Class 7

Haryana State Board HBSE 7th Class Science Solutions Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 6 Physical and Chemical Changes

HBSE 7th Class Science Physical and Chemical Changes Textbook Questions and Answers

Question 1.
Classify the changes involved in the following processes as physical or chemical changes.
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food.
Answer:
Physical Change (b), (d), (e)
Chemical Change (a), (c), (f)

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
(a) Cutting a log of wood into pieces is a chemical change.
(b) Formation of manure from leaves is a physical change.
(c) Iron pipes coated with zinc do not get rusted easily.
(d) Iron and rust are the same substances.
(e) Condensation of steam is not a chemical change.
Answer:
(a) False
(b) False
(c) True
(d) True
(e) True.

Question 3.
Fill the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of ………….. .
(b) The chemical name of baking soda is ……………… .
(c) Two methods by which rusting of iron can be prevented are …………. and …………. .
(d) Changes in which only …………. properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called …………. changes.
Answer:
(a) Calcium carbonate
(b) Sodium hydrogen carbonate
(c) Coating, galvanization
(d) Physical
(e) Chemical.

Question 4.
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas carbon dioxide.
lemon juice + baking soda → carbon dioxide + lime water
Since, a change in which one or more new substance are formed is called a chemical change, therefore this is a chemical change.

Question 5.
When a caùdie burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
Answer:
Physical Change → Melting of ware
Chemical Change → Burning of candle

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
The conversion of milk into curd, i.e., setting of curd is a permanent as well as irreversible and lead to the production of a new substance. The new substance, curd is formed has different composition and properties from the milk. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood is cutting it into small pieces are considered as two different types of a changes.
Answer:
Burning of wood is a chemical change because, in addition to new products burning is always accompanied by production of heat.
Cutting of wood into small pieces is a physical change because, pieces of wood underwent changes in size and no new substance is formed.

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Take a cup full of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling add copper sulphate powder slowly while stirring continuously. Continue adding copper sulphate powder till no more powder can be dissolved. Filter the solution. Allow it to cool. Do not disturb the solution when it is cooling. Look at the solution after some time. Now, you can see the crystals of copper sulphate.

Question 9.
Explain how painting of an iron gate prevents it from rusting.
Answer:
The process of rusting can be represented by the following equation:
Iron (Fe) + Oxygen (O₂ from the air) + Water (H₂O) → rust (iron oxide Fe₂O₃).

For rusting the presence of both oxygen and water (or water vapour) is essential. In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster. So, prevent iron gate from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease. In fact, these coats should be applied regularly to prevent rusting.

Question 10.
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
The water of coastal areas contain many salts. The salt water makes the process of rust formation faster. Thus, rusting of iron objects is faster in coastal areas than deserts.

Question 11.
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change,
(ii) Process – B is a chemical change.
(iii) Both process A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both process A and B are chemical changes.

Extended Learning – Activities And Projects

Question 1.
Take three glass bottles with wide mouths. Label them A, B and C. Fill about half of bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil of the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.
Answer:
Do yourself.

Question 2.
Prepare crystals of alum.
Answer:
Do yourself.

Question 3.
Collect information about the types of fuels used for cooking in your area. Discuss with your teachers/parents/others which fuels are less polluting and why.
Answer:
Do yourself.

HBSE 7th Class Science Physical and Chemical Changes Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is a physical change?
Answer:
Change in which no new product is formed.

Question 2.
What is a chemical change?
Answer:
A change in which a new substance with different properties is formed.

Question 3.
Which of the following substance contains only one kind of atoms?
copper, iron, iron sulphide, sulphur, oxygen gas, water, air and hydrogen gas.
Answer:
The following contains only one kind of atoms:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 4.
Which of the following substances are compounds and which are elements?
Magnesium oxide, Mercuric oxide, Carbon, Nitrogen, Potassium permagnate, Sodium carbonate.
Answer:
Elements: Carbon, nitrogen.
Compounds: Magnesium oxide, mercuric oxide, potassium permanganate, Sodium carbonate.

Question 5.
Write the symbol of the following elements:
Aluminium, calcium, chlorine, cobalt, iodine and mercury.
Answer:
Al, Ca, Cl, Co, I, Hg.

Question 6.
Ne is the symbol of neon. What else does it represent?
Answer:
This symbol represent one atom of Neon.

Question 7.
Which elements are represented by the following symbols?
Na, K, P, Pb, Ca, Zn, Br, Sn.
Answer:
Sodium, Potassium, Phosphorus, Calcium, Zinc, Bromine, Tin.

Question 8.
Name four Elements which occur in gaseous form.
Answer:
Oxygen, Nitrogen, Hydrogen and Argon.

Question 9.
When some one open a bottle of perfumes, you smell it from a distance why it is so?
Answer:
It is due to the property of gases that their molecules diffuse (move) easily in the air.

Question 10.
What is crystallisation?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called
crystallisation.

Question 11.
Define chemical reaction.
Answer:
The process in which the originally present substances change into new substances is called a chemical reaction.

Question 12.
What is matter?
Answer:
Anything which occupies space and has weight is called matter. Example: Air, Water, Wood, Stone, etc.

Question 13.
What are solids?
Answer:
Any materials which has a definite shape and definite volume, at room temperature is called solid.

Question 14.
What are liquids?
Answer:
Any substance which has a definite volume but no definite shape and has one free surface is called liquids: Milk, Water, Fruit juice, Alcohol etc.

Question 15.
Name two elements that are abundantly found in air.
Answer:
The two elements that are found abundantly in air are Nitrogen element and Oxygen element.

Question 16.
Choose the elements from the following substances: Marble, Mercury, Air, Carbon.
Answer:
Mercury and Carbon are elements.

Question 17.
What is the difference between 2N and N?
Answer:
2N represent 2 atoms of nitrogen and N represent 1 molecule of nitrogen.

Question 18.
Which of the following contains only one kind of atoms?
Copper, Iron sulphide, Sulphur, Oxygen gas, Water, Air and Hydrogen gas.
Answer:
Copper, Iron, Sulphur, Oxygen gas, Hydrogen gas.

Question 19.
Which of the following substances are compounds and which are elements?
Magnesium oxide, nitrogen, potassium permanganate, sodium carbonate.
Answer:
Compounds: Magnesium oxide, Potassium permanganate, Sodium carbonate.
Elements: Nitrogen.

Question 20.
Write down the chemical symbols of the following elements: Potassium, Calcium, Phosphorus, Nitrogen, Sulphur.
Answer:
K, Ca, P₄, N and Sg.

Question 21.
Write the names of the elements having the following symbols: C, Br, P, Al, Si.
Answer:
Carbon, Bromine, Phosphorus, Aluminium and Silicon.

Question 22.
A given substance ‘X’ has definite shape, fixed volume, is in comprissible and non-diffusing. What is the physical state of the substance ‘X’?
Answer:
The substance ‘X’ is solid state.

Question 23.
Write the names of the elements which compose a molecule of water.
Answer:
Hydrogen and Oxygen.

Question 24.
Name the three most abundant elements on the earth’s crust.
Answer:
Iron, Aluminium and Silicon.

Question 25.
Give the chemical formulae of the following:
(i) Calcium hydroxide
(ii) Copper oxide
(iii) Iron chloride
(iv) Zinc nitrate
(v) Silver sulphate
(vi) Lead carbonate
(vii) Potassium phosphate
(viii) Sodium hydroxide
(ix) Hydrochloric acid
(x) Zince hydroxide.
Answer:
(i) Ca(OH)₂
(ii) CuO
(iii) FeCl₂
(iv) Zn (NO₃)₂
(v) Ag₂SO₄
(vi) PbCO₃
(vii) K₃PO₄
(viii) NaOH
(ix) HCl
(x) Zn(OH)₂.

Question 26.
Define reactents.
Answer:
The original substances that take part in a chemical reaction are called the reactants,

Question 27.
Define products.
Answer:
The substances that form as a result of chemical reaction are called the products.

Question 28.
Define chemical combination reaction.
Answer:
When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.

Question 30.
Define chemical displacement reaction.
Answer:
When a more reactive element displaces a less reactive elements from its aqueous salt solution, the reaction which takes place is called chemical displacement.

Question 31.
What kind of chemical reaction takes place when a mixture of iron fillings are heated with sulphur?
Answer:
Chemical combination reaction.

Short Answer Type Questions

Question 1.
Formation of clouds is a physical change. Explain.
Answer:
Formation of clouds is a physical change. Clouds are formed by condensation of water vapours present in the atmosphere. When rainwater goes back on the earth no new product is formed. Therefore, it is a physical change.

Question 2.
Explosion of a cracker is a chemical change. Explain.
Answer:
When we burn a cracker, it exploide. Heat, light and smoke comes out after explosion. Many new products are formed. So, it is a chemical change.

Question 3.
Most physical changes are reversible. Give reasons with two examples.
Answer:
All physical changes are reversible. Because in physical changes, no new product is formed. They can be reversed easily.
Examples:
(i) Dissolving of sugar in water is a physical change and we get back sugar and water easily.
(ii) Formation of ice from water. In melting of ice, we can get water back.

Question 4.
Identify the type of change and state whether energy is evolved or absorbed in each one of the following:
Burning of a candle, lighting of a bulb, preparation of food by green plants, Volcanic eruption.
Answer:
(i) Burning of a candle: Chemical change, energy evolved.
(ii) Lighting of a bulb: Physical change, energy evolved.
(iii) Preparation of food by green plants: Chemical change, energy absorbed.
(iv) Volcanic eruption: Chemical change, energy evolved.

Question 5.
What is a chemical formula? What information does it provide?
Answer:
Chemical formula is a shorthand method of using symbols to represent the composition of a compound. Using it, we can get the following informations:
(i) Constituting name of the elements present in the compound, e.g., water has the formula H₂0. It shows that water is made up .. of two elements, hydrogen and oxygen.
(ii) Atoms present in each element, e.g.,
(iii) The composition of compound and the formula H₂O shows that in a molecule of molecular weight of the compound, this compound two atoms of hydrogen and one atom of oxygen are present.

Question 6.
What are the differences between chemical and physical changes?
Answer:
Differences between chemical and physical changes:

Chemical change	Physical change
1. A new substance is formed.	1. No new substance is formed.
2. It is a permanent change.	2. It is a temporary change.
3. The composition of new substances changes.	3. No change in the composition of change takes place.
4. It is irreversible.	4. It is reversible.
5. Heat/light evolved or absorbed during change.	5. No heat light evolved or absorbed or may be evolved or absorbed.

Question 7.
How is common salt obtained from sea water?
Answer:
In the coastal regions of India, especially in the Rann of Kutch in Gujarat and some parts of Tamil Nadu, the sea water is collected in shallow pits. It is then allowed to evaporate in the sun. As the water evaporates, the salt solution becomes supersaturated. This supersaturated solution cannot hold the excess salt. Thus, it separates out in form of salt crystals. These salt crystals are collected. They are redissolved in water and the solution is filtered to remove insoluble impurities. The clear solution is again evaporated so as to obtain the crystals of pure salt.

Question 8.
What is crystallisation? To what purpose is it put?
Answer:
The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called Crystallisation.

The process of crystallisation is employed for the separation of a pure water soluble substance from its mixture. For example, if there is a mixture of alum and common salt, the pure alum crystals can be separated by the process of crystallisation.

Question 9.
What is the significance of an equation?
Answer:
Significance of an equation:
(i) It tells us which substance reacted and which substances are produced.
(ii) It tells us the quantities of each of the reactants and each of the products.

Question 10.
Give four examples of a physical change.
Answer:
(i) Formation of dew.
(ii) Evaporation of water.
(iii) Melting of wax.
(iv) Making of ice-cream.

Question 11.
Give four examples of a chemical change.
Answer:
(i) Photosynthesis by plants.
(ii) Clotting of blood.
(iii) Curdling of milk.
(iv) Burning of candle.

Question 12.
State four characteristics of physical change.
Answer:
(i) It is temporary.
(ii) It is reversible.
(iii) No new substance is produced.
(iv) No change in the chemical properties.

Question 13.
State four characteristics of chemical change.
Answer:
(i) It is permanent.
(ii) It is irreversible.
(iii) New substance is produced.
(iv) Changes in the chemical properties due to the formation of new substances.

Question 14.
What happens when an iron blade of a knife is dipped in copper sulphate solution? What kind of chemical reaction takes place?
Answer:
When an iron blade of a knife is dipped in copper sulphate solution iron blade is coated with reddish deposit of copper. Thus, we can say that iron (more reactive element), displaces copper (less reactive element), from its aqueous copper sulphate solution. Chemical displacement reaction is takes place.

Question 15.
Why do the molecules in a liquid tend to stay together and give a condensed form?
Answer:
In a liquid, the molecular motion are not great enough to over come the force of attraction between molecules. That is why the molecules tend to stay together and give a condensed form.

Question 16.
On a hot summer day the cycle tubes burst suddenly. Explain why?
Answer:
The cycle tubes are filled with air. On a hot summer day, the temperature of the atmosphere is high. When cycle runs on the road, the friction between the cycle wheel and the path produces heat which raises the temperature of the air in the cycle tubes. On heating the air expands and exerts pressure in the inside of the tubes. Due to the pressure, the cycle burst suddenly on a hot summer day.

Question 17.
Why can the same substance exist in all the three states, that is, solid liquid and gas?
Answer:
The space between the molecules, the force of attraction between the molecules, and the amount of movement of the molecules of a substance can be changed by changing the pressure and temperature of the substance. So depending on the pressure and temperature, the same substance can exist in all the three states i.e., Solid, liquid and gaseous. For example under normal pressure water exists as a solid in the form of ice at a temperature of 0°C or below. It exists as a liquid in the form of water at the room temperature and as a gas in the form of steam at 100°C or above.

Question 18.
Write some important properties of an element.
Answer:
Properties of an element are:
(i) An element is made up of some kinds of atoms.
(ii) An element cannot be Broken up into much simpler substances,
(iii) An element can be represented by a chemical symbol.

Question 19.
What are the important characteristics of a compound?
Answer:
(i) Chemical compound is made up of two or more elements combined chemically.
(ii) They have fixed formula or composition.
(iii) They have fixed melting point (M.P.) and boiling point (B.P.).
(iv) Energy is either evolved or absorbed during formation of a compound.
(v) Properties of constituent elements are different from its compound, e.g., properties of water (H₂O) are different from properties of hydrogen and oxygen.

Question 20.
What does the formula CO₂ represent?
Answer:
Molecular formula CO₂ represents:
(i) the name of the compound carbon dioxide.
(ii) carbon dioxide is made up of two kinds of elements – carbon and oxygen.
(iii) one molecule of carbon dioxide has one atom of carbon and 2 atoms of oxygen.
(iv) the molecular mass of carbon dioxide is 12 + 2 x 16 = 44 gram.

Question 21.
How is salt obtained from sea-water?
Answer:
The seas are great sources of salts. A litre of a water contains about 35 grams of salts. Sodium chloride is the main salt. The sea-water is trapped in shallow called lagoons and is allowed to evaporate in sunlight to white solid crystal of salts. These crystals are processed and packed to send the markets.

Question 22.
Give three reasons for supporting that water is a compound and not a mixture.
Answer:
Water is considered a compound due to the following reasons:
(i) Water cannot be separated into its constituents, hydrogen and oxygen, by the physical process.
(ii) The properties of water are entirely different from those of its constituents hydrogen and oxygen.
(iii) Water contains hydrogen and oxygen combined together in a fixed proportions of 1:8 by weight.

Question 23.
Explain why solution of salt in water is considered a mixture and not a compound. Give three reasons.
Answer:
Salt solution is considered a mixture due to the following reasons:
(i) Salt solution can be separated into salt and water by the physical process.
(ii) Salt solution, shows the properties of both its constituents salt as well as water.
(iii) The composition of salt solution is variable i.e., the percentage of salt and water in different salt solutions are different.

