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Chapter 14

Sources of Energy

In-Chapter Exercise

Question 1:

What is a good source of energy? 

Answer:

A good source of energy fulfils the following criteria:

  1. It produces a lot of heat per unit mass.
  2. It does a huge amount of work per unit mass.
  3. It is easily accessible.
  4. It is easy to store and transport. 

  (V)    It is economical.

  (VI)   It produces less amount of smoke.

*Question 2:

What is a good fuel? 

Answer:

A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.

*Question 3:

If you could use any source of energy for heating your food, which one would you use and why?

Answer:

Natural gas can be used for heating and cooking food because it is a clean source of energy. It does not produce a huge amount of smoke on burning. Although it is highly inflammable, it is easy to use, transport, and it produces a huge amount of heat on burning.

In-Chapter Exercise

Question 1:

What are the disadvantages of fossil fuels? 

Answer:

The disadvantages of fossil fuels are as follows:

  1. Burning of coal and petroleum produces a lot of pollutants causing air pollution.
  2. Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and potable water.
  3. Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.

Question 2:

Why are we looking at alternate sources of energy? 

Answer:

Fossil fuels, which have been traditionally used by human beings as an energy sources, are non-renewable sources of energy. These sources of energy are limited and cannot replenish on their own. They are being consumed at a large rate. If this rate of consumption continues, then the fossil fuels would be exhausted from the Earth. Therefore, we have to conserve the energy sources. Hence, we should look for alternate sources of energy.

Question 3:

How has the traditional use of wind and water energy been modified for our convenience?

Answer:

Traditionally, waterfalls were used as a source of potential energy which was converted to electricity with the help of turbines. Since waterfalls are few in number, water dams have been constructed in large numbers. Nowadays, hydro-dams are used in order to harness potential energy of stored water. In water dams, water falls from a height on the turbine, which produces electricity.

Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting/drawing water from a well. Today, windmills are used to generate electricity. In windmills, the kinetic energy of wind is harnessed and converted into electricity. The rotatory motion of the blades turns the turbine of the electric generator to generate electricity.

In Chapter Exercise

*Question 1:

What kind of mirror − concave, convex or plain − would be best suited for use in a solar cooker? Why?

Answer:

A solar cooker uses heat of the sunlight to cook and heat food. A mirror is used in order to reflect and focus sunlight at a point. A concave mirror is used in a solar cooker for this purpose. The mirror focuses all the incident sunlight at a point. The temperature at that point increases, thereby cooking and heating the food placed at that point.

Question 2:

What are the limitations of the energy that can be obtained from the oceans? 

Answer:

The forms of energy that can be obtained from the ocean are tidal energy, wave energy, and ocean thermal energy. There are several limitations in order to harness these energies.

  1. Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
  2. High dams are required to be built to convert tidal energy into electricity.
  3. Very strong waves are required to obtain electricity from wave energy.
  4. To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20ºC or more.

Question 3:

What is geothermal energy? 

Answer:

Geothermal power plants use the heat of the Earth to generate electricity. This heat energy of the Earth is known as geothermal energy.

When there are geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. This forms regions of hotspots. Steam is generated when the underground water comes in contact with these hot spots forming hot springs. This trapped steam is used to generate electricity in the geothermal power plants.

*Question 4:

What are the advantages of nuclear energy? 

Answer:

The advantages of nuclear energy are as follows:

  1. Large amount of energy is produced per unit mass.
  2. It does not produce smoke. It is clean energy.
  3. Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon.
  4. Fusion of four hydrogen atoms produces a huge amount of energy approximately equal to 27 MeV.

In-Chapter Exercise

*Question 1:

Can any source of energy be pollution-free? Why or why not? 

Answer:

No source of energy can be pollution-free. It is considered that solar cells are pollution- free. However, even their making causes environmental damage indirectly.

Also, in the case of nuclear energy, there is no waste produced after the  fusion reactions. However, it is not totally pollution-free. To start the fusion reactions, approximately 107 K temperature is required, which is provided by fission reactions. The wastes released from fission reactions are very hazardous. Hence, no source of energy is pollution-free.

