropes, etc.
(iii) Plastics are non-reactive as they do not get corroded when they come in contact with other materials or substances. This property make them perfect for storing food items and chemicals.
(iv) Plastics are poor conductors of electricity. They do not allow the electric current to pass through them easily. They are, therefore, used to make coverings of electric wires and other electric appliances.

Question 6.
Write advantages and disadvantages of synthetic fabrics.
Answer:
Following are the advantages of synthetic fabrics:
(a) Most of the synthetic fibres are wrinkle resistant. They do not get wrinkled easily. They easily retain their original shape, if they get wrinkled. So it is convenient to wash and wear.
(b) Synthetic fibres are strong so they can take up heavy loads easily. They have got high tensile strength, which enables them to carry weights.
(e) They have great elasticity. They can be easily streched.
(d) Synthetic fibres are generally soft, so they are used to make variety of clothes and clothing materials.

Disadvantages:
(a) Synthetic fibres cannot absorb moisture. This makes them unsuitable to be warm during summers. When our body sweatsv This make body sticky and irritates the skin
(b) They are dangerous to be worn near fire or heat, as they easily catch fire and is unfit to he worn.
(c) They cannot be easily ironed as they melt very easily.

Question 7.
How disposal of plastic is a problem? Explain.
Answer:
Plastic is wonderful synthetic material which is very useful. But biggest disadvantage of plastic is its disposal. Plastic is a non- biodegradable subtance, which do not get decomposed on its own by other microorganisms. So, accumulation of plastic is causing great danger for environment in the following ways:
(i) We throw plastics openly on roadsides and streets. This provide home to many disease causing germs.
(ii) Plastics if burned in the soil create more problem. They cannot be decomposed and prevents the water from seeping into the soil. This affects the plants adversLy. Water gets accumulated on the soil and cause muddy pubbles.
(iii) Buring the plasties produce toxic gases alongwith smoke which cause air pollution. Such an air is unfit for consumption and give birth to many respiratory problems in animals.
(iv) Plastic waste when dumped in water, cause water pollution. Aquatic animals consume these toxic plastics and die. It can also cause reproductive problems in aquotic animals.

Synthetic Fibres and Plastics Class 8 HBSE Notes

1. All the clothes we wear are made up of fabrics. Fabrics in turn are made up of fibres. Fibres can be of two types: natural fibre and manmade or synthetic fibres.
2. Natural fibres are those fibres which we get from plants and animals e.g. cotton, wool, silk, jute, etc.
3. Artificial or synthetic fibres are made up of the chemical substances by processing in factories and mills.
4. A synthetic fibre is chain of small units, woven together to form a long chain. These chemical substances or this chain of small units is called a polymer. All synthetic fhbrics are made up of these repeating units called polymers.
5. Rayon, Nylon, polyester etc. are examples of the manmade fibres.
6. These synthetic fibres are used for many other purposes, except making clothes. Nylon is a very strong fibre. It is used to make parachutes, socks, ropes, toothbrushes, sleeping bags and other drappery accessories.
7. Synthetic fibres are stronger than natural fibres. They absorb lesser amount of water than, the natural fibres. That is why raincoats etc. are made up of the synthetic fibres. They get dry! very soon and need less care and maintenance.
8. Plastics are synthetic materials which are used for many purposes. We can see objects made up of plastics all around us.
9. Plastics are also made up of polymers. Plastics can be moulded, melted and recycled. But all plastics are hot same.
10. Plastics are of two types: Plastics which can be melted, reshaped, bent easily are known as thermoplastics. The plastics which cannot be melted or reshaped are called thermosetting plastics.
11. Thermoplastics are used to make toys, combs, containers, etc. P.V.C. is an example of thermoplastic.
12. Thermosetting plastics are poor conductors of heat and are resistant to electricity. So they are used to make handles of utensils, electric plugs and switches, etc.
13. Plastics are very useful for us in every sphere of life. But they do have their disadvantages too.
Plastics are non-biodegrada,ble, so we cannot get rid of waste plastic easily. It is causing threat to our environment.
14. Environment friendly habbits like Reduce, Reuse, Recycle and Recovery of plastics can help in saving Environment.