Question 24.
What information do we get from a chemical equation?
Answer:
The informations obtained from a chemical equation are:
(i) Name of the substance (elements or compound) taking part in reaction, i.e., reactants and products.
(ii) The number of atoms and molecules of different substances.
(iii) The conditions under which the reaction takes place or taking part in reaction, for example:
N₂ + 3H₂ → 2NH₃
It represents 1 molecule of nitrogen combines with 3 molecules of hydrogen to form 2 molecules of ammonia.

Question 25.
“In a chemical reaction, there is only a rearrangement of the atoms of the reactants.” Explain this statement giving an example.
Answer:
In a chemical reaction, there is only a x’e. angement of the atoms of the reactants because when a chemical reaction occurs new products are formed. These products have same kind and number of atoms as are present in reactants. They are only rearrange to give new substances. For example, in a reaction between iron and sulphur to give iron sulphide the number of atoms of iron and sulphur are identical on both sides of the equation.
Fe + S → FeS (On heating)

Question 26.
What is done to make a chemical equation more informative?
Answer:
To make a chemical equation more informative it should be balanced and conditions of the reaction should be written above the arrow. For example,

It shows that 2 molecules of water on electrolysis break up into 2 molecules of hydrogen and 1 molecule of oxygen.

Question 27.
What do you understand by reactants and products?
Answer:
Reactants: Substances taking part in a reaction are called reactants. They are written on the left side of the chemical equation.
Products: Substances produced in a reaction are called products. They are written on the right side of the equation.
Example:

Long Answer Type Questions

Question 1.
What does a chemical formula represent?
Answer:
Significance of chemical formula:
(i) It represents the name of the substance.
(ii) It represents one molecule of the substance.
(iii) It gives the names of all the elements present in the molecule.
(iv) It represents the mass of one molecule.

As an example of the formula of H₂SO₄:
(i) Represents sulphuric acid.
(ii) Represent one molecule of sulphuric acid.
(iii) Tells that sulphuric acid contains three elements:
hydrogen, sulphur, and oxygen.
(iv) Tells that one molecule of sulphuric acid contains two atoms of hydrogen; 1 atom of sulphur and 4 atoms of oxygen.

Question 2.
What do you understand by the following terms? Give examples.
(i) Endothermic chemical change
(ii) Exothermic chemical change.
Answer:
(i) Endothermic chemical change: When a chemical change takes place with the absorption of heat energy, then the change is said to be endothermic. .
Examples: Heating of mercuric oxide to form mercury and oxygen. Heating of calcium carbonate to form calcium oxide and carbon dioxide.

(ii) Exothermic chemical change: When a chemical change takes place with the liberation of heat energy, the change is said to be exothermic.
Examples: Candle on burning liberates heat and light energy. Respiration is an exothermic change.

Question 3.
What is a compound? How does it differ from a mixture?
Answer:
A compound consists of two or more elements, joined together in a fixed ratio by chemical bonds. For example, water formed from hydrogen and oxygen, sodium chloride formed from sodium and chlorine, sugar formed from carbon, hydrogen and oxygen, nitre formed from potassium, nitrogen and oxygen are all compound.
Difference between compounds and mixtures:

Compound	Mixture
(i) A compound consists of only tne kind of chemical substance.	(i) A mixture consists of two or more chemically different substances.
(ii) The components of a compound cannot be separated by a simple means.	(ii) The composition of mixture can be separated easily by simple means.
(iii) Heat, light or electricity is absorbed or evolved during its formation.	(iii) Its formation is not accompanied by absorption or evolution of heat, light or electricity.
(iv) Compound has definite formula.	(iv) Mixture do not have definite formula.
(v) Compounds have definite M.P. and B.P. Compound is always homogeneous	(v) Mixture do not have fixed M.P. and B.P.

Question 4.
What is the difference between a balanced and unbalanced chemical equations? Explain with an example.
Answer:
Difference between a balanced and unbalanced chemical equations:
In unbalanced chemical equations, the number of each element atoms do not same. As for example:
Mg + O₂ → MgO.
This is not a balanced equation because the number of Mg atom and oxygen atoms are not same on both the sides, Le., reactants and product sides. On the other hand, in a balanced chemical equation the number of each atoms of each elements on both sides should be equal. As for example:
2Mg + O₂ → 2MgO.
In this balanced chemical equation the number of magnesium atoms and oxygen atoms in the left hand side are equal to the right hand side of the equation. So it is a balanced chemical equations.
(i) A mixture consists of two or more chemically different substances.
(ii) The composition of mixture can be separated easily by simple means.
(iii) Its formation is not accompanied by absorption or evolution of heat, light or electricity.
(iv) Mixture do not have definite formula.
(v) Mixture do not have fixed M.P. and B.P.
(vi) Mixture can be homogeneous and heterogenous.

Question 5.
Balance the following equations:
(i) Fe + O₂ → Fe₂O₃
(ii) H₂O + H₂ → O₂
(iii) Mg + O₂ → MgO
(iv) Al + O₂ → Al₂O₃
(v) Fe + HCl → FeCl₃ + H₂
(vi) Cu + O₂ → CuO
(vii) Hg + O₂ → HgO
(viii) Zn + HCl → ZnCl₂ + H₂
(xi) Al + HCl → AlCl₃ + H₂
(x) N₂ + H₂ → NH₃
Answer:
(i) 4Fe + 3O₂ → 2Fe₂O₃
(ii) 2H₂O → 2H₂ + O₂
(iii) 2Mg + O₂ → 2MgO
(iv) 4Al + 3O₂ → 2Al₂O₃
(v) 2Fe + 6HCl → 2FeCl₃ + 3H₂
(vi) 2Cu + O₂ → 2CuO
(vii) 2Hg + O₂ → 2HgO
(viii) Zn + 2HCl → ZnCl₂ + H₂
(xi) 2Al + 6HCl → 2AlCl₃ + 3H₂
(x) N₂ + 3H₂ → 2NH₃

Physical and Chemical Changes Class 7  HBSE Notes

1. Properties such as shape, size, colour and state of a substance are called its physical properties.
2. A change in which a substance undergoes a change in its physical properties is called a physical change. A physical change generally reversible.
3. A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction.
Some common examples of chemical change:
1. Burning of wood or charcoal.
2. Burning of Candle.
3. Decomposition of water into hydrogen and oxygen.
4. Formation of water from hydrogen and oxygen.
5. Digestion of food.
6. Curdling of milk.
7. Formation of biogas (Crobar gas).
8. Burning of petrol or diesel.
9. Smoking of cigarette.
10. Drying of paint.
11. Rusting of iron.
12. Ripening of fruit.
13. Baking of cake.
14. Photosynthesis by plants.
15. Formation of wine.

Some Common Examples of Physical Changes:
1. Formation of dew.
2. Evaporation of water.
3. Crystallisation of sugar from its solution.
4. Ringing of an electric bell.
5. Breaking of glass pane.
6. Making of ice-cream.
7. A rock rolling down a hill.
8. Bending of glass tube by heating.
9. Melting of wax.
10. Sublimation of camphor.

4. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting.
5. Any pure substance which cannot be broken into two or more pure substances by any chemical means is called an element.
6. The smallest unit of an element, which takes part in a chemical reaction is called an atom.
7. The smallest unit of a pure substance, which always exists independently and can retain physical and chemical properties of that substance, is called a molecule.
8. A metal is an element which is generally malleable, ductile and a good conductor of heat and electricity. About 80% of the elements are metals.
9. Non-metals are bad conductors of heat and electricity. They are neither malleable nor ductile. Non-rr Hals are generally soft.
10. When the molecule of a substance contains two or more atoms of different elements, combined together in a definite ratio, then it is said to be a molecule of a compound.
Symbols of common elements (Metals)

11. When one or more substances (elements or compounds) undergo a chemical change, with the absorption or release of energy, so as to form one or more new products, then the change taking place collectively is called chemical combination.
12. When two or more elements or compounds react chemically to form only one new product, then the reaction which takes place is called chemical combination.
13. When a single chemical compound decomposes on heating or by some other kind of energy, so as to form two or more new substances (elements or compounds), then the chemical reaction which takes place is called chemical decomposition.
14. When a more reactive element displaces a less reactive element from its aqueous salt solution, the reaction which takes place is called chemical displacement.
15. When an acid solution reacts with a base or metal carbonate, so as to form a salt, then the reaction is called neutralisation reaction.
16. The process of separation of pure crystals of a substance from its hot and supersaturated (concentrated) solution on cooling is called crystallisation.

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Haryana State Board HBSE 7th Class Science Solutions Chapter 5 Acids, Bases and Salts Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 5 Acids, Bases and Salts

HBSE 7th Class Science Acids, Bases and Salts Textbook Questions and Answers

Question 1.
State differences between acids and bases.
Answer:

Acids	Bases
1. A substance which dissolves in water to give hydrogen ions as the only positively charged ions is called an acid.	1. A substance which react with acids to form salt and water as only products is called a base.
2. They have a sour taste.	2. These have a better taste.
3. They turn blue litmus red.	3. Bases turn red litmus blue.

Question 2.
Ammonia is found is many household products, such as window cleaners. It turns red litmus blue, what is its nature?
Answer:
Basic.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper.

Question 4.
Is the distilled water acidic/basic/ neutral? How would you verify it?
Answer:
The distilled water is neutral. Put a drop of the distilled water on a strip of the red litmus paper with the help of a droper. We observe that colour of the litmus paper as not change.

The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.

Question 5.
Describe the proeess of neutralization with the help of an example.
Answer:
The process due to! which an acid completely reacts with a base to form salt and water as the only products is called neutralization.
Acid + Base → Salt + Water
Example: Hydrochloric add (HCl) + Sodium hydroxide (NaOH)
Sodium chloride (NaCl) + Water (H₂O)

Question 6.
Make “T” if the statement is true and ‘F’ if it is false.
(i) Nitric acid turn red litmus blue.
(ii) Sodium hydroxide turns blue litmus red.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.
(v) Tooth decay is caused by the presence of a base.
Answer:
(i) Flase
(ii) Flase
(iii) True
(iv) True
(v) True.

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink; How will Dorji decide which drink is to be served to whom?
Answer:
Do yourself.

Question 8.
Explain why?
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamane solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
(a) Our stomach contains hydrochloric acid. It help us to digest food. But too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

(b) The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains Zinc carbonate.

(c) The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you Identify them? You have only turmeric indicator.
Answer:
Do yourself.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The nature of the solution is neutral, because the solutions which do not change the colour of either red or blue litmus are known as neutral solution. These substances are neither acidic nor basic.

Question 11.
Consider the following statements:
(a) Acids and bases both change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?
(i) All four
(ii) a and b
(iii) b and c
(iv) only d
Answer:
(ii) a and b.

Extended Learning – Activities And Projects

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet’root. Explain how it works.
(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.)
Answer:
Do yourself.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and’ basic solutions with it. Present your observations in the form of a Table.
Answer:
Do yourself.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Answer:
Do yourself.

Question 4.
Visit a doctor. Find out the medicines be prescribes to treat acidity. Ask him how acidity can be prevented.
Answer:
Do yourself.

HBSE 7th Class Science Acids, Bases and Salts Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is an acid Id
Answer:
A substance which dissolves in water to give hydrogen ions as the only positively charged ions’fs called an acid.

Question 2.
What are mineral acids? Give, three examples.
Answer:
The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples: Sulphuric acid, Nitric acid, Hydrochloric acid.

Question 3.
What are organic acids? Give three examples.
Answer:
Organic acids are found in plant and animal products, for examples, oxalic acids, citric acid, acetic acid, etc.

Question 4.
A solution turns red litmus solution blue. Is the solution acidic or basic in nature?
Answer:
Basic.

Question 5.
Give two examples each of (i) Strong bases (ii) Weak bases.
Answer:
(i) Strong bases: Sodium hydroxide, potassium hydroxide.
(ii) Weak bases: Copper hydroxide, zinc hydroxide. .

Question 6.
What do you understand by the term “neutral substance?”
Answer:
The substances which do not bring about any change in the colour of common indicators are called neutral substances.

Question 7.
Name the acids present in:
(i) Vinegar
(ii) Lemon juice
Answer:
(i) Acetic acid (CH₃COOH)
(ii) Citric acid.

Question 8.
Write the names of three mineral acids.
Answer:
(i) Sulphuric acid (H₂SO₄)
(ii) Nitric acid (HNO₃) and
(iii)Hydrochloric acid (HCl) are mineral acids.

Question 9.
Which of the following are oxides?
H₂O, CO, Co, NO, CO₂ , NaOH
Answer:
Oxides: H₂O, CO, NO and CO₂.

Question 10.
From the following list select metallic oxide and non-metallic oxides: CaO, Fe₂O₃, N₂O₅, CO₂, Na₂O, SO₂.
Answer:
(i) Metallic oxide: CaO, Fe₂O₃ and Na₂O.
(ii) Non-metallic oxide: N₂O₅, CO₂ and SO₂.

Question 11.
What are indicators?
Answer:
The complex, naturally occurring substances, which change their colour on coming in contact with other substances are called indicators. Turmeric, litmus, china rose etc. are some indicators.

Question 12.
Name two neutral liquids.
Answer:
(i) Alcohol
(ii) Ether.

Question 13.
Name two neutral gases.
Answer:
(i) Hydrogen, (ii) Oxygen.

Question 14.
Name two neutral solids.
Answer:
(i) Common Salt
(ii) Sugar.

Question 15.
What do you understand by term concentrated acid?
Answer:
The acids which contain very little or no amount of water are called concentrated acids.

Question 16.
What are dilute acids?
Answer:
The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.

Question 17.
Name the kind of substance formed when an acid reacts with a base.
Answer:
Neutralised.

Question 18.
What is missing in the following equation?
Fat + ……. → Soap + Glycerol
Answer:
Fat + NaOH → Soap + Glyceral
Thus NaOH missing from the equation.

Question 19.
An element combines with oxygen to form an oxide. This oxide dissolves in water. This aqueous solution changes blue litmus to red. Write:
(i) The nature of element (metal or non-metal)
(ii) The general name of the oxide.
Answer:
(i) The element is non-metal.
(ii) General name of the oxide non-metallic oxide.

Question 20.
What happens when a non-metal oxide is dissolved in water?
Answer:
When a non-metal oxide is dissolved in water, it forms acids. Examples:
(i) CO₂ + HO₂ → H₂CO₃ (Carbonic acid).
(ii) SO₂ + HO₂ → H₂SO₃(Sulphuric acid).

Question 21.
State one characteristics, property of all acids.
Answer:
All acids contain replaceable hydrogen.

Question 22.
Name the gas obtained when a metal carbonate reacts with an acid.
Answer:
When a metal carbonate reacts with an acid, carbon dioxide gas is envolved. Example:

Question 23.
Write equations for the action of water on:
(i) MgO
(ii) Calcium oxide.
Answer:
(i) MgO + H₂O → Mg(OH)₂ (Magnesium hydroxide)
(ii) CaO + H₂O → Ca(OH)₂(Calcium hydroxide)

Question 24.
What are mineral acids? Give two examples.
Answer:
Mineral acids are those acids which are obtained from the earth. Examples, Sulphuric acid, Nitric acid.

Question 25.
Name the three salts which are commonly lised at home..
Answer:
Three, salts commonly used at home are:
(i) Sodium chloride
(ii)Sodium carbonate
(iii) Sodium hydrogen carbonate.

Question 26.
Give the chemical formula of slaked lime
Answer:
Chemical formula of slaked lime is Ca(OH)₂

Question 27.
Name one/compound of calcium which is used for bleaching cloth.
Answer:
Bleaching powder.

Question 28.
What is the formula of sulphuric acid?
Answer:
The formula of sulphuric acid is H₂SO₄.

Question 29.
A solution turns red litmus paper blue. What does this indicate about the chemical nature of the solution?
Answer:
The chemical nature of the solution is acidic.

Question 30.
What do you understand by anhydrous salt?
Answer:
Hydrated salts loose their water of crystallisation upon heating. They love their shape and colour also and becomes powered. They are called anhydrous salts.

Question 31.
Name two normal salts.
Answer:
(i) Sodium Chloride (NaCl)
(ii) Potassium nitrate (KNO₃).