*Question 2:

Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Answer:

Hydrogen gas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon contents. Carbon is a form of pollutant present in CNG. On the other hand, hydrogen is waste-free. The fusion of hydrogen does not produce any waste. Hence, hydrogen is cleaner than CNG.

In-Chapter Exercise

Question 1:

Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Answer:

Two renewable sources of energy are as follows:

  1. Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium, fusion of helium into other heavy elements, and so on. A large amount of hydrogen and helium is present in the Sun. Therefore, solar energy can replenish on its own. The Sun has 5 billion years more to burn. Hence, solar energy is a renewable source of energy.
  2. Wind: Wind energy is derived from air blowing with high speed. Wind energy is harnessed by windmills in order to generate electricity. Air blows because of uneven heating of the Earth. Since the heating of the Earth will continue forever, wind energy will also be available forever.

Question 2:

Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Answer:

Two exhaustible energy sources are as follows:

  1. Coal: It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non renewable or exhaustible source of energy.
  2. Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the Earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.

Last Exercise

Question 1:

A solar water heater cannot be used to get hot water on

(a) a sunny day (b) a cloudy day

(c) a hot day (d) a windy day 

Answer:

(b) A solar water heater uses solar energy to heat water. It requires bright and intense sunlight to function properly. On a cloudy day, the sunlight reflects back in the sky from the clouds and is unable to reach the ground. Therefore, solar energy is not available for the solar heater to work properly. Hence, solar water heater does not function on a cloudy day.

Question 2:

Which of the following is not an example of a biomass energy source?

(a) wood (b) gobar gas

(c) nuclear energy (d) coal 

Answer:

(c) Biomass is a source of energy that is obtained from plant materials and animal wastes. Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. This reaction produces tremendous amount of energy. Hence, nuclear energy is not an example of biomass energy source.

Wood is a plant material, gobar gas is formed from animal dung, and coal is a fossil fuel obtained from the buried remains of plants and animals. Hence, these are biomass products.

*Question 3:

Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

  1. Geothermal energy
  2. Wind energy
  3. Nuclear energy
  4. Biomass

Answer:

(c) Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atoms are bombarded with low-energy neutrons. Hence, the uranium atom splits into two relatively lighter nuclei. This reaction produces a huge amount of energy. In nuclear fusion reactions, lighter nuclei are fused together to form a relatively heavier nuclei. The energy required to fuse the lighter nuclei is provided by fission reactions. 

This reaction produces a tremendous amount of energy. These reactions can be carried out in the absence or presence of sunlight. There is no effect of sunlight on these reactions. Hence, nuclear energy is not ultimately derived from the Sun’s energy.

Geothermal energy, wind energy, and biomass are all ultimately derived from solar energy.

Geothermal energy is stored deep inside the earth’s crust in the form of heat energy. The heating is caused by the absorption of atmospheric and oceanic heat. It is the sunlight that heats the atmosphere and oceans.

Wind energy is harnessed from the blowing of winds. The uneven heating of the earth’s surface by the Sun causes wind.

Biomass is derived from dead plants and animal wastes. Chemical changes occur in these dead plants and animal wastes in the presence of water and sunlight. Hence, bio- mass is indirectly related to sunlight.

Question 4:

Compare and contrast fossil fuels and the Sun as direct sources of energy. 

Answer:

Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath the Earth’s crust. They are directly available to human beings for use. Hence, fossil fuels are the direct source of energy. These are limited in amount. These are non-renewable sources of energy because these cannot be replenished in nature. Fossil fuels take millions of years for their formation. If the present fossil fuel of the Earth gets exhausted, its formation will take several years. Fossil fuels are also very costly.

On the other hand, solar energy is a renewable and direct source of energy. The Sun has been shining for several years and will do so for the next five billion years. Solar energy is available free of cost to all in an unlimited amount. It replenishes in the Sun itself.

Question 5:

Compare and contrast biomass and hydroelectricity as sources of energy.

Answer:

Biomass and hydro-electricity both are renewable sources of energy. Biomass is derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the result of natural processes. Wood, gobar gas, etc. are some of the examples of bio- mass.