Haryana Board HBSE 8th Class Social Science Solutions

HBSE 8th Class Social Science Solutions in Hindi Medium

HBSE Class 8 Social Science History: Our Pasts – III (इतिहास – हमारे अतीत – III)

• Chapter 1 कैसे, कब और कहाँ
• Chapter 2 व्यापार से साम्राज्य तक कंपनी की सत्ता स्थापित होती है
• Chapter 3 ग्रामीण क्षेत्र पर शासन चलाना
• Chapter 4 आदिवासी, दीकु और एक स्वर्ण युग की कल्पना
• Chapter 5 जब जनता बगावत करती है (1857 और उसके बाद)
• Chapter 6 उपनिवेशवाद और शहर
• Chapter 7 बुनकर, लोहा बनाने वाले और फैक्ट्री मालिक
• Chapter 8 देशी जनता को सभ्य बनाना राष्ट्र को शिक्षित करना
• Chapter 9 महिलाएँ, जाति एवं सुधार
• Chapter 10 दृश्य कलाओं की बदलती दुनिया
• Chapter 11 राष्ट्रीय आंदोलन का संघटन : 1870 के दशक से 1947 तक
• Chapter 12 स्वतंत्रता के बाद भारत

HBSE Class 8 Social Science Geography: Resources and Development (भूगोल – संसाधन एवं विकास)

• Chapter 1 संसाधन
• Chapter 2 भूमि, मृदा, जल, प्राकृतिक वनस्पति और वन्य जीवन संसाधन
• Chapter 3 खनिज और शक्ति संसाधन
• Chapter 4 कृषि
• Chapter 5 उद्योग
• Chapter 6 मानव संसाधन

HBSE Class 8 Social Science Civics: Social and Political Life – III (नागरिक शास्त्र – सामाजिक एवं राजनीतिक जीवन – III)

• Chapter 1 भारतीय संविधान
• Chapter 2 धर्मनिरपेक्षता की समझ
• Chapter 3 हमें संसद क्यों चाहिए?
• Chapter 4 कानूनों की समझ
• Chapter 5 न्यायपालिका
• Chapter 6 हमारी आपराधिक न्याय प्रणाली
• Chapter 7 हाशियाकरण की समझ
• Chapter 8 हाशियाकरण से निपटना
• Chapter 9 जन सुविधाएँ
• Chapter 10 कानून और सामाजिक न्याय

HBSE 8th Class Social Science Solutions in English Medium

Haryana Board HBSE 8th Class Social Science Solutions Geography: Resources and Development

• Chapter 1 Resources
• Chapter 2 Land, Soil, Water, Natural Vegetation and Wildlife Resources
• Chapter 3 Mineral and Power Resources
• Chapter 4 Agriculture
• Chapter 5 Industries
• Chapter 6 Human Resource

Haryana Board HBSE 8th Class Social Science Solutions History: Our Pasts – III

• Chapter 1 How, When and Where
• Chapter 2 From Trade to Territory: The Company Establishes Power
• Chapter 3 Ruling the Countryside
• Chapter 4 Tribals, Dikus and the Vision of a Golden Age
• Chapter 5 When People Rebel 1857 and After
• Chapter 6 Colonialism and the City: The Story of an Imperial Capital
• Chapter 7 Weavers, Iron Smelters and Factory Owners
• Chapter 8 Civilising the Native, Educating the Nation
• Chapter 9 Women, Caste and Reform
• Chapter 10 The Changing World of Visual Arts
• Chapter 11 The Making of the National Movement: 1870s–1947
• Chapter 12 India After Independence

Haryana Board HBSE 8th Class Social Science Solutions Civics: Social and Political Life – III

