HBSE 10th Class Science Important Questions Chapter 14 Sources of Energy

Haryana State Board HBSE 10th Class Science Important Questions Chapter 14 Sources of Energy Important Questions and Answers.

Haryana Board 10th Class Science Important Questions Chapter 14 Sources of Energy

Question 1.
Define source of energy. Which factors should be considered while selecting a source of energy? OR What is a good source of energy?
Answer:
Source of energy:

• A source from which useful energy can be extracted either directly or indirectly by means of a conversion or transformation is known as the source of energy.
• For example, sources of energy that provide us heat for cooking are LPG, kerosene, sunlight, etc.

Factors to consider while selecting an energy source:

• The source of energy should be available in good quantity.
• It should have good output i.e. it should be able to do a large amount of work per unit volume or mass.
• It should be easily accessible.
• It should be easy to store and transport.
• It should be economical.

Question 2.
What is a good fuel? OR What are the characteristics of a good fuel?
Answer:
Characteristics of a good fuel:

• The fuel should be cheap.
• It should be easily available and in good quantity.
• It should neither produce a lot of smoke nor leave a lot of residue.
•  It should have good thermal capacity.

Question 3.
As per the law, ‘Energy can neither be created nor destroyed.’ If this is true then why do we face so much energy crisis? Give one example.
Answer:
The law that energy can neither be created nor be destroyed is true. But energy in the usable form gets dissipated into the surroundings in the less usable form.
Example: When a candle is burnt it gives heat and light and releases some other substances. But, we cannot put together the heat, light and the substances to regain wax for using the candle again.

Question 4.
What do you mean by conventional and non-conventional sources of energy?
Answer:
The sources of energy available to us can be broadly classified as conventional and non-conventional.
(a) Conventional (Non-renewable) source of energy:
A source of energy which we cannot regenerate or reuse once we have used it is called a conventional or non-renewable source of energy.

Types: Fossil fuels such as coal, petroleum and natural gas, thermal power plants, hydro power plants, biomass and wind energy.

(b) Non-conventional (Renewable) source of energy:

• Those sources of energy which are inexhaustible or say can be renewed are called non-conventional (renewable) sources of energy.
• Solar energy, tidal energy, wind energy, geothermal energy, etc. are all examples of renewable sources of energy.

Question 5.
What do you mean by transformation of energy?
Answer:
The change in form of energy from one form to another is called transformation of energy. For example, transforming energy of wind to run an electric motor.

Question 6.
What is a fuel? Give examples.
Answer:
A substance which on burning gives heat and power is called fuel. -> Wood, coal, petrol, kerosene, CNG, PNG are all examples of fuels.

Question 7.
What are fossil fuels?
Answer:
Fuels such as coal, natural gas and petroleum formed in the earth crust due to decaying of plants and animal remains, millions of years ago are known as fossil fuels.

Question 8.
Why fossil fuels are called non-renewable?
Answer:
1. Fossil fuels are formed when dead plants and animals naturally get buried in the earth crust and remain there for millions of years.
2. Such material undergoes chemical changes for all these years due to the pressure and heat in the interior of earth.
3. Man has used a majority of the fossil fuels available in the earth just within few centuries. Naturally, man will not survive for another million years so as to use fossil fuels.
4. Since fossil fuel will soon become extinct, it is classified as non-renewable source of energy.

Question 9.
State the disadvantages of fossil fuels.
Answer:
Disadvantages of fossil fuels:

• Burning fossil fuels create smoke. This causes respiratory problems.
• Fossil fuels such as coal and petroleum cause severe air pollution.
• Acidic oxides of carbon, oxygen and sulphur are released on burning fossil fuels. These substances cause acid rain which affects our water and soil resources.
• Release of carbon dioxide leads to green house effect which causes global warming.

Question 10.
Explain in brief (a) Dynamo, (b) Turbine.
(a) Dynamo: Dynamo is a machine which converts mechanical energy into electrical energy by means of rotating copper coil in a magnetic field.

(b) Turbine:

• A turbine is a machine having a wheel or rotor which, on rotating, runs the dynamo and helps in generating electricity.
• The wheel of the turbine can be made to rotate by fast moving flow of steam, gas, water or air.

Question 11.
With the help of simple example, explain briefly how electricity as an energy is produced using turbine and dynamo.
Answer:
1. A turbine is made to rotate using either the flow of wind or water or steam.
2. The rotating shaft of the turbine is connected to the shaft of the dynamo/electric generator.
3. As shown, the force of steam from the cooker rotates the fan of the motor. This motion starts the motor. The shaft of the motor in-turn rotates the shaft of the dynamo. This generates electricity. The electricity produced can be supplied to run the electrical appliances such as bulb, fan, etc.