Question 32.
Name two basic sdlts.
Answer:
(i) Calcium hydrdgen chloride [Ca(OH)Cl]
(ii) Magnesium hydroxy chloride [Mg(OH)Cl] etc.

Question 33.
Write the balanced chemical equations for the reaction that takes place when zinc, magnesium and sodium react with dilute hydrochloric acid.
Answer:
Reaction of hydrochloric acid (dil.) with Zn, Mg, and Na:
(i) Zn + 2HCl → ZnCl₂ + H₂
(ii) Mg + 2HCl → MgCl₂ + H₂
(iii) 2Na + 2HCl → 2NaCl + H₂

Question 34.
Write two uses of slaked lime.
Answer:
Uses of slaked lime:
(i) It is used in manufacture of bleaching powder.
(ii) It is used as an important building materials

Question 35.
Complete the following equations:
(i) CO₂ + H₂O → ……………..
(ii) CO₂ + 2Na0H → …………….. + ……………..
(iii) SO₂ + H₂O → ……………..
(iv) MgO + H₂SO₄ → …………….. + ……………..
(v) CaC0₃ + 2HCl → …………….. + ……………..
(vi) Na₂O + H₂O → ……………..
(vii) 2NaOH + H₂SO₄ → …………….. + ……………..
(viii) NaOH + HNO₃ → …………….. + ……………..
(ix) CaO + H₂SO₄ → …………….. + ……………..
(x) MgO + 2HCl → ……………..
Answer:
(i) CO₂ + H₂O → H₂CO₃ (carbonic acid)
(ii) CO₂ + 2Na0H → Na₂CO₃ + H₂O (sodium carbonate)
(iii) SO₂ + H₂O → H₂SO₃ (suiphurous acid)
(iv) MgO + H₂SO₄ → MgSO₄ + H₂O (magnesium sulphate)
(v) CaC0₃ + 2HCl → CaCl₂ + H₂O + CO₂ (Calcium Chloride)
(vi) Na₂O + H₂O → 2Na0H (sodium hydroxide)
(vii) 2NaOH + H₂SO₄ → Na₂SO₄ + H₂O (sodium suphate)
(viii) NaOH + HNO₃ → NaNO₃ + H₂O (sodiùm nitrate)
(ix) CaO + H₂SO₄ → CaSO₄ + H₂O (calcium sulphate)
(x) MgO + 2HCl → MgCl₂ +H₂O

Short Answer Type Questions

Question 1.
How can you test the presence of an acid in any substance?
Answer:
Acid can be tested in any substance by the following methods:
(i) Take a drop of the dilute solution of the substance on the tips of your tongue. If tastes sour, it is acidic.
(ii) Dip a blue litmus paper in the solution. If ‘ the colour of the litmus paper turns red, the solution is acidic.

Question 2.
What are organic acids? Give two examples.
Answer:
Soured milk, Lemon, Green mangoes and Karvanda are sour testing. All of them contain some naturally occuring acids. Such acids are also found in humans and plants materials. They are known as organic acids. The acids such as lactic acid, citric acid, tartaric acid and acetic acid are naturally occuring and known as organic acid.

Question 3.
What are the uses of mineral acids in industry?
Answer:
Use of’mineral acids in industry:
(i) Concentration sulphuric acid, nitric acid and hydrochloric acid are used in a large number of metallurgical operations, manufacture of fertilizers and preparations of large number of industrial chemicals.
(ii) Hydrochloric acid is used for removing the deposits from inside the boilers. This process is known as de-scaling.

Question 4.
What are indicators? Name two acid-base indicators.
Answer:
The substances which are used to identify whether a substance is an acid or base is called indicators. For example, litmus solutions give red colour with acids and blue colour with bases. Therefore, litmus is used as indicators. Substances which give different colours with acid and base are called acid-base indicators, for examples. Methyl orange, phenolphthalein.

Question 5.
What are acid salts? Give two examples.
Answer:
The salts which dissolves water to produce a solution, which behaves like an acid is called an acid salt.
Examples: Sodium hydrogen carbonate (NaHCO₃), Potassium hydorgen carbonate (KHCO₃), Sodium hydrogen sulphate etc.

Question 6.
How is potash alum prepared?
Answer:
A mixture of potassium sulphate and aluminium sulphate is dissolved in water and then the solution is concentrated. Potash alum is formed. It separates out as crystals.

Question 7.
Why are sodium bicarbonate and lemon juice used during indigestion?
Answer:
Sodium bicarbonate neutralizes the acidity in the stomach. Hence, it is used during indigestion. Lemon contains acid. It reacts with undigested food and softens it. Thus, lemon is also used in indigestion.

Question 8.
Why are brass vessels coated with tin or kalai?
Answer:
When brass vessels are used to cook food with tamarind or lemon juice, the acids present in it reacts with brass metal and corrode it. The kalai layer protects this vessels from the action of acids. Due to this reason brass vessels are coated with tin.

Question 9.
What is salt? Name any salts and give thier formulae.
Answer:
A substance formed by the neutralisation of an acid with a base is called salt.
Examples:
(i) Potassium nitrate (KNO₃)
(ii) Sodiun: nitrate (NaNO₃)
(iii) Calcium carbonate (CaCO₃)
(iv) Zinc sulphate (ZnSO₄)
(v) Copper sulphate (CuSO₄).

Question 10.
Define an acid. Give three properties of acids.
Answer:
An acid is a substance which when dissolved in water gives hydrogen ions. Examples: H₂SO₄, HNO₃ and HCl etc.
Properties of acids:
(i) They have a sour taste
(ii) They turn blue litmus solution red.
(iii) They have replaceable hydrogen ion.

Question 11.
What are bases? Mention three properties of alkalies.
Answer:
The substance which react with acids to form salt and water only are called bases. Examples: Cu(OH)₂, Fe(OH)₃, Pb(OH)₂ etc.
Properties of alkalies:
(i) They tarn red litmus paper blue
(ii) They have a better taste.
(iii) They turn methyl orange from pink to yellow.

Question 12.
What are the uses of sodium bicarbonate?
Answer:
Uses of sodium bicarbonate:
(i) It is used in medicines to neutralise the acidity in the stomach.
(ii) It is used as backing power.
(iii) It is used in fire extinguisher.

Question 13.
What are the uses of common salt?
Answer:
Uses of common salt:
(i) It is an essential constituents of our diet.
(ii) It is used in the manufacture of soap.
(iii) It is used for glazing pottery. .
(iv) It is a starting material for the manufacture of chlorine, hydrochloric acid, washing soda and sodium hydroxide.
(v) It is used as food preservatives.
(vi) It turns freezing mixture with ice.

Question 14.
Give five uses of potassium nitrate.
Answer:
Uses of potassium nitrate:
(i) It is used in the manufacture of gun powder.
(ii) It is used in making fire works.
(iii) It is used in refrigeration.
(iv) It is used as fertilizers.
(v) It is used in glass industry.

Question 15.
Which acids is called ‘the king of the acids’? Give its uses.
Answer:
Sulphuric acid (H₂SO₄) is called “the king of the acids”.
Uses of sulphuric acid:
(i) It is used in the manufacture of detergents.
(ii) It is used as a dehydrating agent.
(iii) It is used in storage batteries.
(iv) It is used in petrol refining.
(v) It is used in textile, paper and leather industry.
(vi) It is used in fertilizers industry for the manufacture of ammonium sulphate and superphosphate of lime.

Question 16.
Explain with the help of chemical equations how the following acids are formed?
Carbonic acids, Sulphurous acid, Phosphoric acid.
Answer:
(i) Carbonic acid is prepared by dissolving carbon dioxide in water.
CO₂ + H₂O → H₂CO₃ (Carbonic acid)

(ii) Sulphurous acid is formed by dissolving sulphur dioxide in water.
SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

(iii) Phosphoric acid is prepared by dissolving phosphorus pentaoxide in hot water.
P₂O₅ + 3H20 → 2H₃PO₄ (Phosphoric acid)

Acids, Bases and Salts Class 7 HBSE Notes

1. Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids. The chemical nature of such substances is acidic. The word acid comes from the Latin word acere which means sour. The acids in these substances are natural acids.
2. A substance which produces hydrogen (H⁺) ions when dissolved in water is called an acid. This definition was given by Arrhenius, a Swedish Chemist in 1912.
3. The acids which are prepared from the minerals of the Earth are called mineral acids.
Examples of Mineral Acids

Name of Acid	Formula
Sulphuric acid	H2SO4
Nitric acid	HNO4
Hydrochloric acid	HCl
Phosphoric acid	H3PO4

4. The acids which dissolve in water to give a large number of positively charged hydrogen ions are called strong acids.
Examples of Strong Acids : Sulphuric acid, nitric acid, hydrochloric acid and phosphoric acid are examples of strong acids.
5. The acids which dissolve in water to give a small number of positively charged hydrogen ions are called weak acids.
Examples of Weak Acids : Carbonic acid, acetic acid, sulphurous acid, formic acid, etc., are examples of weak acids. In fact, most of the organic acid are weak acids.
6. The acids which contain very little or no amount of water are called concentrated acids.
7. The acids which contain a large amount of water (or solutions of acids in water) are called dilute acids.
8. General Physical Properties of Acids
(i) They have a sour taste.
(ii) They turn blue litmus solution red.
(iii) They turn methyl orange solution pink.
(iv) They do not affect phenolphthalein solution.
(v) Strong acids have a corrosive action on skin. They cause painful blisters.
(vi) Most of the acids are soluble in water.
(vii) Acids solutions are conductors of electricity.
9. Uses of Acids

Acids	Uses
(i) Sulphuric acid	• manufacturing fertilizers, drugs, detergents, paints, plastic and artificial silk. • in strong batteries. • in paper, textile and leather industries. • as dehydrating agent.
(ii) Hydrochloric acid	• purifying metals and common selt. • making glucose, glue • bleaching textiles
(iii) Nitric acid	• extracting metals from ores brass, etc. • making designs on copper, • manufacturing explosives, fertilizers, perfumes, medicines and plastic.
(iv) Citric acid	• in food preservation • preparing effervescent salts.

10. The substances which react with acids to form salt and water as only products are called bases. All oxides of metals are bases. All hydroxides of metals are bases.
11. All bases which are soluble in water are called alkalis.
12. Strong bases completely dissociate in aqueous solution. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), etc.
13. They undergo partial dissociation in aqueous solution. For example, copper hydroxide Cu(OH)₂, Zinc hydroxide Zn(OH)₂, etc.
14. The bases show the following properties:
(i) These have a bitter taste.
(ii) Bases neither have colour nor small. Only Ammonium hydroxide (NH₄OH) has a pungent smell.
(iii) The basic solutions are soapy to touch, i.e., if little amount of sodium hydroxide is rubbed on fingers, it would give a feeling as if soap has been applied on the fingers.
(iv) Bases turn red litmus blue.
(v) Bases contain hydroxide ions e.g., Sodium hydroxide is represented as NaOH, calcium hydroxide is represented as Ca(OH)₂, etc., where OH is the hydroxy group.
(vi) Bases react with acids to give salt and water.
15. Uses of Bases

Bases	Uses
(i) Calcium Hydroxide (slaked lime)	• manufacturing of bleaching powder, fungicides, plasters, etc. • neutralising soil acidity. • water softening agent. • antidote for acid poisoning.
(ii) Ammonium Hydroxide	• removing grease from • clothes and from window panes. • reagent in laboratory.
(iii) Magnesium Hdroxide	• antacid to neutralize stomach acidity.

16. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. Turmeric, litmus, china, rose, petals (Gudhal), etc., are some of the naturally occurring indicators.
17. The reaction between an acid and a’base-is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water (Heat is evolved)
The following reaction is an example :
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

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Haryana State Board HBSE 7th Class Science Solutions Chapter 9 Soil Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 9 Soil

HBSE 7th Class Science Soil Textbook Questions and Answers

Tick the most suitable answer in questions 1 and 2.

Question 1.
In addition to the rock particles, the soil contains:
(i) air and water,
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants.
Answer:
(iii) minerals, organic matter, air and water.

Question 2.
The water holding capacity is the highest in:
(i) sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam
Answer:
(iii) loamy soil.

Question 3.
Match the items in column I with those in column II:

Column I	Column II
(i) A home for living organisms	(a) Large particles
(ii) Upper layer of the soil	(b) All kinds of soil
(iii) Sandy soil	(c) Dark in colour
(iv) Middle layer of the soil	(d) Small particles and packed tight
(v) Clayey soil	(e) Lesser amount of humus

Answer:

Column I	Column II
(i) A home for living organisms	(b) All kinds of soil
(ii) Upper layer of the soil	(c) Dark in colour
(iii) Sandy soil	(a) Large particles
(iv) Middle layer of the soil	(e) Lesser amount of humus
(v) Clayey soil	(d) Small particles and packed tight

Question 4.
Explain how soil is formed.
Answer:
Soil has been formed from parent rock material over millions of years. The process by which soil formation takes place is called weathering. Weathering is a very slow and gradual process during which parent rock material breaks down into fine particles.

The agents which bring about weathering are many. These are described below:
1. Temperature changes:
Rocks expand when heated and contract when cooled. The hot sun causes the surface layers of rocks to expand more than the layers deeper down. These changes cause the rock surface to break apart.

2. Frost:
Rainwater may become trapped in small crevices of the parent rock. In winter, this water freezes to ice. The ice expands producing a lateral pressure, causing the crevices in the rocks to further open up.

3. Water:
Continual movement of rain and river water, in liquid form, causes breaking down of rock particles into finer particles through their abrasive effect.

4. Wind:
Wind blowing across a rock surface also has a abrasive effect on the rocks. Minute rock particles are carried away by the blowing wind and deposited elsewhere.

Question 5.
How is clayey soil useful for crops?
Answer:
Clayey soils are very useful for crops, because these soils:
(i) contain humus, providing fertility to the soil
(ii) hold sufficient water due to the presence of smaller particles, and
(iii) contain enough air due to the presence of some large particles alsy.

Question 6.
List the differences between clayey soil and sandy soil.
Answer:
Clayey soil:
Clayey soil contains more than 50% of clay particles. Since the clay particles are very small in size, they are very tightly packed and do not allow water to drain out easily. It is poorly aerated because the tightly bound clay particles leave little space in between to trap air. Clayey soil is very sticky and thus tilling the soil is very difficult. However, it is rich in minerals which makes it suitable for plant growth. Due to the great binding capacity of its particles, clayey soil is used for making toys and pots.

Sandy soil:
Sandy soil contains about 60% of sand particles with small amounts of silt and clay. It is very porous and its water holding capacity is very low as all the water easily runs down through the large pores. This type of soil is, therefore, not good for the growth of plants. It is found mainly in the deserts.

Question 7.
Sketch the cross section of soil and label the various layers.
Answer:
Soil profile

Question 8.
Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Answer:
Formula: Percolation rate
\((\mathrm{mL} / \mathrm{min})=\frac{\text { amount of water }}{\text { percolation time }(\mathrm{min})}\)
= \(\frac{200 \mathrm{~mL}}{40 \mathrm{~min}}\)
= 5 mL /min.

Question 9.
Explain how soil erosion could be prevented.
Answer:
Prevention of soil erosion can be brought about by controlling the factors which cause soil erosion. The methods would, thus, be as follows:
1. Deforestation should be stopped. Rather, trees should be planted (afforestation). Afforestation should be undertaken not only in areas already cut, but additional areas should be brought under plantation.

2. To reduce the effect of strong winds in the fields, the boundaries of the fields should be planted with trees in two to three rows.

3. To maintain the soil in its natural condition, it is advisable to grow different crops. Crops rotation, as it is called, helps to maintain the fertility of the soil. The water-holding capacity of the soil is also maintained by this method.

4. Proper drainage and irrigation arrangements should be made in the fields.

5. On the sloping areas in hills, strip cropping should be practised, thereby reducing the steepness of the slopes and checking soil erosion.

Question 10.
Solve the following crossword puzzle with the clues given:

Across:
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.

Down:
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Answer:

Extended Learning – Activities And Projects

Question 1.
Boojho would like to know the difference between raw and baked soil? Investigate how the soil from which matkas are made is different from the soil used to make status.
Answer:
Do yourself. Take help your teacher.