• Chapter 1 The Indian Constitution
• Chapter 2 Understanding Secularism
• Chapter 3 Why Do We Need A Parliament?
• Chapter 4 Understanding Laws
• Chapter 5 Judiciary
• Chapter 6 Understanding Our Criminal Justice System
• Chapter 7 Understanding Marginalisation
• Chapter 8 Confronting Marginalisation
• Chapter 9 Public Facilities
• Chapter 10 Law and Social Justice

Haryana State Board HBSE 8th Class Maths Solutions Chapter 10 ठोस आकारों का चित्रण Intext Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 10 ठोस आकारों का चित्रण Intext Questions

(इन्हें कीजिए – पृष्ठ 163-164)

प्रश्न 1.
निम्नलिखित का मिलान कीजिए (आपके लिए, पहला मिलान किया हुआ है)-
हल:
मिलान निम्न प्रकार है-

(पृष्ठ 164-165)

प्रश्न 1.
निम्नलिखित चित्रों (वस्तुओं) का उनके आकारों से मिलान कीजिए-
हल :
मिलान निम्न प्रकार है-

(पृष्ठ 166)

प्रश्न 1.
अपने आस-पास की विभिन्न वस्तुओं को विभिन्न स्थितियों से देखिए। अपने मित्रों के साथ उनके विभिन्न दूश्यों की चर्चा कीजिए।
संकेत- कुछ चात्र ग्रुप बनाकर स्वयं अवलोकन करें।

(पृष्ठ 175)

प्रश्न 1.
निम्नलिखित बहुफलकों के लिए फलकों (faces), किनारों (edges) और शीर्षों (vertices) की संख्याओं को सारणीबद्ध कीजिए-(यहाँ V शीर्षों की संख्या, F फलकों की संख्या तथा E किनारों की संख्या प्रदर्शित करता है।)

आप अन्तिम दो स्तम्भों से क्या निष्कर्ष निकालते हैं? क्या प्रत्येक स्थिति में आप F + V = E + 2, अर्थात् F + V – E = 2 प्राप्त करते हैं? यह सम्बन्ध ऑयलर सूत्र (Euler’s Formula) कहलाता है। वास्तव में यह सूत्र प्रत्येक बहुफलक के लिए सत्य है।
हल:
निम्नलिखित बहुफलकों के लिए फलकों की संख्या (F), किनारों की संख्या (E) तथा शीर्षों की संख्या (V) को सारणीबद्ध करने पर,

अन्तिम दो स्तम्भों से प्रत्येक स्थिति में हमें F + V= E + 2, या F + V – E = 2 प्राप्त होता है। इस समीकरण को ऑयलर का सूत्र कहते हैं। तथा यह सूत्र बहुफलक के लिए सत्य है।

(सोचिए, चर्चा कीजिए और लिखिए – पृष्ठ 175)

प्रश्न 1.
यदि किसी ठोस में से कोई टुकड़ा काट दिया जाए, तो F, V और E में क्या परिवर्तन होता है? (प्रारम्भ करने के लिए, एक प्लास्टिसीन का घन लीजिए तथा उसका एक कोना काटकर इसकी खोज कीजिए।)
हल:
माना कि ABCDHEFG एक प्लास्टिसीन का घन है। इसमें से एक टुकड़ा PQR काट लिया जाता है। यहाँ PQR क्रमशः किनारा FG, FE तथा FB पर हैं। दी गई आकृति से,

स्थिति I :
घन ABCDHEFG में,
फलकों की संख्या (F) = 6
शीर्षों की संख्या (V) = 8
किनारों की संख्या (E) = 12
स्पष्टतः F + V = E + 2 = 6 + 8 – 12
= 2
इस प्रकार ऑयलर सूत्र सत्यापित होता है।

स्थिति II :
जब तल PQR घन में से काटकर निकाल दिया ता है, तब
फलकों की संख्या F = 7
शीर्षों की संख्या V = 10
किनारों की संख्या E = 15
स्पष्टतः F + V = E + 2 = 7 + 10 = 15
इस प्रकार, इस स्थिति में भी ऑयलर का सूत्र सत्यापित होता है।

Haryana State Board HBSE 8th Class Maths Solutions Chapter 9 बीजीय व्यंजक एवं सर्वसमिकाएँ Ex 9.5 Textbook Exercise Questions and Answers.