Working:

• Fuel such as coal is burnt to generate steam on a very large scale.
• The steam is directed to run the turbines which then generate electricity using generators.

Question 12.
What is a thermal power plant? How does it work?
Answer:
Thermal power plant is a set-up which converts heat energy into electrical energy on a large scale commercial basis. The electricity is then supplied to households as well as commercial establishments.

Question 13.
Write a note on production of electricity through hydropower plant.
Answer:
Hydropower plant:
Hydropower or hydroelectric plants use the potential energy of water stored at height (in dams) and the kinetic energy of the falling water for generating electricity. The power produced is called hydroelectricity or hydel electricity.

Process:

1. Huge dams having good heights are constructed to obstruct the flow of river water. The water is collected in these dams.
2. The water stored in these high dams possesses a huge quantity of potential energy.
3. The water is allowed to flow freely via pipes. The water from the pipes hit the turbine blades and rotates them. The turbine then runs the generator to produce electricity.
4. The water in the reservoirs gets filled with every rain and hence hydroelectricity is called a renewable source of energy.

Question 14.
Discuss the disadvantages of hydro-electric power plant.
Answer:
Disadvantages of hydro-electric power plant:
1. Dams for generating hydropower can be constructed only in some specific areas, preferably hilly areas.
2. Large agricultural areas and residential areas of people living in low areas get submerged in water.
So, such people have to be relocated. Relocating such people to a location suitable to them is also a major problem.
3. Large ecosystems get destroyed by getting submerged under dam water.
4. The vegetation that gets submerged becomes rotten due to anaerobic (lack of oxygen) condition.
As a result, a large quantity of methane gas gets released in the atmosphere. Methane gas is a greenhouse gas whose increased level causes global warming.

Question 15.
What is biomass? What can be done to obtain bio-energy using biomass?
Answer:
1. The waste material from plants or animals which is not used for food or feed is called biomass.
2. For example, dung is used as fuel, wood is also used as fuel. The source of these fuels i.e. plant and animal waste is then called biomass.
3. Plant residue left after farming, vegetable waste, etc. s also biomass.
4. These fuels have very low calorific value. Moreover, burning them produces lot of smoke.
5. We can produce bioenergy in the form of biogas using biomass.

Question 16.
Why there is a need of technological Intervention while using biomass as fuel?
Answer:
1. Cattle dung, wood, farm waste, etc. are all part of biomass and are used as fuel.
2. Wood on burning gives very less heat energy and also generates a lot of smoke. But, if wood is burnt in limited supply of oxygen, the water and volatile material present in the wood gets removed and what is left is called charcoal. Charcoal burns without flames or emitting heavy smoke like wood. It also gives more heat energy.
3. Similarly, cow dung, plant residues such as dead plants, dried leaves, residue obtained after harvesting a crop, vegetable waste and sewage can be gathered in a pit and decomposed in absence of oxygen to produce a more efficient fuel called biogas or gobar gas.
4. Thus, technological intervention improves fuel efficiency and also emits lesser or no pollutants in the environment.

Question 17.
What is biogas? State its advantages.
Answer:
1. The gas prepared by decomposing cow dung, plant residue such as dead plants, dried leaves, residue obtained after harvesting a crop, vegetable waste and sewage in a pit is called biogas or gobar gas.
2. Biogas is a mixture of gases namely methane, hydrogen, carbon dioxide and hydrogen sulphide.
3. Methane is the main constituent of biogas. 75% of biogas is methane.

Advantages of biogas:

•  Biogas is an excellent fuel which contains upto 75% methane. The gas is used for cooking purposes in villages.
• Biogas burns without smoke, leaves no residue like ash in wood and charcoal.
• It has a high thermal capacity.
• The slurry left behind as residue is an excellent manure rich in nitrogen and phosphorous.
• Biogas can also be used for lightening the villages.
• Biogas plant offers a large scale solution for effective utilization of bio-waste and sewage material.

Question 18.
Describe with a labeled diagram how biogas is produced in a fixed-dome type biogas plant.
Answer:
Structure of fixed-dome type biogas plant: Slurry

• This plant consists of an underground tank called the digester. The digester is made-up of bricks. It is a sealed chamber devoid of oxygen.
• The plant has a dome-shaped roof made of cement and bricks. This dome act as a gas holder.
• The dome has a gas outlet valve at the top for releasing biogas produced in the plant.
• There is a sloping inlet chamber on the left side of the digester tank. Raw material (bio-mass) is put in the plant from this inlet.
• On the right side there is an outlet chamber for removing residue from the plant.