Question 2.
Paheli is worried. She could see a brick kiln from her house. Bricks were being made there. There was so much smoke coming out of the kiln. She was told that the best quality of clay is required for making pottery, statues and bricks. She has seen truck loads of bricks being taken away for construction of buildings. At this rate, she fears, no soil will be left. Are her fears justified? Discuss this problem with your parents, teachers and other experts of your area and prepare a report.
Answer:
Do yourself.

Question 3.
Try to find out the moisture content of a soil sample. One method is given here.
Activity: Take lOOg soil. (Take help from any shopkeepers to weigh the soil). Place it on a newspaper in the sun and allow it to dry for two hours. This activity is best done in the afternoon. Take care that the soil does not spill outside the newspaper. After drying it, weigh the soil again. The difference in the weight of the soil before and after drying gives you the amount of moisture contained in 100 g of soil. This is called the percentage moisture content.
Suppose your sample of soil loses 10 g on drying. Then
Percent of moisture in soil
= \(\frac{\text { wt. of moisture }(\mathrm{g})}{\text { Original wt. of soil sample }(\mathrm{g})} \times 100\)
In this example
Percent of moisture in soil
= \(\frac{10 \times 100}{100}=10 \%\)
Answer:
Do yourself.

HBSE 7th Class Science Soil Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define soil.
Answer:
Soil is uppermost layer of earth’s crust, in which plants grow.

Question 2.
Define weathering.
Answer:
Soil is formed from the parent rock material by a very slow and gradual process called weathering.

Question 3.
What is humus?
Answer:The rotting dead matter in the soil is called humus.

Question 4.
Where do plants grow?
Answer:
Plants grow in the soil.

Question 5.
Where does food that helps to sustain and grow, come from?
Answer:
Plants.

Question 6.
How old is our earth?
Answer:
Our earth came into existence about 4.5 billion years ago.

Question 7.
Name the part of the environment which supports life.
Answer:
1. Lithosphire
2. Hydrosphere
3. Atmosphere.

Question 8.
Give one term for the following,
“Removal of top soil by air and water.”
Answer:
Soil erosion,

Question 9.
What do you understand by the term soil conservation?
Answer:
Prevention of soil erosion is called soil conservation.

Question 10.
What is soil pollution?
Answer:
When the structure and properties of the soil are changed by adding unwanted and harmful substances, it is called as soil pollution.

Question 11.
Name two soil pollutions.
Answer:
(i) Insecticides and herbicides
(ii) Industrial wastes like plastic, chemicals, flyash, leather etc.

Question 12.
How soil erosion takes place?
Answer:
When the over grazing or cutting of trees take place the top soil becomes soft and loose which is easily blown by wind and water.

Question 13.
How is soil formed?
Answer:
Soil is formed by cracking of rocks due to contraction and expansion by cooling and heating effect.

Question 14.
What is mineral?
Answer:
Minerals are the non-renewable natural resources.

Question 15.
Name four animals that live in the soil.
Answer:
Bacteria, Earthworm, Snakes, Rats, Ants.

Question 16.
What do you understand by deforestation?
Answer:
When the trees of the forest are cleared to convert the forest land into formland is called deforestation.

Question 17.
State two major problems caused by excessive deforestation.
Answer:
(i) Due to excessive deforestation there is less rain.
(ii) Soil erosion takes place.

Question 18.
Name the materials present in fertile soil.
Answer:
Fertile soil contains nitrates, phosphates, water soluble salts and carbonic acids.

Question 19.
What is crumb?
Answer:
The main skeleton of a fertile soil is called crumb.

Question 20.
What, is the function of air in soil?
Answer:
(i) Air helps, 1:he plants present in the soil in respiration.
(ii) It helps in making soil soft and light in weight.

Question 21.
Which soil horizon is rich in humus?
Answer:
The uppermost layer is called the A- horizon is rich in humus.

Question 22.
Which type of soil is best suited for growth of plants?
Answer:
Loamy soil.

Question 23.
Name the different types of particles present in soil.
Answer:
Soil consists of soil particles, humus (organic matter), water, air and living organisms.

Question 24.
What is strip, cropping?
Answer:
Strip cropping means the planting of crops in rows or strips to check flow of water.

Question 25.
What are loams?
Answer:
Soils having mixtures of different sized particles are called loams or loam soils.

Short Answer Type Questions

Question 1.
What are the components of soil?
Answer:
Some of the main components of soil are as follows:
(i) Humus
(ii) Minerals
(iii) Water
(iv) Air and
(v) Micro organisms 7 bacteria, fungi, insects, larvae and many other organisms.

Question 2.
Write the importance of Humus.
Answer:
Humus is very important for the proper growth of the plants. It helps in growing plants in the following ways:
(i) It makes the soil fertile.
(ii) It allows the roots of plants to penetrate in the soil easily.
(iii) Water and air can pass into it easily,
(iv) It retains water for a longer period.
(v) It binds the soil particles.

Question 3.
What is meant by term wehtherifig?
Answer:
The cooling and heating of rocks cause cracking. They bring about further breaking. This process of breaking the parent rock into fine particles is called weathering.

Question 4.
Describe the harmful effects of deforestation.
Answer:
Deforestation causes the following harmful effects:
(i) Soil erosion will take place.
(ii) There will be draught due to which famine will occur. .
(iii) There will be less rain.
(iv) There will be excess amount of CO, due to which Green House effect will take place. It may cause flood in-the rivers.

Question 5.
Why biosphere supports life?
Answer:
Biosphere has all those requirements such as air, water, minerals, sunlight etc. which are essential for the survival of living things.

Question 6.
What are natural resources?
Answer:
Natural resources are those which are provided by nature to support life. Such as water, air, minerals, sunlight and various life forms.

Question 7.
What is soil erosion?
Answer:
The top soil being soft and light is carried away easily by wind and water, the natural agents. This process of removal of soil is called soil erosion.

Question 8.
Distinguish between residual and transported soils.
Answer:
Residual soils are those in which the whole process of soil formation, i.e., weathering and development of soil profile occurs at the same place. In these soils, the soil is formed at the place where the parent rock is present.

Transported soils are those where the v weathered soil particles are taken away to other places. This is done by several agents.

Question 9.
State any four major advantages of forests.
Answer:
Forest is a natural renewable resource which is advantageous in the following ways:
(i) It creates a suitable environment for rain.
(ii) It helps in controlling the soil erosion.
(iii) It absorbs excess rain water as subsoil water.
(iv) It provides the home to variety of animals.

Question 10.
What is the importance of soil organisms?
Answer:
A number of organisms such as earthworms, bacteria, fungi and round- worms are found in the soil.
Soil organisms are important because of various uses:
1. As you know, earthworms burrow the soil, swallow it and make it loose and soft.
2. Micro-organisms cause the decomposition’ of dead plants and animals, and release the minerals back of the soil. The minerals can again be absorbed by the plant roots. Mineral cycling goes on in this manner.
3. Some bacteria are able to fix nitrogen in association with roots of legume plants like pea and gram.

Long Answer Type Questions

Question 1.
How is soil important to us? Explain.
Answer:
Our mother Earth is blessed with immense land resource. It is valuable to man for food production. It is also a basic part of wildlife habitats and recreational resources. Various soil organisms like earthworms, bacteria, insects and mammals use this as a natural habitat. Plants obtain water and minerals through this land resource. Plant sources of many medicinal drugs exist here. Wood fibres, fruits, rubber, oils, dyes and various other economic products which the man uses, are all dependent on this land. The very existence of mankind is greatly influenced by this land resource.

Question 2.
Describe the factors which cause soil erosion.
Answer:
Soil erosion is the removal of topsoil. This is brought about by wind and water or rain. There are several factors which allow water and wind to cause soil erosion. Some of these factors are:
(i) Deforestation:
Cutting down of trees and excessive farming are practices that destroy vegetation and expose land to the action of wind and water. Water runs off the soil surface with great speed and carries the soil particles into rivers which get chocked with silt resulting in floods. This problem assumes alarming proportions on hills.

(ii) Overgrazing:
Overgrazing by animals also destroys vegetation making land barren. The top soil on barren land can then be eroded by water and wind.

(iii) Poor methods of farming:
Tilling or ploughing loosens the soil which can then be easily eroded by wind and water. Due to excessive farming the layer of humus gets depleted and water holding capacity of the soil also reduces. The topsoil thus dries up and can be carried away by wind and water.

(iv) Forest fires, too, lead to soil erosion. After fire, the soil is exposed to two main factors causing erosion, namely wind and water.

Question 3.
Write short notes on the importance of the following:
(а) Soil, (b) Forests, (c) Soil organisms, (d) Overgrazing, (e) Earthworms.
Answer:
(a) Soil:
(i) Soil provides shelter to several micro-organism and some macro- organisms.
(ii) All the plants grow in it.
(iii) It acts as store-house of minerals.
(iv) It acts as raw material for building bricks, mortar, pottery, pulp for paper industry is. obtained from plants grown in the soil.
(v) It acts as water storage.
(vi) It provides employment.

(b) Forests: Forests are very useful to man-kind in the following ways:
(i) It maintains the balance of gases in the atmosphere.
(ii) It causes rain.
(iii) It provides the shelter to the wild animals.
(iv) It provides the valuable things like timber, honey, bee wax, lac, medicines.

(c) Soil Organisms:
Various micro organisms live in the soil which make the soil porous, soft and airy. They make soil fertile. They convfert manure into simple form which can be used by plants of the forest.

(d) Overgrazing:
When the cattle , eat grass of l^rge area, it is called as overgrazing. This process makes the soil plain which can be used for industrialisation and urbanisation.

(e) Earthworm:
Earthworms are the friends of the farmer. They eat dead organicv substances along with the soil and convert them into simple soluble forms which make the soil fertile and soft.

Question 4.
Describe the composition of soil.
Answer:
Composition of soil varies from place to place. It depends on the type of rock from which it is formed. However, all soils contain the following components:
(i) Rock particles: Tiny particles of soil derived from the parent rock.
(ii) Humus: Humus consists of decaying remains of plants and animals.
(iii) Living organisms: Soil contains a large number of micro-organisms like bacteria, algae, fungi and protozoa. Many small animals like insects, earthworms, spiders, scorpions, centipedes and millipedes are found in the soil. Burrowing animals like rats, moles, rabbits and guinea pigs make tunnels in the soil.
(iv) Water: Water is present in pores between soil particles and helps the plants in their growth.
(v) Air: Air is also present in the soil pores and is essential for the survival of living organisms present in the soil.

Question 5.
What is soil pollution? What are the major sources of soil pollution?
Answer:
Any substance that adversely affects the, productivity of soil is called a soil pollutant. Contamination of soil with pollutants like insecticides, artificial fertilizers and industrial wastes is called soil pollution. The major sources of soil pollution are:
(i) Pollutants like acids washed off from the atmosphere (acid rain).
(ii) Pesticides and herbicides sprayed in fields.
(iii) Excessive use of artificial fertilizers.
(iv) Solid wastes like garbage, trash, ash, building material, plastic bottles and cans.

Soil Class 7 HBSE Notes

1. Soil is the uppermost layer of earth’s crust, in which plants grow.
2. Soil is formed from the parent rock material by a very slow and gradual process called weathering. A number of agents temperature changes, frost, water, wind and living organisms – are involved in the weathering of rocks.
3. Six types of soil are mainly found in India – Red soil, black soil, alluvial soil, desert soil, mountain soil and laterite soil. Humus content is maximum in mountain soil. Black soils are rich for growing cotton and sugarcane while alluvial soil is suitable for wheat and rice.

Types of soil	Occurrence	Characteristics
1. Red soil	Interior regions of Kerala and .Tamil Nadu, Southern Karnataka, Andhra Pradesh, Orissa, Eastern Madhya Pradesh.	(i) Red colour due to the presence of iron oxide. (ii) Poor in humus but can be made fertile by adding manure or fertilizers.
2. Black soil	Maharashtra, parts of Andhra Pradesh, Madhya Pradesh and Gujarat.	(i) Rich in iron and magnesium, derived from basaltic rocks. (ii)Soil is clayey, contains dead organic matter and water ideal for growing cotton and sugarcane.
3. Alluvial soil	Plains of Haryana, Punjab, Uttar Pradesh, Bihar, West Bengal, Coastal Orissa and Andhra Pradesh.	(i) Loamy in texture with plenty of humus. (ii)Very fertile; good for crops like wheat and rice.
4. Desert soil	Rajasthan and some parts of Gujarat.	(i) Soil sandy and porous, cannot hold much water. (ii) If irrigated, crops can be grown.
5. Mountain soil	Himalayan region and north-east India.	Of all the soil types, humus content is maximum in this type and, thus, it is very fertile.
6. Laterite soil	Found in regions with heavy rains; parts of Tamil Nadu, Andhra Pradesh, Orissa and Assam.	(i) Soil rich in nutrients. (ii) Good for plantation of tea, coffee and coconut.

4. There are three main layers or horizons in the soil profile – A-horizon (top soil), B horizon (subsoil) and C-horizon (parent rock).
5. Soil consists of soil particles, humus (organic matter), water, air and living organisms.
6. Soil particles, depending on size, consist of clay (below 0.002 mm), silt (0.002 to 0.02 mm), sand (0.02 to 2.0 mm) and gravel (above 2.0 mm).
7. A soil containing a mixture of sand, silt and clay is called a loamy soil. It is the best soil for plant growth.
8. Soil is an important natural resource. It provides us food, clothing, shelter, medicines,
rubber, dyes and a number of other useful products. Besides man, it provides shelter to wildlife and different soil organisms.
9. Wind and rain bring about loss of the top soil (soil erosion). Deforestation, over grazing and poor farming methods have accelerated the process of soil erosion.
10. Prevention of soil erosion (soil conservation) can be brought about by growing plants (afforestation), crop rotation, prevention of over grazing maintaining proper drainage, and growing of crops in rows or strips in the hills (strip-cropping).

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Haryana State Board HBSE 7th Class Science Solutions Chapter 13 Motion and Time Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 13 Motion and Time

HBSE 7th Class Science Motion and Time Textbook Questions and Answers

Question 1.
Classify the following as motion along a straight line, circular or oscillatory motion :
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry go round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bed.
(vi) Motion of a train on a straight bridge.
Answer:
(i) Oscillatory
(ii) along a straight, line
(iii) circular
(iv) oscillatory
(v) oscillatory
(vi) along a straight line.

Question 2.
Which of the following is not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distance between two cities are measured in kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.
Answer:
(ii), (iv) (v).

Question 3.
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer:
Time period of a pendulum is time taken to complete 1 oscillation
Time taken to complete = 32 s.
20 oscillations
Time taken to complete = \(\frac { 32 }{ 20 }\)s.
1 oscillation
= 1.6 s.
∴ Time period of pendulum is 1.6 seconds.

Question 4.
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer:
Distance = 240 km.
Time taken = 4 hr.
Speed = \(\frac { Distance covered }{time taken }\)
= \(\frac { 240 }{ 4 }\) \(\frac { km }{ h }\)
= 60 km/h.
Speed of the train is 60 km/h.

Question 5.
The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/ h also.
Answer:
Distance = 57336.0 km – 57321 km = 15 Km
Time = 8.50 Am. – 8.30 Aim. = 20 min
Speed = \(\frac { Distance }{ time }\) = \(\frac { 15 }{ 20 }\) km/m
= 0.75 km/m. = 45 km/h

Question 6.
Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s. Calculate the distance between her house and’the school.
Answer:
Time taken = 15 min
Speed = 2 m/s.
Distance = Speed x time
= 15 x 2
= 30 m.
So, distance between Salma’s School and her house is 30 metre.

Question 7.
Show the shape of the distance-time graph for the motion in the following cases :
(i) A car moving with a constant speed.
(ii) A car parked on a side road.
Answer:

Question 8.
Which of the following relations is correct?
(i) Speed = Distance x Time
(ii) Speed = \(\frac { Distance }{ Time }\)
(iii) Speed = \(\frac { Time }{ Distance }\)
(iv) Speed = \(\frac { 1 }{ Distance x Time }\)
Answer:
(ii) Speed = \(\frac { Distance }{ Time }\) is correct.