Haryana Board 8th Class Maths Solutions Chapter 9 बीजीय व्यंजक एवं सर्वसमिकाएँ Ex 9.5

प्रश्न 1.
निम्नलिखित गुणनफलों में से प्रत्येक को प्राप्त करने के लिए उचित सर्वसमिका का उपयोग कीजिए
(i) (x + 3) (x + 3)
(ii) (2y + 5) (2y + 5)
(iii) (2a – 7) (2a – 7)
(iv) (3a – \(\frac{1}{2}\))(3a – \(\frac{1}{2}\))
(v) (1.1m – 0.4) (1.1m + 0.4)
(vi) (a² + b²) (-a² + b²)
(vii) (6x- 7) (6x + 7)
(viii) (-a + c) (-a + c)
(ix) \(\left(\frac{x}{2}+\frac{3 y}{4}\right)\) \(\left(\frac{x}{2}+\frac{3 y}{4}\right)\)
(x) (7a – 9b) (7a – 9b).
हल:
(i) (x + 3) (x + 3)
सर्वसमिका, (a + b)² = a² + 2ab + b²
अत: (x + 3) (x + 3) = (x + 3)²
= x² + 2 × 3 × x +3 × 3
= x² + 6x + 9.

(ii) (2y + 5) (2y + 5)
= (2y + 5)²
= (2y)² + 2 × 2y × 5 + (5)²
= 4y² + 20y + 25.

(iii) (2a – 7) (2a – 7)
= (2a – 7)²
सर्वसमिका, (a – b)² = a² – 2ab + b²
= (2a)² – 2 × 2a × 7 + (7)²
= 4a² – 28a+ 49.
अत: (2a – 7) (2a – 7) = 4a² – 28a+ 49.

(iv) (3a – \(\frac{1}{2}\))(3a – \(\frac{1}{2}\))
= \(\left(3 a-\frac{1}{2}\right)^{2}\)
= (3a)² – 2 × 3a × \(\frac{1}{2}\) + (\(\frac{1}{2}\))²
= 9a² – 3a + \(\frac{1}{4}\)
अत: (3a – \(\frac{1}{2}\))(3a – \(\frac{1}{2}\)) = 9a² – 3a + \(\frac{1}{4}\)

(v) (1.1m -0.4) (1.1m + 0.4)
सर्वसमिका, (a + b) (a – b) = a² – b² से-
= (1.1m)² – (0.4)²
= 1.21m² – 0.16.

(vi) (a² + b²) (-a² + b²)
= (a² + b²) (b² – a²)
= (b² + a²) (b² – a²)
= (b²)² – (a²)² – b⁴ – a⁴.

(vii) (6x – 7) (6x + 7)
= (6x)² – (7)²
= 36x² – 49.

(viii) (-a + c) (-a + c)
= (c -a) (c- a)
= (c – a)²
= (c)² – 2ac + (a)²
= c² – 2ac + a²

(ix)

(x) (7a – 9b) (7a – 9b)
= (7a – 9b)²
= (7a)² – 2 x 7a x 9b + (9b)²
= 49a² – 126ab + 81b².

प्रश्न 2.
निम्नलिखित गुणनफलों को ज्ञात करने के लिए, सर्वसमिका (x + a) (x + b) = x² + (a + b) x + ab का उपयोग कीजिए-
(i) (x + 3) (x + 7)
(ii) (4x + 5) (4x + 1)
(iii) (4x – 5)(4x – 1)
(iv) (4x + 5)(4x – 1)
(v) (2x + 5y) (2x + 3y)
(vi) (2a² + 9) (2a² + 5)
(vii) (xyz – 4) (xyz – 2).
हल:
(i) (x + 3) (x + 7)
= x² + (3 + 7)x + 3 × 7
= x² + 10x + 21.