Hydro-electricity, on the other hand, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.

Question 6:

What are the limitations of extracting energy from −

(a) the wind? (b) waves? (c) tides? 

Answer:

  1. Wind energy is harnessed by windmills. One of the limitations of extracting energy from wind is that a windmill requires wind of speed more than 15 km/h to generate electricity. Also, a large number of windmills are required, which covers a huge area.
  2. Very strong ocean waves are required in order to extract energy from waves.
  3. Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.

Question 7:

On what basis would you classify energy sources as

  1. renewable and non-renewable?
  2. exhaustible and inexhaustible?

Are the options given in (a) and (b) the same? 

Answer:

(a) The source of energy that replenishes in nature is known as a renewable source of energy. Sun, wind, moving water, biomass, etc. are some of the examples of renewable sources of energy.

The source of energy that does not replenish in nature is known as a non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non- renewable sources of energy.

(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.

Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Biomass is one of the inexhaustible sources of energy.

Yes. The options given in (a) and (b) are the same.

*Question 8:

What are the qualities of an ideal source of energy? 

Answer:

An ideal source of energy must be:

  1. Economical
  2. Easily accessible
  3. Smoke/pollution free
  4. Easy to store and transport
  5. Able to produce huge amount of heat and energy on burning

Question 9:

What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Answer:

Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amount. Hence, operating a solar cooker is not expensive.

Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy day, it becomes useless.

The places where the days are too short or places with cloud covers round the year, have limited utility for solar cooker.

Question 10:

What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Answer:

Industrialization increases the demand for energy. Fossil fuels are easily accessible sources of energy that fulfil this demand. The increased use of fossil fuels has a harsh effect on the environment. Too much exploitation of fossil fuels increases the level of green house gas content in the atmosphere, resulting in global warming and a rise in the sea level.

It is not possible to completely reduce the consumption of fossil fuels. However, some measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.

Chapter 14

Sources of Energy

In-Chapter Exercise

Question 1:

What is a good source of energy? 

Answer:

A good source of energy fulfils the following criteria:

  1. It produces a lot of heat per unit mass.
  2. It does a huge amount of work per unit mass.
  3. It is easily accessible.
  4. It is easy to store and transport. 

  (V)    It is economical.

  (VI)   It produces less amount of smoke.

*Question 2:

What is a good fuel? 

Answer:

A good fuel produces a huge amount of heat on burning, does not produce a lot of smoke, and is easily available.

*Question 3:

If you could use any source of energy for heating your food, which one would you use and why?

Answer:

Natural gas can be used for heating and cooking food because it is a clean source of energy. It does not produce a huge amount of smoke on burning. Although it is highly inflammable, it is easy to use, transport, and it produces a huge amount of heat on burning.

In-Chapter Exercise

Question 1:

What are the disadvantages of fossil fuels? 

Answer:

The disadvantages of fossil fuels are as follows:

  1. Burning of coal and petroleum produces a lot of pollutants causing air pollution.
  2. Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which affects the soil fertility and potable water.
  3. Burning of fossil fuels produce gases such as carbon dioxide that causes global warming.

Question 2:

Why are we looking at alternate sources of energy? 

Answer:

Fossil fuels, which have been traditionally used by human beings as an energy sources, are non-renewable sources of energy. These sources of energy are limited and cannot replenish on their own. They are being consumed at a large rate. If this rate of consumption continues, then the fossil fuels would be exhausted from the Earth. Therefore, we have to conserve the energy sources. Hence, we should look for alternate sources of energy.

Question 3:

How has the traditional use of wind and water energy been modified for our convenience?

Answer:

Traditionally, waterfalls were used as a source of potential energy which was converted to electricity with the help of turbines. Since waterfalls are few in number, water dams have been constructed in large numbers. Nowadays, hydro-dams are used in order to harness potential energy of stored water. In water dams, water falls from a height on the turbine, which produces electricity.

Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting/drawing water from a well. Today, windmills are used to generate electricity. In windmills, the kinetic energy of wind is harnessed and converted into electricity. The rotatory motion of the blades turns the turbine of the electric generator to generate electricity.