Question 9.
The basic unit of speed is :
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s
Answer:
(iv) m/s

Question 10.
A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is :
(i) 100 km
(ii) 25 km
(iii) 15 km
(iv) 10 km
Answer:
(ii) 25 km

Question 11.
Suppose, the two photographs shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs. Calculate the speed of the blue car.
Answer:
0.1 cm/s or 10 m/s.

Question 12.
Fig. 13.16 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Answer:
‘A’ car is moving faster.

Question 13.
Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Answer:

Extend Learning – Activities and Projects

Question 1.
You can make your own sundial and use it to mark the time of the day at your place. First of all find the latitude of your city with the help of an atlas. Cut out a triangular piece of a cardboard such that its one angle is equal to the latitude of your place and the angle opposite to it is a right angle. Fix this piece, called gnomon, vertically along a diameter of a circular board a shown in Fig. 13.4. One way to fix the gnomon could be to make a groove along a diameter on the circular board.

Next, select an open space, which receives sunlight for most of the day, Mark a line on the ground along the North-South direction. Place the sundial in the sun as shown in Fig. 13.4 Mark the position of the tip of the shadow of the gnomon on the circular board as early in the day as possible, say 8:00 AM. Mark the position of the tip of the shadow every hour throughout the day. Draw lines to connect each point marked by you with the centre of the base of the gnomon as shown in Fig. 13.4. Extend the lines on the circular board up to its periphery. You can use „ this sundial to read the time of the day at your place. Remember that the gnomon should always be placed in the North- South direction as shown in Fig. 13.4.

Answer:
Do it yourself.

Question 2.
Collect information about time-measuring devices that were used in the ancientitimes in different partrs of the world. Prepare a brief write up on each one of them. The write up may include the name of the device, the place of its origin, the period when it was used, the unit in which the time was measured by it and a drawing or a photograph of the device, if available.
Answer:
Do it yourself

Question 3.
Make a model of a sand clock which can measure a time interval of 2 minutes (Fig. 13.5).

Answer:
Do it yourself

Question 4.
You can perform an interesting activity when you visit a park to ride a swing. You will require a watch. Make the swing oscillate without anyone sitting on it. Find its time period in the same way as you did for the pendulum. Make sure that there are no jerks in the motion of the swing. Ask one of your friends to sit on the swing. Push it once and let it swing naturally. Again measure its time period. Repeat the activity with different persons sitting on the swing. Compare the time period of the swing measured in different cases. What conclusions do you draw from this activity?
Answer:
Do it yourself.

HBSE 7th Class Science Motion and Time Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is motion?
Answer:
Motion is the change in the position of a body with respect to time and its surroundings.

Question 2.
What is uniform motion?
Answer:
When a body covers equal distance in equal intervals of time, the motion is called uniform motion.

Question 3.
What is speed?
Answer:
Speed is the distance covered by a body in a unit time.

Question 4.
Write one way in which people used to measure time in early days?
Answer:
People used to measure time with the help of Sundials.

Question 5.
What is the use of stop-watch?
Answer:
Stop-watch is used to measure exact time in case of athletic events as it can be stopped and started any moment.

Question 6.
What is a pendulum?
Answer:
A pendulum is a small non-magnetic ball like body, suspended by a light string.

Question 7.
What is a uniform motion?
Answer:
Motion of a body along a straight line covering equal distances in equal intervals of time is called a uniform motion.

Question 8.
What are the units of measuring speed?
Answer:
Speed is measured in metre per second (m/s) or kilometre per hour (km/h).

Short Answer Type Questions

Question 1.
Distinguish between uniform and non-uniform motion.
Answer:
Uniform motion is the equal distances covered in equal intervals of time. It means body moves with a constant speed. Non-uniform motion is the unequal distances covered in equal intervals of time. It means the body moves with unconstant speed.

Question 2.
How can we make a pendulum of our own? What is the time period of a pendulum?
Answer:
We can make a pendulum by susptending a metal ball with a cotton thread. The other end of the thread can be tied to some support. The time taken by a pendulum to complete its to and fro movement i.e. one oscillation is called the time period of the pendulum.

Question 3.
How can we determine the motion made by any body to be uniform or non-uniform with the help of a distance – time graph?
Answer:
If the distance – time graph obtained shows a straight line, the motion of the body is said to be uniform and if we obtain a curved line on a distance time graph that means the body is undertaking non-uniform motion. Thus a distance time graph helps in determining the uniform or non-uniform speed of the body.

Question 4.
A train is running at a speed of 50 km/h. How long will it take to cover a distance of 250 km.?
Answer:
Speed = 50 km/h
Distance = 250 km.
Time = ?
S = \(\frac { d }{ t }\)
50 = \(\frac { 250 }{ t }\)
∴ t = \(\frac { 250 }{ 50 }\) hr = 5 hr.

Question 5.
Shatabdi Express takes 6 hours to reach Lucknow, at a speed of 60 km/h. Find the distance it travels.
Answer:
Time = 6 hr.
Speed = 60 km/h
Distance = Speed x time
= 60 x 6 = 360 km
∴ Shatabdi travels 360 km at a speed of 60 km/h in 6 hr.

Question 6.
A car travels a distance of 200 km at the speed of 50 km/h. Calculate the time taken to cover the distance.
Answer:
Distance = 200 km
Speed = 50 km/h
Time = \(\frac { Distance }{ Speed }\) = \(\frac { 200 }{ 50 }\) = 4h
Car will take 4 h to cover the distance.

Long Answer Type Questions

Question 1.
Given below is a table showing time taken by a car to travel various distances. What do you infer from this data?

Time (S)	Distance (M)
0	0
1	10
2	20
3	30
4	40
5	50

Answer:
We see that the car covers the distance of first 10 m in 1 sec. It again covers the distance of 10 m in another time of 1 sec i.e. 2-1 = 1 sec. So, we find that the car covers every 10 m in each 1 sec. It means that the car is covering equal distance in equal interval of time. When a body covers equal distance in equal intervals of time, it is said to be in a uniform motion. So, this data shows that the car is moving with a constant speed.

Question 2.
Describe various methods used to measure time in earlier times?
Answer:
There were no electronic watches in earlier times. Measuring time was a little bid difficult. The earliest method of measuring time was based on the position of the Sun. The Sundials were used for this purpose. Time was measured by the shadow casted by the changing position of the Sun from day to night. Chinese made a water clock 6000 years ago. Sand Clock was also used to measure time. Sand Clock was used by Romans. The time taken by sand to fall into the lower chamber from the upper chamber was considered to be the unit of measuring time. The discovery of pendulum helped in determining the exact time before the electronic watches were invented.

Question 3.
What is a pendulum? How does it help in determing time?
Answer:
Pendulum is a simple device which shows periodic motion. A simple pendulum consists of a non-magnetic metal ball called bob. This bob is suspended with help of a string. The open end of the string is tied to a support. Bob of the pendulum is held at a side and released. It starts moving in a to and fro motion. This is called an oscillatory motion. The time taken by the pendulum to complete one oscillation is called time period. This time period is always same with a pendulum having same length. Time period changes with the change in the length of the string. The string of the pendulum is adjusted to the length, that it completes one oscillation in second and it keeps on moving the clock giving us time.

Motion and Time Class 7 HBSE Notes

• Motion is the change in the position of an object with respect to its surroundings.
• Motion can be of many types. It can be along a straight line, circular, oscillatory.
• Motion can be uniform or non-uniform motion.
• Uniform motion means equal distance covered in equal intervals of time. It means a constant motion.
• Non-uniform motion means unequal distance covered in equal intervals of time.
• Distance moved by an object in unit time is called its speed.
• Basic unit of measuring speed is (m/s) meter / second.
• Time is measured in respect to the periodic motions.
• Pendulum was the first device to measure time exactly.
• In earlier days time Was measured by various objects like sundials, sand clocks, water clocks, etc.
• With the discovery of pendulum, devices to measure exact time were invented.
• Now-a-days various devices like stop-watch and other electronic devices are used to measure time intervals smaller than even a second.
• Distance time graph gives us the an idea about the motion of the object. Straight line obtained on this graph depicts constant motion, while non-constant motion is depicted by various shapes on the graph.

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Haryana State Board HBSE 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव Ex 2.4 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 2 भिन्न एवं दशमलव Ex 2.4

प्रश्न 1.
ज्ञात कीजिए :
(i) 12 ÷ \(\frac {3}{4}\)
(ii) 14 ÷ \(\frac {5}{6}\)
(iii) 8 ÷ \(\frac {7}{3}\)
(iv) 4 ÷ \(\frac {8}{3}\)
(v) 3 ÷ 2\(\frac {7}{3}\)
(vi) 5 ÷ 3\(\frac {4}{7}\)
हल :

प्रश्न 2.
निम्नलिखित भिन्नों में से प्रत्येक का व्युत्क्रम ज्ञात कीजिए। व्युत्क्रमों को उचित भिन्न, विषम भिन्न एवं पूर्ण संख्या के रूप में वर्गीकृत कीजिए:
(i) \(\frac {3}{7}\)
(ii) \(\frac {5}{8}\)
(iii) \(\frac {9}{7}\)
(iv) \(\frac {6}{5}\)
(v) \(\frac {12}{7}\)
(vi) \(\frac {1}{8}\)
(vii) \(\frac {1}{11}\)
हल :
(i) \(\frac {3}{7}\) का व्युत्क्रम = \(\frac {7}{3}\) है, यह उचित भिन्न नहीं है।
(ii) \(\frac {5}{8}\) का व्युत्क्रम = \(\frac {8}{5}\), यह उचित भिन्न नहीं है।
(iii) \(\frac {9}{7}\) का व्युत्क्रम = \(\frac {7}{9}\), यह उचित भिन्न है।
(iv) \(\frac {6}{5}\) का व्युत्क्रम = \(\frac {5}{6}\), यह उचित भिन्न है।
(v) \(\frac {12}{7}\) का व्युत्क्रम = \(\frac {7}{12}\), यह उचित भिन्न है।
(vi) \(\frac {1}{8}\) का व्युत्क्रम = \(\frac {8}{1}\) = 8, यह उचित भिन्न है।
(vii) \(\frac {1}{11}\) का व्युत्क्रम = \(\frac {11}{1}\) = 11, यह एक पूर्ण संख्या है।

प्रश्न 3.
ज्ञात कीजिए:
(i) \(\frac {7}{3}\) ÷ 2
(ii) \(\frac {4}{9}\) ÷ 5
(iii) \(\frac {6}{13}\) ÷ 7
(iv) 4\(\frac {1}{3}\) ÷ 3
(v) 3\(\frac {1}{2}\) ÷ 4
(vi) 4\(\frac {3}{7}\) ÷ 7
हल :

प्रश्न 4.
ज्ञात कीजिए :

हल :

Haryana State Board HBSE 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.4 Textbook Exercise Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 15 ठोस आकारों का चित्रण Ex 15.4

प्रश्न 1.
निम्नलिखित ठोसों के ठीक ऊपर एक जलता हुआ बल्ब रखा गया है। प्रत्येक स्थिति में प्राप्त छाया के आकार का नाम बताइए। इस छाया का एक रफ चित्र बनाने का प्रयास कीजिए। (पहले आप प्रयोग करने का प्रयास करें और फिर उत्तर दें।)

हल :
जब बल्ब ठोसों के ऊपर जलता हुआ रखा है :
गेंद : इसकी छाया वृत्त की तरह प्रतीत होगी।
बेलनाकार पाइप : इसकी छाया आयत की तरह प्रतीत होगी।
पुस्तक : इसकी छाया वर्ग की तरह प्रतीत होगी।

प्रश्न 2.
यहाँ कुछ 3-D वस्तुओं की छायाएँ दी गई हैं जो उन्हें एक ओवरहैड प्रोजेक्टर के लैम्प (बल्ब) के अन्तर्गत या नीचे रख कर प्राप्त की गई हैं। प्रत्येक छाया से मिलान वाले ठोस की पहचान कीजिए। (इनमें एक से अधिक उत्तर हो सकते हैं।)

हल :
प्रत्येक छाया से मिलान वाले ठोस निम्न हैं-
(i) एक गेंद, एक थाली आदि।
(ii) एक घन, पुस्तक आदि।
(iii) एक शंकु, आइसक्रीम कोन आदि।
(iv) एक बेलन, एक घनाभ आदि।

प्रश्न 3.
जाँच कीजिए कि क्या ये कथन सत्य हैं-
(i) एकघन एक आयत के आकार की छाया दे सकता है।
(ii) एक घन एक षड्भुज के आकार की छाया दे सकता है।
हल :
(i) सत्य
(ii) असत्य।

Haryana Board HBSE 7th Class Sanskrit Solutions रुचिरा भाग 2

• Chapter 1 सुभाषितानि
• Chapter 2 दुर्बुद्धिः विनश्यति
• Chapter 3 स्वावलम्बनम्
• Chapter 4 हास्यबालकविसम्मेलनम्
• Chapter 5 पण्डिता रमाबाई
• Chapter 6 सदाचारः
• Chapter 7 सड.कल्पः सिद्धिदायकः
• Chapter 8 त्रिवर्णः ध्वजः
• Chapter 9 अहमपि विद्यालयं गमिष्यामि
• Chapter 10 विश्वबंधुत्वम्
• Chapter 11 समवायो हि दुर्जयः
• Chapter 12 विद्याधनम्
• Chapter 13 अमृतं संस्कृतम्
• Chapter 14 अनारिकायाः जिज्ञासा
• Chapter 15 लालनगीतम्

Haryana State Board HBSE 7th Class Science Solutions Chapter 18 Wastewater Story Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 18 Wastewater Story

HBSE 7th Class Science Wastewater Story Textbook Questions and Answers

Question 1.
Fill in the blanks :
(a) Cleaning of water is a process of removing _________.
(b) Wastewater released by houses is called _________.
(c) Dried _________ is used as manure.
(d) Drains get blocked by _________ and _________.
Answer:
(a) pollutants
(b) sewage
(c) sludge
(d) chemicals, kitchenwaste.

Question 2.
What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Answer:
Sewage is a liquid containing wastes disposed off by household, industrial and agricultural, activities in water. It is dangerous to release untreated sewage in water because it can pollute the whole source of water. Sewage contain harmful substances and disease causing organisms. It is therefore, dangerous and unsafe to release untreated sewage in water.

Question 3.
Why should oils and fats be not realeased in the drain? Explain.
Answer:
Oils and fats should not be released in, the drains because they harden the soil in the pipes and block them. Fats get clogged in the holes of the soil in the drain and block it. It does not allow the wastewater to flow and thus the whole sewer system is blocked.

Question 4.
Describe the steps involved in getting clarified water from wastewater.
Answer:
Water is treated physically, chemically and biologically in wastewater treatment plant.
Following Steps are involved in the purification of water:
(i) At first stage all the physical impurities like stones, rags, napkins, plastic bags, cans, packets etc. are removed. It is done by passing the water through bar screens.

(ii) Then water is taken to grit and sand removal tank where impurities are removed by sedimentation.

(iii) Solids impurities and faeces etc. are collected from the bottom of the water. These solid impurities collected are called sludge. Water is cleared of floatable solids like oil and grease.

(iv) Clarified water is cleared of other impurities by aerator. All disease causing bacteria are removed by chlorination and water is released in various water bodies.

Question 5.
What is sludge? Explain how it is treated.
Answer:
Sludge is the collected solid waste from the wastewater during the treatment in water treatment plant. Sludge is decomposed in a separate tank by the anaerobic bacteria. Activated sludge is used as manure.

Question 6.
Untreated human excreta is a health hazard. Explain.
Answer:
Untreated excreta can cause a lot of health related problems. It pollutes soil, water and air. The polluted water contain disease causing bacteria, which can spread epidemics like cholera, meningities etc.

Question 7.
Name two chemicals used to disinfect water.
Answer:
Chlorine and ozone are the chemical used to clean the wastewater.