(iii) (4x + 5) (4x + 1)
= (4x)² + (5 + 1)4x + 5 × 1
= 16x² + 6 × 4x + 5.
= 16x² + 24x + 5.

(iii) (4x – 5) (4x – 1)
सर्वसमिका, (x – a) (x – b) = x² – (a + b) x + ab
= (4x)² – (5 + 1)4x + (-5) × (- 1)
= 16x² – 6 × 4x + 5.
= 16x² – 24x + 5.

(iv) (4x + 5) (4x – 1)
सर्वसमिका, (x + a) (x + b) = x² + (a + b) x + ab से-
(4x + 5) (4x – 1) = (4x)² + (5 – 1) 4x – 5 × (+1)
= 16x² + 4 × 4x – 5.
= 16x² + 16x – 5.

(v) (2x + 5y) (2x + 3y)
= (2x)² + (5y + 3y)x + 5y × 3y
= 4x² + 8y × 2x + 15y²
= 4x² + 8xy + 15y².

(vi) (2a² + 9) (2a² + 5)
= (2a²)² + (9 + 5)2a² + 9 × 5
= 4a⁴ + 14 × 2a² + 45.
= 4a⁴ + 28a² + 45.

(vii) (xyz – 4) (xyz – 2)
= (xyz)² – (4 + 2) xyz + 4 × 2
= x²y²z² – 6xyz + 8.

प्रश्न 3.
सर्वसमिका का उपयोग करते हुए निम्नलिखित वर्गों को ज्ञात कीजिए
(i) (b – 7)²
(ii) (xy + 3z)²
(iii) (6x² – 5y)²
(iv) (\(\left(\frac{2}{3}m+\frac{3}{2}\right)\))²
(v) (0.4p – 0.5q)²
(vi) (2xy + 5y)²
हल:
(i) (b – 7)²
= b² – 2b × 7 + 7²
= b² – 14 b + 49.

(ii) (xy + 3z)²
= (xy)² + 2 × xy × 3z + (3z)²
= x²y² + 6xyz² + 9z².

(iii) (6x² – 5y)²
= (6x²)² – 2 × 6x² × 5y + (5y)²
= 36x⁴ – 60x²y + 25y².

(iv) (\(\left(\frac{2}{3}+\frac{3}{2}\right)\))²
= (\(\frac{2}{3}\)m)² + 2 × \(\frac{2}{3}\)m × \(\frac{1}{5}\)n + (\(\frac{3}{2}\)n)²
= \(\frac{4}{9}\)m² + 2mn + \(\frac{9}{4}\)n²

(v) (0.4p – 0.5q)²
= (0.4p)² – 2 × 0.4p × 0.5q + (0.5q)²
= 0.16p² – 0.4pq + 0.25q².

(vi) (2xy + 5y)²
= (2xy)² + 2 × 2xy × 5y + (5y)²
= 4x²y² + 20xy² + 25y².

प्रश्न 4.
सरल कीजिए-
(i) (a² – b²)²
(ii) (2x + 5)² – (2x – 5)²
(iii) (7m – 8n)² + (7m + 8n)²
(iv) (4m + 5n)² + (5m + 4n)²
(v) (2.5p – 1.5q)² – (1.5p – 2.5q)²
(vi) (ab + bc)² – 2ab²c
(vii) (m² – n²m)² + 2m³n².
हल:
(i) (a² – b²)²
= (a²)² – 2 × a² × b² + (b²)²
(सर्वसमिका, (a – b)² = a² – 2ab + b²)
= a⁴ – 2a²b² + b⁴.