Working:
1. Cow dung and water are mixed in a separate tank and are put into the digester of biogas plant via, the inlet chamber. (Note: If only cow dung is used in the plant, the plant can also be called as gobar-gas plant. However, a bio-gas plant can use other material over and above cow dung.)
2. The tank is then closed for few days.
3. During this period anaerobic micro-organisms (i.e. microorganisms that do not require oxygen) decompose or break down complex compounds of the cattle dung slurry.
4. The biogas starts getting collected in the dome. It is then brought out via, the outlet pipe of the dome.

Question 19.
Differentiate between biomass and bioas.
Answer:

Biomass (wood, cattle dung cakes, etc.)	Biogas
Using sources of biomass for fuel produces lot of smoke.	It does not produce smoke.
It leaves residue after burning which is of no use.	The residual slurry is excellent manure.
It has low calorific value.	It has high calorific value.

Question 20.
What is wind? Explain how wind energy Is used for doing work.
Answer:
1. Moving air is called wind.
2. Wind possesses kinetic energy. This kinetic energy can be used to do work or obtain electricity through a machine called wind mill.
3. The energy of the wind is used to rotate the blades of the wind mill. By connecting turbine with the windmill we can generate electricity.

Question 21.
Draw the structure of wind mill and explain how It works.
Answer:
Wind mill:

• The structure of wind mill can be compared to that of a large electric fan.
• It is erected at some height on a rigid support.
• A wind mill consists of three blades which rotate freely when wind blows through them.
• The shaft of the blade is further connected to the turbine and motor of electric generator.
• On rotating, the generator produces electric energy which is then supplied where needed.
• A single wind mill can generate only a small amount of energy. Hence, a number of wind mills are erected over a large area to produce electricity on large scale commercial basis. Such a set-up is called a wind farm.

Question 22.
State the advantages of wind mills.
Answer:
Advantages of wind mills:

• Wind energy does not cause any pollution.
• It is a renewable source of energy.
• Once installed, it does not cause any recurring expense.

Question 23.
What are the limitations of windmills or wind farms or energy obtained from wind?
Answer:
Limitations of a wind mill:

• Wind mill (or wind farm) can be established only at those places where wind blows for most of the year that too with a minimum speed of 15 km/h.
• A back-up facility such as storage cells is needed for continuous supply of electricity in case when there is no wind.
• A large area of land is needed to establish a wind farm.
  For example, 2 hectares of land would require to set-up a wind farm which would produce just 1 MW electricity.
• The initial cost to set-up a wind farm is quite high.
• The tower and the blades of the wind mill are always exposed to the vagaries of nature such as sun, rain, storm and cyclone. Hence, wind mills require a very high maintenance.

Question 24.
State the uses of wind mill.
Answer:
Uses of wind mill:

• The energy of wind mill is used to draw underground water with the help of water-lifting pump.
• It is used to rotate heavy stones for grinding wheat into flour.
• Wind mills are used to generate electricity.

Question 25.
What are alternate (non-conventional) sources of energy? Name few such energies.
Answer:
The sources of energy which we have not yet started using on a regular and routine basis are called non-conventional sources of energy.
Example: Solar energy, oceanic energy, geothermal energy and nuclear energy.

Question 26.
Give an introduction to solar energy.
Answer:
1. The energy obtained from the sun is called solar energy. This energy is available in two forms namely, light and heat.
2. The sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and it will continue to do so at same rate for another 5 billion years.
3. Out of the total energy that the sun emits, only a very small part of energy reaches the outer layer of earth’s atmosphere. 4. Out of this about 50% gets absorbed in the atmosphere and remaining half reaches the earth.

Question 27.
Explain the construction of solar cooker along with a diagram. Also state its uses.
Answer:

1. A solar cooker is a device which uses the energy of direct sunlight to heat and cook food.
2. The body of the solar cooker is made up of bad conductor material such as plastic or fibre.
3. The internal surface of the cooker and the containers used in it are of black colour to absorb maximum heat.
4. An adjustable plane mirror is fixed on the top of the box and it is adjusted in such a way that it can reflect maximum sunlight into the box.

Question 28.
Write a note on solar cells.
Answer:
1. Solar cells convert solar energy into electrical energy.
2. Solar cells are made up of silicon.
3. A typical solar cell develops a voltage of 0.5 -1 V and can produce about 0.7 W of electricity. Several such cells are joined together on one panel to obtain a large amount of electricity.

Question 29.
State the advantages of solar cells.
Answer:
Advantages of solar cells:

• Silicon which is the base material for making solar cells is available in abundance in the nature.
• Solar cells have no moving parts and so they require very less maintenance.
• These cells work quite efficiently without the need of any focusing device.
• Another big advantage is that solar panels can be set-up even in extremely remote and inaccessible areas where it is not feasible to set-up other sources of electricity.