Question 8.
Explain the function of bar screens in a wastewater treatment plant.
Answer:
Bar screens clear the wastewater of all the physical impurities. Large waste objects like napkins, plastics, can sticks, rags etc. are, removed from the wastewater through the bar screens.

Question 9.
Explain the relationship between sanitation and disease.
Answer:
Sanitation and disease are related each other. It sanitation is there no disease will occur, but if the sanitation is not there various types of diseases will occur and spread. So sanitation should be kept to avoid diseases.

Question 10.
Outline your role as an active citizen in relation to sanitation.
Answer:
As active citizen we should take care of our personal and environmental sanitation. We should make people around us, aware of the benefits of sanitation we should help the municipal corporations and gram panchayats to cover all the open drains and remove the unhygenic and disease causing substances thrown in’open.

Question 11
Here is a crossword puzzle : “Good luck !

Across:
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body

Down:
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water
Answer:

Question 12.
Study the following statements about ozone:
(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its- proportion in air is about 3%.
Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four
Answer:
(b) and (c)

Extended Learning – Activities and projects

Question 1.
Construct a crossword puzzle of your own using the keywords.
Answer:
Do it yourself.

Question 2.
Then and now; Talk to your grand parents and other elderly people in the neighbourhood. Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief-report, on the information you collected.
Answer:
Do it yourself.

Question 3.
Visit a sewage treatment,plant.
It-could be as exciting and enriching as a visit to a zoo, a museum, or a park. To guide your observation here are a few suggestions.
Record in your notepad :
Place _________ Date _________ Time Name of the official at the plant _________ Guide/Teacher _________.
(a) The location of the sewage plant.
(b) Treatment capacity.
(c) The purpose of screening as the initial process.
(d) How is air bubbled through the aeration tank?
(e) How safe is the water at the end of the treatment? How is it tested?
(f) Where is the water discharged after treatment?
(g) What happens to the plant during heavy rains?
(h) Is biogas consumed within the plant or sold to other consumers?
(i) What happens to the treatment sludge?
(j) Is there any special effort to protect nearby houses from the plant?
(k) Other observations.
Answer:
Do it yourself.

HBSE 7th Class Science Wastewater Story Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Write different sources of wastewater?
Answer:
Household activities, industrial activities and agricultural activities.

Question 2.
Name certain organic impurities in the wastewater.
Answer:
Animal waste, Human faeces, oil and urine, fruits and vegetables.

Question 3.
Write certain Inorganic impurities in, the wastewater.
Answer:
Metals, phosphates and nitrates.

Question 4.
Name certain disease causing micro-organism.
Answer:
Bacterias, Viruses etc.

Question 5.
Which process removes the solids like faeces and other substances from the wastewater?
Answer:
Grit and sand removal tank.

Question 6.
Which instrument is used to remove floatable solids from the wastewater?
Answer:
A skimmer is used to remove floatable impurities.

Question 7.
Who decomposes the sludge?
Answer:
Anaerobic bacteria decompose the sludge.

Question 8.
What helps to clean the clarified water?
Answer:
Aerobic bacteria helps to clean the clarified water.

Question 9.
Why is ozone and chlorine used?
Answer:
Ozone and Chlorine is used to kill the bacteria etc. present in the clarified water.

Short Answer Type Questions

Question 1.
How is water’polluted?
Answer:
Water is used for various’purposes in homes, industries and agriculture. When water is used for cleaning, bathing, washing, dying etc. it pollutes the water. Unwanted waste materials and chemicals etc. get added in the water and this wastes the water.

Question 2.
How “bar screen” and ‘grit and sand removal tank’ help in clarification of water?
Answer:
When wastewater is passed through bar screens it separates big and large objects like plastics, bags, sticks, can, napkins etc. In grit and sand removal tank other solid impurities like pebbless and etc. are removed.

Question 3.
How is sludge treated?
Answer:
Sludge is the solid impurities separated from the sewage. It is removed and treated in a separate tank with anaerobic bacteria. During this process biogas is produced which is used to produce electricity. Dried sludge is used as manure.

Question 4.
What are the problem arising due to open drains and other unsanitary conditions?
Answer:
Open drains and unsanitary conditions produce bad smell. It becomes an idle place of breeding for mosquitoes, files and other harmful insects. These insects spread many harmful diseases and other health hazards.

Question 5.
How the kitchen waste blocks the drains?
Answer:
Kitchen waste like oils and fats clogs the pores in soil and reduce the Alteration process. It also blocks the pipes by hardening the pipes. Wastes like tealeaves solid food remains, cotton etc. also choke the pipes and slows down flow of oxygen. This slows down the decomposition process by the aerobic bacteria.

Long Answer Type Questions

Question 1.
How defection in open cause health hazards?
Answer:
Due to lack of proper sewage disposal system a large amount of people in India defecates in open. They use riverbeds, railway lines, fields and drains for this purpose. These excreta dries down and percolate, in soil with rain water. It pollutes the ground water. Excreate along river bed pollutes the river water. In this way water on the ground and under the ground get polluted. This polluted water contains the micro-organisms of various communicable diseases like cholera, typhoid, hepatilis and meningiti it is dysentry etc.

Wastewater Story Class 7 HBSE Notes

• Water is a precious natural resource.
• We cannot imagine our lives without water.
• We waste a lot of water daily in various household and industrial activities Such water is called wastewater.
• The wastewater produced during household acitivities, industrial activities and various agricultural processes is also called sewage.
• Sewage is the liquid waste which can cause various’diseases and environmental hazards if not managed.
• Sewage is collected from its sources and treated to destroy its harmful constituent to clean it.
• It is made usable in treatment plants and disposed off in various sources of water.
• Drainage system should be covered to avoid communicable diseases.
• We should not throw waste in open and should not defecate in open.
• Low cost disposal methods can be adopted in the areas where proper sewer system is not available.

Haryana State Board HBSE 7th Class Science Solutions Chapter 4 Heat Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 4 Heat

HBSE 7th Class Science Heat Textbook Questions and Answers

Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Laboratory Thermometer: While performing experiments involving measurement of temperature in the laboratory, a mercury thermometer is used. It is a thermometer having graduations marked on Celsius scale from 0°C to 100°C.

The difference between the lower and upper fixed points is called range of the thermometer. The range of a mercury thermometer is 100°C. A mercury thermometer having graduations from 0°C to 100°C is shown in figure 4.8.

Clinical Thermometer:
To measure the temperature of a person running fever, doctor uses a thermometer known as Clinicdl Thermometer. It is a specially designed mercury thermometer and is used in the clinics and hospitals by doctors to measure human body temperature.

In construction, it differs from laboratory thermometers, in the sense that a kink or constriction is provided in the stem just above the bulb. Because of this kink, mercury doesn’t fall back into the bulb when clinical thermometer is taken out of the mouth of a patient to know the temperature. A jerk is given to the thermometer so that it is set again for measuring human body temperature. The temperature interval marked on the clinical thermometers ranges from 35°C to 43°C.

Question 2.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors: aluminium, iron
Insulators: plastic, wood

Question 3.
Fill in the blanks:
(a) The hotness of an object is, is determined by its …………… .
(b) Temperature of boiling water cannot be measured by a …………… thermometer.
(c) Temperature is measured in degree ……………. .
(d) No medium is required for transfer of heat by the process of ………….. .
(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of …………. .
(f) Clothes of …………… colours absorb heat better than clothes of light colours.
Answer:
(a) Touching
(b) Clinical
(c) Celsius
(d) Radiation
(e) Conduction
(f) Dark

Question 4.
Match the following:

(i) Land breeze blows during	(a) summer
(ii) Sea breeze blows during	(b) winter
(iii) Dark coloured clothes are preferred during	(c) day
(iv) Light coloured clothes are preferred during	(d) night

Answer:

(i) Land breeze blows during	(d) night
(ii) Sea breeze blows during	(c) day
(iii) Dark coloured clothes are preferred during	(b) winter
(iv) Light coloured clothes are preferred during	(a) summer

Question 5.
Discuss why wearing more layers of clothing of during winter keeps us warmer tljian wearing just one thick piece of clothing?
Answer:
More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. As air is a bad conductor, it does not allow the body heat to escape out.

Question 6.
Look at Fig. 4.10. Mark where the heat is being transferred by conduction, by convection and by radiation.
Answer:

Question 7.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer:
In places of hot climate it is advised that the outer wail of houses be painted white because white colour do not radiate heat easily.

Question 8.
One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will he:
(a) 80°C
(b) More than 50°C but less than 80°C
(d) 20°C
(d) Between 30°C and 50°C
Answer:
(b) More than 50°C but less than 80°C

Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:
(a) Flows from iron ball to water.
(b) Not flow from iron ball to water or from water to iron ball.
(c) Flows from water to iron ball.
(d) Increase the temperature of both.
Answer:
(a) flows from iron ball to water.

Question 10.
A wooden spoon is dipped in a cup of ice-cream. Its other end:
(a) Becomes cold by the process of conduction.
(b) Becomes cold by the process of convection.
(c) Becomes cold by the process of radiation.
(d) Does not become cold.
Answer:
(d) does not become cold.

Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:
(a) Copper bottom makes the pan more durable.
(b) Such pans appear colourful.
(c) Copper is a better conductor of heat than the stainless steel.
(d) Copper is easier to clean than the stainless steel.
Answer:
(c) Copper is a better conductor of heat than the stainless steel.

Extended Learning – Activities And Projects

Question 1.
Go to a doctor or your nearest health centre. Observe the doctor taking temperature of patients. Enquire:
(a) Why he/she dips the thermometer in a liquid before use.
(b) Why the thermometer is kept under the tongue.
(c) Whether the body temperature can be measured by keeping the thermometer at some place other than mouth.
(d) Whether the temperature of different parts of the body is the same or different. You can add m.ore questions which come to your mind.
Answer:
Do yourself. You can take help of your family doctor.

Question 2.
Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.
Answer:
Do yourself.

Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.
Answer:
Do yourself.

Question 4.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permaganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Answer:
Do yourself.

HBSE 7th Class Science Heat Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is heat?
Answer:
The energy transferred from one body to another body due to a temperature difference between them is called heat.

Question 2.
Define temperature.
Answer:
Temperature is the degree of hotness or coldness of a body.

Question 3.
Define thermometer.
Answer:
A device used for measuring the temperature of different objects is called a thermometer.

Question 4.
Hot water bottles are used for fermentations. Explain why?
Answer:
Hot water bottles are used for fermentation as the water does not cool quickly due to its large specific heat capacity.

Question 5.
When equal amount of air, iron and oil are heated from 15°C to 25°C. List them in the order of increasing expansion.
Answer:
Iron, oil, air.

Question 6.
Name any four substances which expand on heating.
Answer:
Aluminium, steel, iron and copper.

Question 7.
Name any two substances which have negligible changes in length on heating.
Answer:
Pyrex glass, Invar.

Question 8.
Name two substances which contract on heating?
Answer:
Ice, Bismuth.

Question 9.
Do all liquids expand when heated or is there any exception?
Answer:
Yes, below 4°C when heated, water contract in stead of expanding.

Question 10.
Which substances has the highest heat capacity?
Answer:
Water.

Question 11.
What is the temperature of a normal human being on the Celsius scale?
Answer:
The temperature of a normal human being on the Celsius scale is 37°C.

Question 12.
Name the thermometer used for measuring the temperature of the human body.
Answer:
The thermometer used to measure the temperature of a human body is called clinical thermometer.

Question 13.
Define convection.
Answer:
The phenomenon due to which particles of a medium actually move to the source of heat energy and then move away from it after absorbing heat energy is called convection.

Question 14.
Why is convection not possible in solids?
Answer:
The molecules of a solid are held strongly due to intermolecular forces. As these molecules cannot travel to the source of heat energy, convection is not possible in case of solids.

Question 15.
What is ventilation?
Answer:
The process by which impure and warm air inside a room is continuously replaced by fresh air from outside is called ventilation.

Question 16.
What do you understand from the term lower standard point?
Answer:
The 0°C correspondence to the temperature of pure melting ice and is called the lower standard point.

Question 17.
What do you understand by upper standard point?
Answer:
100°C corresponds to the temperature of pure boiling water and is called the upper standard point.

Question 18.
Define conduction.
Answer:
The process of transmission of heat energy in solids without the actual movement of particles from their position is called conduction.

Question 19.
Give two examples to show that heat caused biological changes.
Answer:
(i) Conversion of ‘gur’ into alcohol.
(ii) Conversion of milk into curd.

Question 20.
Why is ice wrapped in gunny bags?
Answer:
Gunny bags have a number of fine pores, filled with air. Air being a bad conductor of heat does not allow the external heat to go in and melts the ice.

Question 21.
Why is tea generally served in China clay cups and plates?
Answer:
Because the China clay is bad conductor of heat and checks the heat conduction from the tea to the surroundings and thus keeps the tea hot.

Question 22.
By which of the processes (conduction, convection, radiation), it is not possible to transfer heat?
(i) In a vacuum
(ii) Through the solid material.
Answer:
(i) Conduction and convection
(ii) Convection and radiations.

Question 23.
Why do we use cooking utensils made of metals and alloys?
Answer:
Metals and alloys are good conductors of heat so that the heat from the flame is conducted to the food inside quickly and efficiently.

Question 24.
Is medium necessary for the transference of heat by radiations?
Answer:
No, medium is not necessary for the transference of heat by radiation.

Question 25.
Why do we feel warm while standing beside a burning furnace?
Answer:
When we stand beside a burning furnace, we feel warms, because of the heat radiation coming from the furnace.

Question 26.
Firemen wear helmets made from brass polished from outside. Why?
Answer:
Brass polished helmets reflects most of the heat and absorbs only a very little part of it when they fight against a fire.

Question 27.
When does the conduction of heat stop in two bodies in contact?
Answer:
The conduction of heat stops in two bodies in contact when both attain the same (equal) temperature. In this position they have no temperature difference.

Question 28.
Why is the handle of a press made of ebonite or wood?
Answer:
The handle of press is made of ebonite or wood, because ebonite and wood are bad conductors of heat. So the heat does not reach in our body.

Question 29.
Define radiation.
Answer:
The transfer of heat energy from a hot body to a cold body directly, without heating the space in between the two bodies is called radiation.

Question 30.
Define insulators.
Answer:
The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators.

Question 31.
What is thermos flask?
Answer:
Thermos flask is a device in which heat losses due to conduction, convention and radiation are minimised.

Short Answer Type Questions

Question 1.
The cooking utensils are made of metals like aluminium or copper while their handles are made of wood. Why?
Answer:
The cooking utensils are made of metals like aluminium or copper because these metals are good conductors of heat so they help in the transfer of heat.

The handles of cooking utensils are made up of bad conductors such as wood, plastic etc. As the handles made of bad conductors do not get heated up while cooking, we can hold them easily.

Question 2.
Kites and eagles fly without flapping their wings. Why?
Answer:
During the day, hot air surrounding the land gradually rises up and a convection air current develops. Kites and eagles move along this rising current without flapping the wings to fly high up in the sky.

Question 3.
Why do the birds puff up their feathers in winter?
Answer:
The birds puff up their feathers in winter, because in doing so they trap large amount of air, which in turn acts as an insulator and does not allow their body heat to flow out.

Question 4.
Explain briefly the formation of air currents.
Answer:
In coastal areas, during the day, the cool air blows from sea towmrds the land called sea breeze. During the night, the cool air blows from land to sea called the land breeze. This happens because of convection air currents. At night, land cools down much faster than sea. So, sea is warmer than land and the air current blows from land to sea. During the day, land is hotter than sea. As a result, the air rises up and cold air from sea blows towards the land to take its place.

Question 5.
Cement or concrete floors are made in pieces with metals or glass strips in between. Give reasons.
Answer:
It is done to allow for the expansion in summer and contraction in winter. If cement or concrete floors are made out in one continuous pieces. It would develop crackes due to contraction and expansion.

Question 6.
Room heaters have shiny reflectors. Why?
Answer:
Room heaters have shiny reflectors as the shiny surface absorbs very little heat. They reflect all the heat which makes the room heaters more effective.