(ii) (2x + 5)² – (2x – 5)²
= [(2x)² + 2 × 2x × 5 + (5)²] – [(2x)² – 2 × 2x × 5 + (5)²]
= (4x² + 20x + 25) – (4x² – 20x + 25)
= 4x² + 20x + 25 – 4x² + 20x – 25
= 40x

(iii) (7m – 8n)² + (7m + 8n)²
= [(7m)² – 2 × 7m × 8n + (8n)²] – [(7m)² + 2 × 7m × 8n + (8n)²]
= 49m² – 112mn + 64n² + 49m² + 112mn + 64n²
= 98m² + 128n²

(iv) (4m + 5n)² + (5m + 4n)²
= (4m)² + 2 × 4m × 5n + (5n)² + (5m)² + 2 × 5m × 4n + (4n)²
⇒ 16m² + 40mn + 25n² + 25m² + 40mn + 16n²
⇒ 41m² + 80mn + 41n²

(v) (2.5p – 1.5q)² – (1.5p – 2.5q)²
सर्वसमिका, (a – b)² = a² – 2ab + b²से-
= [(2.5p)² – 2 × 2.5p × 1.5q + (1.5q)²] – [(1.5p)² – 2 × 1.5p × 2.5q + (2.5q)²]
= 6.25p² – 0.75pq + 2.25q² – [2.25p² – 0.75pq + 6.25q²]
= 6.25p² – 0.75pq + 2.25q² – 2.25p² + 0.75pq – 6.25q²
= 4p² – 4q²

(vi) (ab + bc)² – 2ab²c
= (ab)² + 2 × ab × bc + (bc)² – 2ab²c
= a²b² + 2ab²c + b²c² – 2ab²c
= a²b² + b²c².

(vii) (m² – n²m)² + 2m³n²
= (m²)² – 2 × m² × n²m + (n²m)² + 2m³n²
= m⁴ – 2m³n² + m²n⁴ + 2m³n²
= m⁴ + m²n⁴.

प्रश्न 5.
दराईए कि-
(i) (3x + 7)² – 84x = (3x – 7)²
(ii) (9p – 5q)² + 180pq = (9p + 5q)²
(iii) \(\left(\frac{4}{3} m-\frac{3}{4} n\right)\)² + 2mn = \(\frac{16}{9}\)m² + \(\frac{9}{16}\)n²
(iv) (4pq + 3q)² – (4pq – 3q)² = 48pq²
(v) (a – b) (a + b) + (b – c) (b + c) + (c – a) (c + a) = 0.
हल:
(i) (3x + 7)² – 84= (3x – 7)²
L.H.S. = (3x + 7)² – 84
= (3x)² + 2 × 3x × 7 + (7)² – 84x
= 9x² + 42x + 49 – 84x
= 9x² – 42x + 49
= (3x)² – 2 × 3x × 7 + (7)²
= (3x – 7)²
= R.H.S.

(ii) (9p – 5q)² + 180pg = (9q + 5q)²
L.H.S. = (9p – 5q)² + 180pg
= [(9p)² + 2 × 9p × 5q + (5q)²] + 180pg
= 81p² – 90pq + 25q² + 180pq
= 81p² + 90pq + 25q²
= (9p)² + 2 × 9p × 5q + (5q)²
= (9p + 5q)²
= R.H.S.

(iii)

(iv) (4pq + 3q)² – (4pq – 3q)² = 48pq²
L.H.S. = (4pq + 3q)² – (4pq – 3q)²
= [(4pq)² + 2 × 4pq × 3q + (3q)²] – [(4pq)² + 2 × 4pq × 3q + (3q)²]
= (16p²q² + 24pq² + 9q²) – (16p²q² – 24pq² + 9q²)
= (16p²q² + 24pq² + 9q²) – 16p²q² + 24pq² – 9q²)
= 48pq²
= R.H.S.

(v) (a – b) (a + b) + (b – c) (b + c) + (c – a) (c + a) = 0.
L.H.S. = (a – b) (a + b) + (b – c) (b + c) + (c – a) (c + a)
= a² – b² + b² – c² + c² – a²
= 0
= R.H.S.