Question 30.
Although solar power is an extremely useful mode of generating electricity, it comes with a host of limitations. Explain them.
Answer:
Limitations of solar cells (power):

• Silicon, the base material for solar cells is available in abundance but the special grade silicon needed for the cells is available only in limited quantity.
• The entire process of making the cell is quite costly. Moreover, usage of silver metals for interconnecting the cells further adds up to the cost.
• Owing to high cost, these cells cannot be used for domestic purpose.

Question 31.
Enlist the present day uses of solar cells.
Answer:
Present day uses of solar cells:

• Solar cells are used in artificial satellites and space probes like Mars orbiters.
• For operating electronic calculators, toys, etc.
• In remote area solar cells are used for domestic purpose to run street lights and to run radio and T.V.
• For operating traffic signals and in research centres.
• Solar cells are also used in cars at an experimental level.

Question 32.
Write a note on tidal energy.
Answer:
Tidal energy:

• The level of ocean water rises and falls due to the gravitational pull of moon on the earth.
• The rise of the ocean water is called the high tide whereas the fall is called low-tide.
• The difference in these tides give us energy which is called tidal energy.
• To obtain tidal energy, a tidal dam is built across the narrow opening of the sea. A turbine is fixed at the opening of the dam which converts tidal energy into electrical energy.

Limitations:
1. Tidal energy can be obtained only in coastal areas.
2. The electricity generated is in lesser quantity. So, its commercial use is not possible.

Question 33.
Give a brief idea about wave energy.
Answer:
Wave energy:

• The winds blowing over ocean produces waves. These waves possess large amount of kinetic energy.
• Several devices have been developed to trap wave energy for rotating the turbine and hence producing electricity.

Question 34.
What is OTEC ? Describe the working of an OTEC plant.
Answer:
Ocean Thermal Energy Conversion (OTEC):
Answer:
The energy available due to the difference in the temperature of water at the surface of the ocean and at deeper levels of the ocean is called Ocean Thermal Energy (OTE). The plant set-up to harnass this energy is called Ocean Thermal Energy Conversion (OTEC) Plant.

Working of an OTEC power plant :

1. The surface water of the ocean which remains hot due to sunlight possess higher temperature and hence works as the source of heat energy. The water below the surface remains comparatively colder i.e. it possess lower temperature.
2. The difference in temperature is used to obtain energy with the help of OTEC plant.
3. To run an OTEC plant the minimum temperature difference between the surface water and the water under it (upto 2 km) should be 20 °C. This temperature difference should be maintained through out the year.
4. Usually, an OTEC plant is erected inside the ocean, far away from the sea-shore.
5. The warm surface water is used to boil low-boiling liquid like ammonia. The vapours generated are then sent to move the turbine of generator.
6. The cold water from the deep ocean is used to cool the vapour that escaped from the turbine and is turned it into liquid for using again.

Question 35.
Explain the types of energy available from the sea.
There are three ways in which energy can be obtained from the sea. They are:
(1) Tidal energy, (2) Wave energy and (3) Ocean Thermal energy

Tidal energy:

• The level of ocean water rises and falls due to the gravitational pull or moon on the earth.
• The rise of the ocean water is called the high tide whereas the fall is called low-tide.
• The difference in these tides give us energy which is called tidal energy.
• To obtain tidal energy, a tidal dam is built across the narrow opening of the sea. A turbine is fixed at the opening of the dam which converts tidal energy into electrical energy.

Wave energy:

• The winds blowing over ocean produces waves. These waves possess large amount of kinetic energy.
• Several devices have been developed to trap wave energy for rotating the turbine and hence producing electricity.

Ocean Thermal Energy Conversion (OTEC):

• The energy available due to the difference in the temperature of water at the surface of the ocean and at deeper levels of the ocean is called Ocean Thermal Energy (OTE).
• The device used to obtain ocean thermal energy is known as Ocean Thermal Energy Conversion power plant or OTEC power plant.

Question 36.
What is geothermal energy? How is it produced?
Answer:
Geothermal energy:
1. The deep interior region of the earth where magma is found is very hot. The energy utilized from this heat is called geothermal energy.
2. The extremely high temperature in the interior of the earth melts the rocks present there. The molten substance is known as magma.
3. When geological changes take place, the magma gets pushed upwards. It then gets trapped in certain regions below the surface of the earth. These regions are called hotspots.
4. When the underground water comes in contact with the hotspots, it turns into steam.
5. Such regions are drilled and pipes are installed to draw high pressure steam into turbines installed on the ground. This rotates the turbine generator and electricity is produced.
6. At some places, steam and hot water ooze out on their own through cracks of the rocks. Such sites serve as hot water springs or natural geysers.
7. A number of power plants based on geothermal energy are in operation in New Zealand and America. Although it is cheap to obtain geothermal energy but there are very few locations that are commercially viable for generating this energy.