Question 7.
Why is the handle of a pressure cooker covered with thick plastic?
Answer:
The handle of a pressure cooker covered with thick plastic, because plastic is a bad conductor of heat. Hence, the heat from the hot cooker does not flow to the handle, with the result that we can hold easily.

Question 8.
The desert sand is very hot in the day and very cool at night. Why?
Answer:
The desert sand has low specific heat capacity. So sand gets very hot in day time. During the night sand cools more quickly due to cold air which moves towards the sea.

Question 9.
Why is the handle of a metallic kettle covered with strips of cane?
Answer:
Cane strips is bad conductor of heat. Therefore, it cannot get heated when water is boiled in kettle. Therefore, the handle of a metallic kettle is covered with cane strips.

Question 10.
Why does the handle of an iron made of ebonite or wood?
Answer:
Ebonite or wood is a bad conductor of heat. Therefore, the heat from the iron is not conducted to the hand.

Question 11.
How does a blanket keep you warm in a cold night, even though it is not a source of heat?
Answer:
The blanket is made of wool, which is a bad conductor of heat. It has fine pores in which air is trapped which is also a bad conductor of heat. They do not allow heat to escape from our body to the surroundings. Therefore, the blanket keeps our body warm in winter.

Question 12.
Why are cloudy nights warmer than the clear nights?
Answer:
Cloudy nights are warmer than clear nights due to the fact that the heat which is radiated by the earth is again reflected back by the clouds. While on the other hand this phenomenon is not possible when the night is clear.

Question 13.
How are had conductors of heat useful in our daily life?
Answer:
Bad conductors are used for holding hot utensils in the kitchen. Bricks and mud which are bad conductors are used in building houses, especially in the ruler. regions. They keep houses warm in winter and cool in summer. The feathres of birds, hair and fur of animals keep them warm in winter, as they are bad conductor of heat.

Question 14.
Why do we wear woolen clothes in winter?
Answer:
Woolen clothes have fine pores filled with air. Wool and air are bad conductors of heat They do not allow heat of our bodies to escape out. Therefore woolen cloth keep the body warm in winter. And for the same reason we wear woolen cloth in winter.

Long Answer Type Questions

Question 1.
Describe briefly the process of conduction.
Answer:
Heat travels through solids by conduction only. The process of transmission of heat energy in solids without the actual movement of particles from their position is called conduction. Conduction takes place under the following conditions:
(i) A material medium that is compact.
(ii) No movement of any particle in the medium.
Thus, solids transmit heat though conduction. When a solid substance is heated, the particles that become hot start vibrating and pass on the excess energy to the neighbouring particles. This process continues till the whole body is heated. However during such an energy transfer, a particle does not change its position. Hence, heat is carried without the bodily movement of the particles.

There are some solids which allow the heat to pass through them. Such substances are called the conductors. Almost all metals such as iron, copper, silver, aluminium etc. are good conductors. The substances which do not allow the heat to pass through them are called the insulators. Wood, plastic, wool, clay etc. are bad conductors.

Question 2.
Write an experiment to prove that heat radiations can travel through vacuum.
Answer:
Take a flat bottomed flask. In the mouth of the flask fix a rubber stopper having two holes. Pass a thermometer through one hole and a glass tube with stopper through the other hole.

Remove air from the flask, by connecting to a vacuum pump. Record the temperature from the thermometer. Place the flask in bright sunlight or in front of an electric heater. It is observed that the thermometer records a rise in temperature. Thus, the experiment proves that transference of heat by radiaton requires no medium.

Question 3.
Explain the working of a thermos flask.
Answer:
Thermos flask is a special kind of flask for keeping liquids. It prevents loss or gain of heat by any of the three methods. It keeps liquid warm or cold for a long time. It was invented by Sir James Dewan in 1893.

It consists of a double-walled glass-cylinder. A vacuum is created in the space between the double walls. The two inner surfaces of glass walls are silvered. The flask is placed on a spring within a non-conduction cylindrical case to protect it from jerks and breakages. The gaps between flask and outer casing is packed with felt pads. The mouth of the flask is finally closed with a cork.

Since the container is made of glass which is a bad conductor of heat and therefore, the loss or gain of heat due to conduction is prevented. As there is vacuum between the double walls, it prevents transmission of heat by convection. Due to silvering of the inner surfaces, the heat loss by radiation is prevented. The cork and the felt pads also help to preserve the heat inside the flask. So, the hot liquids like tea, coffee, etc. remain hot and cold liquids like water, juice, etc. remain cold for a long time.

Question 4.
Write five applications of radiation.
Answer:
Applications of radiation:
(i) The base of cooking utensils is painted black so that it can absorb more heat and hence cooking is done fast.
(ii) Dark clothes are worn in winters as they absorb more heat from the sunlight and keep our body warm.
(iii) White clothes are worn in summer as they absorb very little heat and keep us cool.
(iv) Room-heaters have shiny reflectors as the shiny surface absorbs very little heat. They reflect all the heat which makes the room- heaters more effective.
(v) Crockeries are polished and painted white from outside so that they do not radiate heat easily.

Question 5.
Describe the process of radiation. How is it different from conduction and convection?
Answer:
Radiation is a process of transmission of heat in which heat energy travels in straight lines from hotter to cooler regions without the help of any intervening medium. It means that this process is different from the other two as it does not need any medium like conduction or convection. Radiation can take place in a vaccum. For example, heat from the sun reaches us through the outer space (vacuum) by means of radiation in the form of electromagnetic waves.

Differefnbe between radiation, conduction and convection:

Radiation	Conduction and convection
1. No medium is needed.	1. A medium is needed.
2. Heat energy is transferred in the form of electromagnetic waves.	2. In conduction, heat energy is transferred from particle to particle but in convection heat energy is transferred by the transfer of metres.
3. It is a fast mode of heat transfer.	3. It is a slow mode of heat transfer.
4. Medium (if any) is no heated.	4. Medium is heated.

Heat Class 7  HBSE Notes

• Our sense of touch is not always a reliable guide to the degree of hotness of an object.
• Heat: Heat is a form of energy which produces in us sensation of warmth. It causes hotness or coldness sensation in our body.
• Temperature: Temperature tells how hot a body is? Temperature of a body is the degree of hotness or coldness of the body.
• Heat flows in the direction of fall of temperature. Heat can be converted to other forms of energy like sound, light, mechanical energy etc. Other forms of energy can also be converted to heat energy.
• Effects of heat:
  (i) The object becomes hot.
  (ii) The object may expand in size.
  (iii) The object may change in state.
  (iv) Heat can speed up chemical reaction.
• Temperature is measured by a device called thermometer.
• The thermometer that measure our body temperature is called a clinical thermometer. The range of this thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from 10°C to 110°c.
• The laboratory thermometer used in laboratories. It is called Celsius thermometer. It has one hundred markings on it.
• The melting point of pure ice is called lower standard point. Its value is 0°C.
• The boiling point of pure water is called upper standard point. Its value is 100°C.
• Transfer of heat: Heat flows from one body to another body by temperature difference. The flow of heat is from higher temperature to lower temperature. There are three different ways of heat transfer: conduction, convention and radiations.
• Conduction of heat: The process in which heat is handed over from one particle to another in the direction of fall of temperature without the actual movement of the particles of the medium is called conduction.
  
• Good conductor of heat: The materials which allow heat to pass through them easily, are called good conductor of heat. For example, silver, copper, aluminium, mercury etc. are good conductors of heat.
• Bad conductor of heat: The materials which do not easily allow heat to pass through them are called bad conductors of heat or insulators. Wood, plastics, mud, cork, cotton, ebonite, asbestos, most gases and liquids are bed conductor of heat.
• Convention of heat: Convention is a process by which heat is transferred from one part of a substance to another part through the actual movement of its constituents particles (atoms or molecules). Only liquids and gases convert heat. A solid cannot do so because solids do not flow like liquids or gases do.
• Radiation of heat: The process by which heat travels from one body to another without the intervention of any material medium is known as radiation.
  All hot objects transfer heat by radiation. Radiation does not require either a conducting medium or a convecting fluid. The sun transfers heat in all directions through the process of radiation. The radiations absorbed or emitted by a body depends upon the colour of the body.
  
• Thermos Flask (Vacuum Flask): Thermos flask is used to keep things warm and cold. It consists of a double walled glass flask, having vacuum between the walls, kept inside metallic case with the cork supporters.
  The outer and inner surfaces of the glass flask are highly silvered. The mouth of flask is fitted with air tight cork.
  
  (i) The vacuum between the two walls of the flask prevent heat transfer by conduction or convection.
  (ii) The silver coating of the walls of the vessels reflects back heat radiations. Thus heat by radiation can neither enter inside the flask nor go out of the flask.
  (iii) The air-tight cork, which is bad conductor of heat prevents any loss of heat by conduction or convection.
  Some heat may be transferred by conduction through thin glass walls at the neck and the poorly conducting cork. Total transfer of heat is very-very small, thus hot or cold liquid kept inside will keep its temperature for a long time.

Haryana State Board HBSE 7th Class Science Solutions Chapter 3 Fibre to Fabric Textbook Exercise Questions and Answers.

Haryana Board 7th Class Science Solutions Chapter 3 Fibre to Fabric

HBSE 7th Class Science Fibre to Fabric Textbook Questions and Answers

Question 1.
You must be familiar with the following nursery rhymes:
(i) Baa baa black sheep, have you any wool
(ii) Mary had a little lamb, whose fleece was white as snow
Answer the following:
(a) Which parts of the black sheep have wool?
(b) What is meant by the white fleece of the lamb?
Answer:
(a) The Hair (fleece) of the black sheep have wool.
(b) The white fleece is the v/hite hair of the lamb.

Question 2.
The silkworm is (a) a caterpiller, (b) a Larva. Choose the correct option.
(i) a
(ii) b
(iii) both a and b
(iv) neither a nor b.
Answer:
(iii) both a and b.

Question 3.
Which of the following does not yield wool?
(i) Yak
(ii) Camel
(iii) Goat
(iv) Woolly dog.
Answer:
(iv) Woolly Dog.

Question 4.
What is meant by the following terms?
(i) Reasing
(ii) Shearing
(iii) Sericulture
Answer:
(i) The fleece of the sheep alongwith a thin layer of skin is removed from its body. This process is called shearing.
(ii) Silk fibres are also animal fibres. Silkworms spin the ‘silk fibres’.
(iii) The rearing of silkworms for obtaining silk is called sericulture.

Question 5.
Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.
Shearing, ………………. , sorting, ………………. , ………………. , ………………. , ………………. .
Answer:
Shearing, scouring, sorting, drying, dying, spinning, weaving.

Question 6.
Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk.
Answer:

(a) Female silkworm moth with eggs

Question 7.
Out of the following, which are the two terms related to silk production? Sericulture, Floriculture, Moriculture, Apiculture, Silviculture
Hints:
(i) Silk production involves cultivation of mulberry leaves and rearing silkworms.
(ii) Scientific name of mulberry is Morus alba.
Answer:
Sericulture, Moriculture.

Question 8.
Match the words of column I with those given in column II.

Column I	Column II
1. Scouring	(a) Yields silk fibres
2. Mulberry leaves	(b) Wool yielding animal
3. Yak	(c) Food of silk worm
4. Cocoon	(d) Reeling
	(e) Cleaning sheared skin

Answer:

Column I	Column II
1. Scouring	(e) Cleaning sheared skin
2. Mulberry leaves	(c) Food of silk worm
3. Yak	(b) Wool yielding animal
4. Cocoon	(a) Yields silk fibres

Question 9.
Given below is a crossword puzzle based on this lesson. Use hints to fill in the blank spaces with letters that complete the words.

Answer:

Extended Learning-Activities And Projects

Question 1.
Paheli wants to know the maximum length of continuous silk thread that can be obtained from a cocoon.
Answer:
Do yourself. Take help to your teacher.

Question 2.
Boojho wants to know why caterpillars need to shed their skin when they grow bigger but we humans do not.
Answer:
Do yourself.

Question 3.
Boojho wants to know why caterpillars should not be collected with bare hands.
Answer:
Do yourself.

Question 4.
Paheli wanted to buy a silk frock and went to the market with her mother. There they found that the artificial (synthetic) silk was much cheaper and wanted to know why Do you know why? Find out.
Answer:
Do yourself.

Question 5.
Someone told Paheli that an animal called ‘Vicuna’ also gives wooljl Can you tell her where this animal is found? Look for this in a dictionary or an encyclopaedia.
Answer:
Do yourself.

Question 6.
When handloom and textile exhibitions are held, certain stalls display real moths of various varieties of silk and their life histories. Try and visit these stalls with elders or teachers and see these moths and stages of their life history.
Answer:
Do yourself.

Question 7.
Look for eggs of any moth or butterfly in your garden or park or any other place full of plants. They look like tiny specks (dots) laid in a cluster on the leaves. Pull out the leaves containing eggs and-place them in a cardboard box. Take some leaves of the same plant or another plant of the same variety, chop them and put them in the box. Eggs will hatch into caterpillars, which are busy eating day and night. Add leaves everyday for them to feed upon. Sometimes you may be able to collect the caterpillars. But be careful. Use a paper napkin or a paper to hold a caterpillar.
Observe everyday. Note the
(i) number of days taken for eggs to hatch
(ii) number of days taken to reach the cocoon stage and
(iii) to complete life cycle. Record your observations in your notebook.
Answer:
Do yourself.

HBSE 7th Class Science Fibre to Fabric Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Name the sources of obtaining fibres.
Answer:
The sources of obtaining fibres are plants and animals.

Question 2.
Name some wool yielding animals.
Answer:
Some wool yielding animals are: sheep, angora goat, goat, yak, camel, llama, alpaca.

Question 3.
What is shearing?
Answer:
The fleece (hair) of the sheep alongwith a thin layer of skin is removed from its body. This process is called shearing.

Question 4.
From where do we get wool and silk fibres?
Answer:
Wool and silk fibres are obtained from animals. Wool is obtained from hair of animals ; as sheep hairs and silk fibtes are obtained from silk worm.

Question 5.
What is wool?
Answer:
Wool is the common name of applied to soft curly fibres obtained chiefly from the fleece of domesticated sheep.

Question 6.
What determines the fineness of wool?
Answer:
The number of crimps per centimetre determines the fineness of wool fibre.

Question 7.
Name two breeds of sheep which has finest fleece?
Answer:
Two breeds of sheep which has finest fleece are: merino and Karakul.

Question 8.
Name two systems used in the processing of wool.
Answer:
Two system used in the processing of wool are:
1. Woollen system
2. Worsted system.

Question 9.
Name two substance removed from row wool, before manufacturing yam.
Answer:
Two substance removed from raw wool, before manufacturing yarn are:
1. Yolk
2. Suint.

Question 10.
What is woolmark?
Answer:
Woolmark is the mark of standardisation given to woollen yarns and woollen products. This mark has been instituted by International Wool Secretariat (I.W.S.) located in North Yorkshire (U.K.).

Question 11.
What are the uses of wool?
Answer:
Wool is used for making fabrics, shawls, blankets, carpets, felt and upholstery.

Question 12.
Write the properties of wool fibre.
Answer:
Wool fibre is considerably resilient, has high tensile strength, light weight and is heat insulator.

Question 13.
Name the domesticated moth whose larva produces silk.
Answer:
Silk is obtained from the cocoon of the pupa of mulberry silk moth.

Question 14.
Name the plant on which silk larva feeds.
Answer:
Silk larva feeds on the leaves of mulberry tree.

Question 15.
Name the person responsible for the discovery of silk.
Answer:
Silk was discovered by Xi-Ling-Shi, the bride of Chinese emperor Huang Di, in about 3000 B.C.

Question 16.
Name the strongest variety of silk.State whether the variety you have named is wild silk or domesticated silk.
Answer:
The strongest variety of silk is “Muga”. It is the variety of wild silk.

Question 17.
Name the different varieties of processed silk.
Answer:
Organize, Gepe, Tram and Thrown Singles are different, varieties of processed silk.

Question 18.
Give uses of silk, other than for making dresses.
Answer:
Other than for making dresses, silk is used for items such as parachutes, bicycle tyres, bullet proof vests and non-absorbable sutures in surgery.