In Chapter Exercise

*Question 1:

What kind of mirror − concave, convex or plain − would be best suited for use in a solar cooker? Why?

Answer:

A solar cooker uses heat of the sunlight to cook and heat food. A mirror is used in order to reflect and focus sunlight at a point. A concave mirror is used in a solar cooker for this purpose. The mirror focuses all the incident sunlight at a point. The temperature at that point increases, thereby cooking and heating the food placed at that point.

Question 2:

What are the limitations of the energy that can be obtained from the oceans? 

Answer:

The forms of energy that can be obtained from the ocean are tidal energy, wave energy, and ocean thermal energy. There are several limitations in order to harness these energies.

  1. Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.
  2. High dams are required to be built to convert tidal energy into electricity.
  3. Very strong waves are required to obtain electricity from wave energy.
  4. To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20ºC or more.

Question 3:

What is geothermal energy? 

Answer:

Geothermal power plants use the heat of the Earth to generate electricity. This heat energy of the Earth is known as geothermal energy.

When there are geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. This forms regions of hotspots. Steam is generated when the underground water comes in contact with these hot spots forming hot springs. This trapped steam is used to generate electricity in the geothermal power plants.

*Question 4:

What are the advantages of nuclear energy? 

Answer:

The advantages of nuclear energy are as follows:

  1. Large amount of energy is produced per unit mass.
  2. It does not produce smoke. It is clean energy.
  3. Fission of one atom of uranium produces 10 million times the energy released by burning of one atom of carbon.
  4. Fusion of four hydrogen atoms produces a huge amount of energy approximately equal to 27 MeV.

In-Chapter Exercise

*Question 1:

Can any source of energy be pollution-free? Why or why not? 

Answer:

No source of energy can be pollution-free. It is considered that solar cells are pollution- free. However, even their making causes environmental damage indirectly.

Also, in the case of nuclear energy, there is no waste produced after the  fusion reactions. However, it is not totally pollution-free. To start the fusion reactions, approximately 107 K temperature is required, which is provided by fission reactions. The wastes released from fission reactions are very hazardous. Hence, no source of energy is pollution-free.

*Question 2:

Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Answer:

Hydrogen gas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon contents. Carbon is a form of pollutant present in CNG. On the other hand, hydrogen is waste-free. The fusion of hydrogen does not produce any waste. Hence, hydrogen is cleaner than CNG.

In-Chapter Exercise

Question 1:

Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Answer:

Two renewable sources of energy are as follows:

  1. Sun: The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium, fusion of helium into other heavy elements, and so on. A large amount of hydrogen and helium is present in the Sun. Therefore, solar energy can replenish on its own. The Sun has 5 billion years more to burn. Hence, solar energy is a renewable source of energy.
  2. Wind: Wind energy is derived from air blowing with high speed. Wind energy is harnessed by windmills in order to generate electricity. Air blows because of uneven heating of the Earth. Since the heating of the Earth will continue forever, wind energy will also be available forever.

Question 2:

Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Answer:

Two exhaustible energy sources are as follows:

  1. Coal: It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non renewable or exhaustible source of energy.
  2. Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the Earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.

Last Exercise

Question 1:

A solar water heater cannot be used to get hot water on

(a) a sunny day (b) a cloudy day

(c) a hot day (d) a windy day 

Answer:

(b) A solar water heater uses solar energy to heat water. It requires bright and intense sunlight to function properly. On a cloudy day, the sunlight reflects back in the sky from the clouds and is unable to reach the ground. Therefore, solar energy is not available for the solar heater to work properly. Hence, solar water heater does not function on a cloudy day.

Question 2:

Which of the following is not an example of a biomass energy source?

(a) wood (b) gobar gas

(c) nuclear energy (d) coal 

Answer:

(c) Biomass is a source of energy that is obtained from plant materials and animal wastes. Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atom is bombarded with low-energy neutrons. Hence, uranium atom splits into two relatively lighter nuclei. This reaction produces huge amount of energy. In nuclear fusion reaction, lighter nuclei are fused together to form a relatively heavier nuclei. This reaction produces tremendous amount of energy. Hence, nuclear energy is not an example of biomass energy source.