Question 37.
How is nuclear energy generated? State its advantages.
Answer:
1. When the nucleus of a heavy atom (such as uranium, plutonium or thorium) is bombarded with low-energy neutrons, it gets split into lighter nuclei. This process is called nuclear fission.
2. During the splitting of nucleus, tremendous amount of energy is released. This energy is called nuclear energy.
3. The mass of the original nucleus which is bombarded is slightly more than the sum of the masses of individual nucleus formed.
4. The released energy can be used to produce steam and hence generate electricity.

Advantages:

• The atomic fission of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
• The nuclear fuel can itself go on chain reaction and release energy at a controlled rate.

Question 38.
State the limitations of nuclear energy.
Answer:
Limitations of nuclear energy:

• The biggest problem is the storage and disposal of used nuclear fuel. The residual uranium in the used fuel keeps on decaying into harmful sub-atomic particles (radiations).
• Improper storage and disposal of nuclear waste contaminates the environment.
  In case of accident if the radiations leak, they can cause very large and widespread effect.
• The installation cost of nuclear power plant is very high. Uranium which is a raw material is not available inabundance. Add to these, the high risk of enviropmental contamination limits the use of nuclear energy for general purpose.

Question 39.
‘Irrespective of the energy source, the damage to environment takes place in some or the other form.’ Explain with reference to renewable sources of energy.
Answer:
1. Non-renewable sources cause a direct impact on environment that too at quite a fast pace.
2. In contrast to this we prefer alternative sources such as solar, CNG, hydro energy, etc. and call them clean fuels.
3. Although these fuels are clean but in fact they are not fully clean. They are just cleaner than the renewable sources.
4. Generating solar power needs solar cells for which we extract silicon from earth. Similarly, we need materials like plastic, glass, etc. to make solar devices. Manufacturing or extracting these things causes damage to the environment.
5. Similarly, for constructing dams thousands of trees are cut and ecosystems are destroyed. Moreover, cement, iron and steel and several such materials are needed to build up hydropower plant. All these things cause environmental pollution or degradation.

Question 40.
‘Manufacturers should produce high quality products that last long.’ Justify.
Answer:
1. In today’s time, manufacturers in order to earn more, have degraded the quality of their products.
2. The products now produced do not last long. As a result, people have to buy newer products in short span of time.
3. Whenever a product is manufactured it involves heavy degradation and pollution to environment. This leads to several problems such as rise in global warming, over-mining of resources, etc.
5. Hence, it is highly desirable that the products should be of good quality so that they last long and save environment.

Question 41.
Why is there a need to harness non-conventional sources of energy? Give two main reasons.
Answer:
There is need to harness non-conventional sources of energy due of the following reasons –
(1) The demand for energy is constantly rising due to

• Continuous rise in population,
• Our greed to improve the quality of life by adopting faster means of transportation, rapid industrialization and
• Extensive use of energy consuming appliances.

(2) The sources of energy which are available are mainly fossil fuels which are non-renewable sources. This means that these sources are limited and will soon exhaust.

Question 42.
What steps would you suggest to minimize environmental pollution caused by burning of fossil fuels?
Answer:
Some suggested steps to minimize environmental pollution caused by burning of fossil are –

• Make use of smokeless chulhas instead of burning wood for cooking.
• Increasing forest area.
• Using clean fuels like CNG, LPG, etc.
• By encouraging the use of public transport instead of private vehicles.
• By increasing the efficiency of combustion process such as that of vehicles, machines, etc.

Question 43.
Why are thermal power plants preferably set-up near coal or oil fields?
Answer:
1. Thermal power plants need coal in very large quantity and that too on a continuous basis.
2. If the plants are located near the coal mines the plants would save a considerable amount of money as well as time in transporting coal. This will also make electricity cheaper.

Question 44.
The use of dry wood as domestic fuel is not considered as a good fuel. State two reasons for it.
Answer:
1. Wood has very low calorific value and thermal capacity. So, by burning it we get very less heat for cooking.
2. Wood leaves a lot of residue and also releases a lot of smoke. This causes air pollution.

Question 45.
What are the two ways in which animal dung can be utilized as a fuel? Which of them is better?
Answer:
(a) Cattle dung can be dried to prepare cattle-dung cake. These cakes can be burnt to use as fuel.
(b) Animal dung can be used to produce biogas.
The second method is better because the gas produced does not cause pollution on burning. Moreover, the slurry left in the biogas plant is an excellent fertilizer.