Question 19.
What is sericulture?
Answer:
The science of raising silkworms, so as to obtain silk cocoons, is called sericulture.

Question 20.
Where are sheep reared in India?
Answer:
In India sheep are reared in Sub-Himalyan region which has a cooler climate.

Question 21.
Differentiate between staple fibres and filament fibres.
Answer:
The fibres like cotton, jute, and wool are short in length. Silk however, is the longest natural fibre. The short fibres are known as the stable fibres, where as long fibres are known as the filament fibres.

Question 22.
Name some Indian breeds of sheep.
Answer:
Some Indian breeds of sheep are Lohi, Rampur bushair, Nali, Bakharwal, Marwari, and Patanwadi.

Question 23.
What is reeling of silk?
Answer:
A pile of cocoons is used for obtaining silk fibres. This process is called reeling of silk.

Short Answer Type Questions

Question 1.
Differentiate between woollen yarn and worsted yam.
Answer:
The woolen yarn is made from the woolen fibres of mixed lenghts. These fibres are, carded and spun to form a woolen yarn. The articles made from this yarn do not have smooth finished surface.

In the worsted yarn, only the long fibres are used. They are formed into smooth compact strands and are then spun to form woolen yarn. The articles made from these have smooth finished surface.

Question 2.
What do you mean by the term ‘weighting of sillf’?
Answer:
Silk when unwound from the cocoon is covered with a sticky substance. This has to be removed by washing process. As a result, silk loses about 20% of its weight. To make up for this loss some manufactures dip silk in metallic salt solution. This is known as weighting of the silk. This silk is weaker than pure silk. It than not be cleaned properly. This silk is of substandard quality and hence, deceives the buyers.

Question 3.
What is raw silk? How is it produced?
Answer:
After brushing, filaments from four to eight cocoons are joined and twisted. They are then combined with a number of other similarly twisted filaments, to make a thread that is wound on a reel. The thread is called raw silk.

It usually consists of 48 individual silk fibres. When each cocoon is unwound, it is replaced by another cocoon.Unlike the threads spun from other natural fibres, such as cotton or wool, the silk thread is made of extremely long fibres.

Question 4.
Name and describe any two types of silk threads used in the making of silk cloth.
Answer:
Two types of silk threads used in the making of silk cloth are:
1. Organzine:
Organzine thread is made by giving raw silk thread a preliminary twist in one direction and then twisting two or more of these threads in the opposite direction at rate of about 4 turns / cm.
2. Crepe: Crepe is similar to organzine, but it twisted to much greater extent, usually, 16 to 32 turns / cm.

Question 5.
Why do the wool fibres have greater bulk as compared to other fibres?
Answer:
The scales and crimps in the wool fibre make it possible to spin and felt the fleece. They help the individual wool fibres “grab” each other so that they stay together. Because of the crimp, wool fabrics have a greater bulk; than other textiles. They can retain lot of air and hence wool fabrics are good insulators of heat. The heat insulation also works boths ways.

Question 6.
Name the some breeds of sheep reared in our country. Also, indicate the quality and texture of the fibres obtained from them.
Answer:
Some Indian breeds of sheep:
Answer:

Name of breed	Quality of wool	State where found
1. Lohi	Good quality wool	Rajasthan, Punjab
2. Rampur bushair	Brown fleece	Uttar Pradesh, Himachal
3. Nali	Carpet wool	Rajasthan, Haryana, Punjab
4. Bakharwal	For woollen shawls	Jammu and Kashmir
5. Marwari	Coarse wool	Gujarat
6. Patanwadi	For hosiery	Gujarat

Question 7.
Write short note on ‘wool production’.
Answer:
Australia is the world’s largest producer of raw wool and contributes 29% of total world supply. Other leading producers of wool are former Soviet Republics, New Zealand, China, Argentina, South Africa and Uruguay. In India sheep are reared in Sub-Himalayan regions which has a cooler climate. The sheep which are reared in Rajasthan have poor quality of wool and are mainly reared for meat.

Long Answer Type Questions

Question 1.
What is raw silk? How is it produced?
Answer:
After brushing, filaments from four to eight cocoons are joined and twisted. They are then combined with a number of other similarly twisted filaments, to make a thread that is wound oft a reel. The thread is called raw silk. It usually consists of 48 individual silk fibres. When each cocoon is unwound, it is replaced by another cocoon. Unlike the threads spun from other natural fibres, such as cotton or wool, the silk thread is made of extremely long fibres. About 5,500 cocoons are required to produced 1 kg of raw silk.

Question 2.
What is sericulture? Explain in brief.
Answer:
The silk is obtained from cocoon. When the complete cocoon is formed, they are collected. The pupa inside the cocoon is killed by treating the cocoons with boiling water. This hot water not only kills the cocoons but also dissolves the sticky substance that holds the cocoon filaments in place. The cocoons are, thereafter, dried and brushed. This removes the outer portion that is made of coarse filaments.

The thread is then unwound from the cocoons and is wound on a reel. The thread is called the raw silk. It generally consists of 48 individual silk fibres. The silk filaments are unwound from cocoon in a manufacturing plant known as filature. The silk thread is made up of extremely long fibres. About 5,500 silkworms are needed to produce 1 kg of raw silk. The breeding and management of silk moths for producing silk is known as sericulture.

Question 3.
Explain briefly the process of wool manufacturing.
Answer:
In order to make different articles, the raw wool is processed which starts with sorting of the fibres. The fibres are sorted on the basis of length, fineness, etc. The sorting is followed by cleaning 6f the fibres. Using a suitable detergent, the fibres are cleaned from lanolin (an oily substance) and suint (the dried perspiration of sheep). The cleaned wool fibres are then dried and disentangled. Thereafter, they are drawn into a straight continuous thread. This process is called cerding. The kind of yarns that are produced may be woollen yarn or worsted yarn.

For the production oi wooiien yarn, the web is split into fine thin strands, by a process called roving. It is then spun into woollen yarn. Woollen fabric such as tweed is woven from woollen yarn. It is a bulky fabric in which short woollen fibres are arranged randomly. It does not have smooth surface.

For the production of worsted yam, the web is processed by the machines that (i) straighten the fibres (ii) make them parallel (iii) remove all the short fibres. The resultant woolen strand is then condensed by passing it through several machines, until a very thin strand of worsted roving is obtained. It is then spun to a smooth yarn.

Question 4.
What are the uses of wool? What is woolmark?
Answer:
Wool is used for making fabrics, shawls, blankets, carpets, felt (compressed wool) and upholstery. Wool felt is used to cover piano hammers. It is also used to absorb noise in heavy machinery and stereo speakers.

Shoddy is made from the used wool. To make shoddy, the existing wool fabric is cut into small pieces and then carddd. The carded wool is then respun into yarn. Such a yarn is inferior to the fresh wool and is used for making cheap woollen garments and blankets.

Woolmark:
Wool is marketed worldwide by the International Wool Secretariat (IWS), which is based in Ilkley, North Yorkshise (U.K.). The “Woolmark” instituted by IWS indicates that garments bearing this sign are made from pure new wool, that has not been used previously in any process.

Fibre to Fabric Class 7  HBSE Notes

• Wool comes from sheep, goat, yak and some other animals. These wool- yielding animals bear hair (fleece) on their body.
• The hairy skin of the sheep has two types of fibres that form its fleece : (i) the coarse beard hair, and (ii) the fine soft under hair close to the skin.
• The wool which is used for knitting sweaters or for weaving shawls is the finished product of a long process.
• Sheep hair is sheared off from the body, scoured, sorted, dried, dyed, spun and woven to yield wool.
• The hairs of camel, llama and alpaca are also processed to yield wool.
• The wool may be classified as Virgin, Hogg or pulled depending upon its quality.
• In wool production, Australia and New Zealand produce two-thirds of the world’s supply.
• Woolmark is the mark of standardisation given to pure and new wool.
• Silk fibres are also animal fibres. Silkworms spin the ‘silk fibres’. The rearing of silkworms for obtaining silk is called sericulture.
• The female silk moth lays eggs, from which hatch larvae which are called caterpillars or silkworms.
• During their life cycle, the worms spin cocoons of silk fibres.
• Silk fibres are made of a protein.
• Tassar silk, mooga silk, kosa silk, etc., are obtained from cocoons spun by different types of moths.
• The most common silk moth is the mulberry silk moth. The silk fibre from the cocoon of this moth is soft, lustrous and elastic and can be dyed in beautiful colours.
• Sericulture is a very old occupation in India. India produces plenty of silk on a commercial scale.
• A pile of cocoons is used for obtaining silk fibres. This process is called reeling of silk. The cocoons are kept under the sun or boiled or exposed to steam. The silk fibres separate out. The process of taking out threads from the cocoon for use as silk is called reeling the silk.

Haryana State Board HBSE 7th Class Maths Solutions Chapter 13 घातांक और घात InText Questions and Answers.

Haryana Board 7th Class Maths Solutions Chapter 13 घातांक और घात InText Questions

प्रयास कीजिए (पृष्ठ सं. 266)

प्रश्न 1.
ऐसे पाँच और उदाहरण दीजिए, जहाँ एक संख्या को घातांकीय रूप में व्यक्त किया जाता है। प्रत्येक स्थिति में, घातांक व आधार की पहचान भी कीजिए।
हल :
पाँच उदाहरण हैं :
(i) 2⁵ = 2 × 2 × 2 × 2 × 2 = 32
2⁵ में 2 आधार और 5 घातांक है।

(ii) 3⁵ = 3 × 3 × 3 × 3 × 3 = 243
3⁵ में 3 आधार और 5 घातांक है।

(iiii) 4³ = 4 × 4 × 4 = 64
4³ में 4 आधार और 3 घातांक है।

(iv) 2⁶ = 2 × 2 × 2 × 2 × 2 × 2
= 64
2⁶ में 2 आधार और 6 घातांक है।

(v) 7⁵ = 7 × 7 × 7 × 7 × 7
= 16807
75 में 7 आधार और 5 घातांक है।

पृष्ठ सं. 267

प्रश्न 1.
व्यक्त कीजिए :
(i) 729 को 3 की घात के रूप में
(ii) 128 को 2 की घात के रूप में
(iii) 343 को 7 की घात के रूप में
हल :
(i)

∴ 729 = 3 × 3 × 3 × 3 × 3 × 3
= 3⁶

(ii)

∴ 128 = 2 × 2 × 2 × 2 × 2 × 2 × 2 = 2⁷

(iii)

343 = 7 × 7 × 7 = 7³

पृष्ठ सं. 270

प्रश्न 1.
सरल करके घातांकीय रूप में लिखिए :
(i) 2⁵ × 2³
(ii) p³ × p2
(iii) 4³ × 4²
(iv) a³ × a² × a⁷
(v) 5³ × 5⁷ × 5¹²
(vi) (-4)¹⁰⁰ × (-4)²⁰
हल :
(i) 2⁵ × 2³ = 2^{5 + 3} = 2⁸
(ii) p³ × p² = p^{3 + 2} = p⁵
(iii) 4³ × 4² = 4^{3 + 2} = 4⁵
(iv) a³ × a² × a⁷ = a3 + 2 + 7 = a¹²
(v) 5³ × 5⁷ × 5¹² = 5^{3 + 7 + 12} = 5²²
(vi) (- 4)¹⁰⁰ × (- 4)²⁰ = (- 4)^{100 + 20}
= (-4)¹²⁰

पृष्ठ सं. 271

प्रश्न 1.
सरल करके घातांकीय रूप में लिखिए:
(उदाहरण के लिए, 11⁶ ÷ 11² = 11⁴)
(i) 2⁹ ÷ 2³
(ii) 10⁸ ÷ 10⁴
(iii) 9¹¹ ÷ 9⁷
(iv) 20¹⁵ ÷ 20¹³
(v) 7¹³ ÷ 7¹⁰
हल :
(i) 2⁹ ÷ 2³ = 2^{9 – 3} = 2⁶
(ii) 10⁸ ÷ 10⁴ = 10^{8 – 4} = 10⁴
(iii) 9¹¹ ÷ 9⁷ = 9^{11 – 7} = 9⁴
(iv) 20¹⁵ ÷ 20¹³ = 20^{15 – 13} = 20²
(v) 7¹³ ÷ 7¹⁰ = 7^{13 – 10} = 7³

पृष्ठ सं. 271

प्रश्न 1.
सरल करके, उत्तर को घातांकीय रूप में व्यक्त कीजिए-
(i) (6²)⁴
(ii) (2²)¹⁰⁰
(iii) (7⁵⁰)²
(iv) (5³)⁷
हल :
(i) (6²)⁴ = 6^{2 × 4}  = 68
(ii) (2²)¹⁰⁰ = 2^{2 × 100} = 2²⁰⁰
(iii) (7⁵⁰)² = 7^{50 × 2} = 7¹⁰⁰
(iv) (5³)⁷ = 5^{3 × 7} = 5²¹

पृष्ठ सं. 273

प्रश्न 1.
a^m × b^m = (ab)^m का प्रयोग करके, अन्य रूप में बदलिए :
(i) 4³ × 2³
(ii) 2⁵ × 5⁵
(iii) a² × t²
(iv) 5⁶ × (-2)⁶
(v) (-2)⁴ × (-3)⁴
हल :
(i) 4³ × 2³ = (4 × 4 × 4) × (2 × 2 × 2)
= (4 × 2) × (4 × 2) (4 × 2)
= (4 × 2)³

(ii) 2⁵ × b⁵ = (2 × 2 × 2 × 2 × 2) × (b × b × b × b × b)
= (2 × b) × (2 × b) × (2 × b) × (2 × b) × (2 × b)
= (2 × b)⁵ = (2b)⁵

(iii) a² × t² = (a × a) × (1 × 1)
= (a × t) × (a × t)
= (at) × (at) = (at)²

(iv) 5⁶ × (-2)⁶ = 5 × 5 × 5 × 5 × 5 × 5 × (-2 × – 2 × – 2 × – 2 × – 2 × – 2)
= (5 × -2) (5 × – 2) × (5 × – 2) × (5 × – 2) (5 × – 2) × (5 × – 2)
= (5 × – 2)⁶

(v) (-2)⁴ × (-3)⁴ = (- 2 × – 2 × – 2 × – 2) × (- 3 × – 3 × – 3 × 3)
= (- 2 × – 3) × (- 2 × – 3) × (- 2 × – 3) × (- 2 × – 3)
= (- 2 × – 3)⁴

पृष्ठ सं. 273

प्रश्न 1.
a^m ÷ b^m = \(\left(\frac{a}{b}\right)^{m}\) का प्रयोग करके, अन्य रूप में बदलिए:
(i) 4⁵ ÷ 3⁵
(ii) 2⁵ ÷ b⁵
(iii) (-2)³ ÷ b³
(iv) p⁴ + q⁴
(v) 5⁶ + (-2)⁶
हल :
a^m ÷ a^m = \(\left(\frac{a}{b}\right)^{m}\) का प्रयोग करने पर,

पृष्ठ सं. 277

प्रश्न 1.
10 की घातों का प्रयोग करते हुए, घातांकीय रूप में प्रसारित कीजिए :
(i) 172
(ii) 5643
(ii) 56439
(iv) 176428
हल :
(i) 172 = 1 × 100 + 7 × 10 + 2 × 1
= 1 × 10² + 7 × 10¹ + 2 × 10⁰

(ii) 5643 = 5 × 1000 + 6 × 100 + 4 × 10 + 3 × 1
= 5 × 10³ + 6 × 10² + 4 × 10¹ + 3 × 10⁰

(iii) 56439 = 5 × 10000 + 6 × 1000 + 4 × 100 + 3 × 10 + 9 × 1
= 5 × 104 + 6 × 10³ + 4 × 10² + 3 × 10¹ + 9 × 10⁰

(iv) 176428 = 1 × 100000 + 7 × 10000 + 6 × 1000 + 4 × 100 + 2 × 10 +8 × 1
= 1 × 10⁵ + 7 × 10⁴ + 6 × 10³ + 4 × 10² + 2 × 10¹ + 8 × 10⁰