प्रश्न 6.
सर्वसमिकाओं के उपयोग से निम्नलिखित मान ज्ञात कीजिए-
(i) (71)²
(ii) (99)²
(iii) (102)²
(iv) (998)²
(v) (5.2)²
(vi) 297 × 303
(vii) 78 × 82
(viii) (8.9)²
(ix) 10.5 × 9.5
हल:
(i) (71)²
= (70 + 1)²
= (70)² + 2 × 70 × 1 + (1)²
= 4900 + 140 + 1
⇒ 5041.

(ii) (99)²
= (100 – 1)²
= (100)² – 2 × 100 × 1 + (1)²
= 10000 – 200 + 1
= 9801

(iii) (102)²
= (100 + 2)²
= (100)² + 2 × 100 × 2 + (2)²
= 10000 + 400 + 4
= 10404.

(iv) (998)²
= (1000 – 2)²
= (1000)² – 2 × 1000 × 2 + (2)²
= 1000000 – 4000 + 4
= 996004.

(v) (5.2)²
= (5 + 0.2)²
= (5)² + 2 × 5 × 0.2 + (0.2)²
= 25 + 2.0 + 0.04
= 27 + 0.04
= 27.04.

(vi) 297 × 303
= (300 – 3) (300 + 3)
= (300)² – (3)²
= 90000 – 9
= 89991

(vii) 78 × 82
= (80 – 2) (80 + 2)
= (80)² – (2)²
= 6400 – 4
= 6396.

(viii) (8.9)²
= (9 – 0.1)²
= (9)² – 2 × 9 × 0.1 + (0.1)²
= 81 – 1.8 + 0.01
= 81.01 – 1.8
= 79.21.

(ix) (10.5) × (9.5)
= (10 + 0.5) (10 – 0.5)
= (10)² – (0.5)²
= 100 – 0.25
= 99.75.

प्रश्न 7.
a² – b² = (a + b) (a – b) का उपयोग करते हुए निम्नलिखित मान ज्ञात कीजिए-
(i) (51)² – (49)²
(ii) (1.02)² – (0.98)²
(iii) (153)² – (147)²
(iv) (12.1)² – (7.9)²
हल:
(i) (51)² – (49)²
= (51 + 49) (51 – 49)
= 100 × 2 ⇒ 200.

(ii) (1.02)² – (0.98)²
= (1.02 + 0.98) (1.02 – 0.98)
= 2.00 × 0.04 ⇒ 0.08.

(iii) (153)² – (147)²
= (153 + 147) (153 – 147)
= 200 × 6 ⇒ 1200.

(iv) (12.1)² – (7.9)²
= (12.1 + 7.9) (12.1 – 7.9)
= 20.0 × 4.2 = 84.0 ⇒ 84.

प्रश्न 8.
(x + a) (x + b) = x² + (a + b)x + ab का उपयोग करते हुए निम्नलिखित मान ज्ञात कीजिए
(i) 103 × 104
(ii) 5.1 × 5.2
(iii) 103 × 98
(iv) 9.7 × 9.8.
हल:
(i) 103 × 104
= (100 + 3) (100 + 4)
= (100)² + (3 + 4) × 100 + 3 × 4
= 10000 + 700 + 12
= 10712.

(ii) 5.1 × 5.2
= (5 + 0.1) (5 + 0.2)
= 5² + (0.1 + 0.2) × 5 + (0.1 × 0.2)
= 25 + 0.02 × 5 + 0.02
= 25 + 0.10 + 0.02
= 25.12.

(iii) 103 × 98
= (100 + 3) (100 – 2)
= (100)² + (3 – 2) × 100 + 3 × (-2)
= 10000 + 100 – 6
= 10094.

(iv) 9.7 × 9.8
= (9 + 0.7)(9 + 0.8)
= (9)² + (0.7 + 0.8)(9) + (0.7)(0.8)
= 81+ 13.5 + 0.56
= 95.06