Question 46.
What is the role of a plane mirror and a glass sheet in a solar cooker?
Answer:
(1) Role of plane mirror: Plane mirror is used as a reflector in solar cookers to focus the maximum rays of the sun into the cooker. This helps to achieve a higher temperature.

(2) Glass sheet: The glass sheet allows the infrared rays and visible rays to enter the solar cooker. The infrared rays then remain trapped in the cooker. This way the temperature of the cooker increases which helps in cooking food.

Question 47.
Why is the utility of solar cells less in spite of the fact that it is quite eco-friendly and self generating source of electricity ? OR Explain why the use of solar cells is limited.
Answer:
Silicon is the second largest element found in the earth’s crust.
1. But, for making solar cells a special grade of silicon is used which is available in very less quantity.
2. Moreover, to make internal connections in solar panel, silver is used which adds to the cost of production.
3. Even after doing all this we have not developed a very efficient system to store the electricity generated by these cells.
4. The electricity produced by these cells can be stored only in DC storage batteries.
5. When a gadget which runs on AC current is to be used, the DC current of the battery needs to be first converted into AC current. This leads to loss of some energy as well as increase in the cost.
6. Thus, due to all these reasons the use of solar cells become costly and impractical and so they are not widely used.

Question 48.
What is a wind farm? How it is better over a wind mill?
Answer:
1. A large area where several wind mills are erected so that electricity can be produced on a large scale is called a wind farm.
2. Since, the output of individual wind mill is quite less, installing several windmills together to create wind farm is a logical and better option.

Question 49.
State the advantages and disadvantages of geothermal energy.
Answer:
Advantages:

• It is cheaper to generate electricity from geothermal energy source.
• It is pollution free.

Disadvantages:

• There are very less places where geothermal energy is obtained.

1. Akruti heights is a posh high-rise residential society of Ahmedabad. There are 3 lifts per tower and the building is well lit with CFL lights. The monthly maintenance per flat pinches the members. So, a meeting was called and some members suggested to install solar power plant.

They explained that this would provide some electricity to light the building and any may reduce electric bill amount. They also said that this concept is environment-friendly. Now answer the following questions.

Questions:
1. Considering the high cost of solar panels and hence the solar power plant, do you think that the idea of installing solar plant is worth?
2. What are the disadvantages of appliances which run on solar energy?
3. What values have the society members displayed?
Answers:
1. Although setting up a solar power plant is costly. In the long-run, we can generate power free of cost. Hence, it is a good idea to install the solar plant.
2. Solar appliances do not work during cloudy and rainy days. Hence, the society will have to use the conventional modes of electricity.
3. The society members have displayed the values of betterment of all and awareness for conservation of fossil fuels.

2. On the suggestions of few friends, Rakesh decides to convert his petrol car into CNG. His wife Sudha works in a bank which falls on the way of Rakesh’s office. So, in most days Rakesh drops Sudha to her office as well as picks her up while coming home.

Rakesh’s son is in class 9. He studies in Holy Faith Boy’s School which is about 2.5 km from his house. So, rather than going through the school van, Rakesh insists his son to go to school on a bicycle. Now answer the following questions.

Questions:

1. Did Rakesh take a wise decision by converting his petrol car into CNG? Why/Why not?
2. Do you think switching to CNG can do any good to fossil fuels?
3. Rakesh insists that his son should go to school on a bicycle. In this tough times, where every minute counts do you think Rakesh should revoke his decision?
4. What value is reflected in this example?
Answers:
1. Yes. Rakesh took a wise decision by converting his car into CNG. Compared to petrol, CNG creates very less pollution. Moreover, it is quite reasonable. Hence, Rakesh can also save a good amount of money.
2. Fossil fuels are non-renewable and exhaustible sources of energy. Hence, by making use of CNG we can help in conserving fossil fuels.
3. The school is just 2.5 km from Rakesh’s house. So it will barely take 10 minutes for his son to reach the school. Although every minute counts in this competitive world, cycling such small distances can help to conserve environment which is equally the need of hour. Hence, Rakesh should not revoke his decision.
4. Rakesh has displayed values of a responsible citizen who cares Jor the environment. Sudha too has shown similar value.

3. In a summer afternoon, you find two cars belonging to your father parked in open. One of the cars is black coloured and has black film on window glass. The second car is white coloured. Moreover, it has plain window glass. For the purpose of an experiment, you open the door of each car one by one and sit inside for a while. Now answer the following questions.

Questions:
1. Which car is more hot from inside?
2. Discuss very briefly about the reason for variation of hotness of each car.
3. Suggest three ways for keeping the house cool in summer without making use of electricity.
Answers:
1. Black car is more hot as compared to the white car.
2. Black colour absorbs more heat as compared to white. Hence black car is more hot than the white car.
3. Suggestions to keep the house cool in summer:

• Put green curtain outside the window.
• Apply

Very Short Answer Type Question 

Question 1.
Define: Source of energy.
Answer:
A source from which useful energy can be extracted either directly or indirectly by means of a conversion or transformation is known as the source of energy.

Question 2.
State two factors while considering as energy source.
Answer:
(i) The energy source should give good output.
(ii) It should be easily available.

Question 3.
State two characteristics of a good fuel.
Answer:
(i) The fuel must be cheap
(ii) It should be easily available and in good quantity.

Question 4.
Define: Conventional source of energy.
Answer:
A source of energy which cannot be regenerated or reused once we have used it is called a conventional or non-renewable source of energy. For example, coal and petroleum.

Question 5.
Define: Non-conventional source of energy.
Answer:
Those sources of energy which are inexhaustible or say can be renewed are called non- conventional (renewable) sources of energy. For example, sun and wind.

Question 6.
Suggest two ways to reduce pollution caused by burning fossil fuels.
Answer:
1. Increasing the efficiency of combustion process
2. Using techniques to reduce the escape of harmful gases and ashes in the atmosphere and surroundings.

Question 7.
What is CNG?
Answer:
Full form of CNG is Compressed Natural Gas. It is used in vehicles as a cleaner fuel.

Question 8.
What is a dynamo?
Answer:
Dynamo is a machine which converts mechanical energy into electrical energy by means of rotating copper coil in a magnetic field.

Question 9.
What is a turbine?
Answer:
A turbine is a machine having a wheel or rotor which on rotating runs the dynamo and helps in generating electricity.

Question 10.
What is a thermal power plant?
Answer:
Thermal power plant is a set-up which converts heat energy into electrical energy on a large scale basis.

Question 11.
Where are fossil fuels used directly?
Answer:
In vehicles, gas-stoves, thermal power plant, etc.

Question 12.
How can you say that hydropower is renewable?
Answer:
Hydropower is generated due to water stored in dams. The dams get filled continuously with rain which keeps falling as per natural cycle.

Question 13.
Why it is not advised to use wood as a fuel in spite of the fact that forests can be replenished?
Answer:
Although forests can be replenished but it takes 15 years to grow a tree. Moreover, burning wood also causes pollution.

Question 14.
Why were hydroelectric plants of Tehri dams and Sardar Sarovar opposed?
Answer:
People residing on the land where these dams were proposed were to be relocated to a new area. People feared loss of home and farm land.

Question 15.
What is biomass?
Answer:
The waste material from plants or animals which is not use for food or feed is called biomass.

Question 16.
Why technological intervention is highly desired while using biomass as fuel?
Answer:
Technological improvement will increase the efficiency of using biomass fuels.

Question 17.
How is charcoal better than wood?
Answer:
Charcoal neither emits smoke nor does it burn with flames. Moreover, it also gives more heat energy as compared to wood.

Question 18.
List out the main gases formed in biogas.
Answer:
Methane (almost 75%), hydrogen, carbon dioxide and hydrogen sulphide.

Question 19.
Why biogas is also called gobar gas?
Answer:
The starting material for producing biogas is cow dung. Hence, biogas is also called gobar-gas.

Question 20.
State the biological process that takes place in the production of biogas.
Answer:
The anaerobic micro-organisms decompose the complex cow-dung and other material fed into the biogas plant and gives rise to biogas.

Question 21.
State the sequence of events occurring in a biogas plant.
Answer:
Feeding cow-dung and water into the plant → Breaking up of this material by anaerobic bacteria → Collection of biogas in the dome → Taking the gas out via. outlet pipe.

Question 22.
Which smokeless fuels can be used as domestic fuels?
Answer:
LPG, PNG, biogas and kerosene.

Question 23.
Define: Wind.
Answer:
Moving air is called wind.

Question 24.
What is a wind farm?
Answer:
A set-up where several wind mills are installed for generating electricity on a large scale is called a wind farm.

Question 25.
State the traditional uses of wind and water energies.
Answer:
Traditionally, wind and water energies were used to carry out basic tasks such as sailing boats, separating husk from grain, watering farms using water-wheel, etc.

Question 26.
What is the function of the glass plate of a solar cooker?
Answer:
The glass plate allows the sun-rays to enter. At the same time, the plate trap the heat formed inside the cooker.

Question 27.
How much electrical energy does a solar cell produce?
Answer:
A typical solar cell develops a voltage of 0.5 V to 1 V and can produce about 0.7 W of electricity.

Question 28.
Why solar cells are almost maintenance-free?
Answer:
Solar cells have no moving part and so they are almost maintenance free.

Question 29.
What is the biggest advantage of solar cells?
Answer:
A solar panel can be installed in almost any remote and inaccessible area that too for very small use for an individual person.

Question 30.
What is tidal energy?
Answer:
The energy harnessed from the difference in high-tide and low tide is called tidal energy.

Question 31.
What is OTE?
Answer:
OTE or Ocean Thermal Energy is the type of energy harnessed from the temperature difference of the ocean water at surface level and water below it.

Question 32.
Name the forms in which energy from oceans can be obtained?
Answer:
Tidal energy, wave energy and Ocean Thermal Energy (OTE).

Question 33.
Which is the most feasible source of oceanic energies? Why?
Answer:
Ocean thermal energy conversion is the most feasible because unlike wave and tidal energies, OTE can be harnessed at several locations. Moreover, its plant can be operated for 24 hours throughout the year.

Question 34.
What is geothermal energy?
Answer:
The deep interior region of the earth where magma is found is very hot. The energy utilized from this heat is called geothermal energy.

Question 35.
What is nuclear fission?
Answer:
When the nucleus of a heavy atom (such as uranium, plutonium or thorium) is bombarded with low-energy neutrons, it gets split into lighter nuclei. This process is called nuclear fission.

Question 36.
Compare the nuclear fission that takes place in a nuclear weapon and a nuclear reactor.
Answer:
The fundamental physics of the fission chain reaction in both is similar. However, the two types of devices work on very different engineering structures.

Fill in the Blanks

1. ………… gas is responsible for greenhouse effect.
Answer:
Carbon dioxide

2. ………….. is the mechanical device needed to generate power from wind and water both.
Answer:
Turbine

3. Mostly a thermal power plant would be located near …………..
Answer:
Coal or oil field

4. You will get if you burn wood in limited supply of oxygen.
Answer:
Charcoal

5. …………………. is the primary source of fuel of modern world.
Answer:
Fossil fuel

6. ……………. decompose the complex compound of cow-dung slurry.
Answer:
Anaerobic microorganisms

7. Winds blow due to the process of ………….
Answer:
Unequal heating of landmass and water mass by solar radiation causing movement of air.

8. The structure of a windmill can be compared with that of a ……………
Answer:
Fan

9. The minimum speed of wind in order to run a wind mill is…………..
Answer:
15 km/h

10. 2 hectare of land will produce ………….. electricity with the help of windmills.
Answer:
1 MW

11. As per an estimate the sun’s total years of radiating light are ……………
Answer: 10 billion

12. One of the ways to increase solar radiation in a solar cooker is………….
Answer: Using mirrors to focus the sun rays.

13. A typical solar cell produces Watts.
Answer: 0.7

14. The biggest advantage of solar cells is ………….
Answer:
They can be installed in the most remote location even for a single person.

15. ………..is the base material for making a solar cell.
Answer:
Silicon

16. Solar cells are capable to provide electricity to one such area where no other non-conventional source can. The area is …………
Answer:
Artificial satellites and space probes.

17. OTE works on the principle of ……………..
Answer:
Difference in water temperature.

18. For OTE, the temperature difference between water should be ………..
Answer:
Minimum 20°C

19. The fission of uranium produces ……………. times the energy by combustion of an carbon atom of coal.
Answer:
10 million.

True Or False

1. The total energy in any physical or even chemical process remains the same. — True
2. Burning coal was the most common source of energy in the ancient times. — False
3. Bangalore and Shimla can obtain electricity from similar source. — False
4. Apart from providing electricity for almost free,it is quite cheap to set-up a wind mill. — False
5. Transmission of electricity is more efficient than transportation sources such as coal and petroleum. — True
6. A quarter of our energy requirement in india is met by hydro power plants. — True
7. The domestic use of solar cells in limited owing to its high maintenance. — False
8. Nuclear fuel can behave as a self-sustaining fission chain reaction that releases energy at a controlled rate. — True
9. The fundamental physics in which the fission chain reaction of a nuclear weapon occurs and that of a nuclear reactor is quite different. — False

Match the Following

Question 1.

Column I.	Column II
(1) Causes suffocation and headache	(A) Carbon dioxide
(2) Green house effect	(B) Nitrogen dioxide
(3) Acid Rain	(C) Sulphur dioxide
(4) Smog	(D) Carbon monoxide

Answer: 1-D, 2-A, 3-C, 4-B

Question 2.

Column I	Column II
(1) Component of sunlight which carries, heat energy	(A) Sulphur dioxide and nitrogen dioxide
(2) Gases responsible for acid rain	(B) Hydrogen
(3) Proceés which converts solar energy into chemical energy	(C) Photosynthesis
(4) Burns with explosion	(D) Infrared

Answer: 1-D, 2-A, 3-C, 4-B