Wood is a plant material, gobar gas is formed from animal dung, and coal is a fossil fuel obtained from the buried remains of plants and animals. Hence, these are biomass products.

*Question 3:

Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

  1. Geothermal energy
  2. Wind energy
  3. Nuclear energy
  4. Biomass

Answer:

(c) Nuclear energy is released during nuclear fission and fusion. In nuclear fission, uranium atoms are bombarded with low-energy neutrons. Hence, the uranium atom splits into two relatively lighter nuclei. This reaction produces a huge amount of energy. In nuclear fusion reactions, lighter nuclei are fused together to form a relatively heavier nuclei. The energy required to fuse the lighter nuclei is provided by fission reactions. 

This reaction produces a tremendous amount of energy. These reactions can be carried out in the absence or presence of sunlight. There is no effect of sunlight on these reactions. Hence, nuclear energy is not ultimately derived from the Sun’s energy.

Geothermal energy, wind energy, and biomass are all ultimately derived from solar energy.

Geothermal energy is stored deep inside the earth’s crust in the form of heat energy. The heating is caused by the absorption of atmospheric and oceanic heat. It is the sunlight that heats the atmosphere and oceans.

Wind energy is harnessed from the blowing of winds. The uneven heating of the earth’s surface by the Sun causes wind.

Biomass is derived from dead plants and animal wastes. Chemical changes occur in these dead plants and animal wastes in the presence of water and sunlight. Hence, bio- mass is indirectly related to sunlight.

Question 4:

Compare and contrast fossil fuels and the Sun as direct sources of energy. 

Answer:

Fossil fuels are energy sources, such as coal and petroleum, obtained from underneath the Earth’s crust. They are directly available to human beings for use. Hence, fossil fuels are the direct source of energy. These are limited in amount. These are non-renewable sources of energy because these cannot be replenished in nature. Fossil fuels take millions of years for their formation. If the present fossil fuel of the Earth gets exhausted, its formation will take several years. Fossil fuels are also very costly.

On the other hand, solar energy is a renewable and direct source of energy. The Sun has been shining for several years and will do so for the next five billion years. Solar energy is available free of cost to all in an unlimited amount. It replenishes in the Sun itself.

Question 5:

Compare and contrast biomass and hydroelectricity as sources of energy.

Answer:

Biomass and hydro-electricity both are renewable sources of energy. Biomass is derived from dead plants and animal wastes. Hence, it is naturally replenished. It is the result of natural processes. Wood, gobar gas, etc. are some of the examples of bio- mass.

Hydro-electricity, on the other hand, is obtained from the potential energy stored in water at a height. Energy from it can be produced again and again. It is harnessed from water and obtained from mechanical processes.

Question 6:

What are the limitations of extracting energy from −

(a) the wind? (b) waves? (c) tides? 

Answer:

  1. Wind energy is harnessed by windmills. One of the limitations of extracting energy from wind is that a windmill requires wind of speed more than 15 km/h to generate electricity. Also, a large number of windmills are required, which covers a huge area.
  2. Very strong ocean waves are required in order to extract energy from waves.
  3. Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.

Question 7:

On what basis would you classify energy sources as

  1. renewable and non-renewable?
  2. exhaustible and inexhaustible?

Are the options given in (a) and (b) the same? 

Answer:

(a) The source of energy that replenishes in nature is known as a renewable source of energy. Sun, wind, moving water, biomass, etc. are some of the examples of renewable sources of energy.

The source of energy that does not replenish in nature is known as a non-renewable source of energy. Coal, petroleum, natural gas, etc. are some of the examples of non- renewable sources of energy.

(b) Exhaustible sources are those sources of energy, which will deplete and exhaust after a few hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.

Inexhaustible resources of energy are those sources, which will not exhaust in future. These are unlimited. Biomass is one of the inexhaustible sources of energy.

Yes. The options given in (a) and (b) are the same.

*Question 8:

What are the qualities of an ideal source of energy? 

Answer:

An ideal source of energy must be:

  1. Economical
  2. Easily accessible
  3. Smoke/pollution free
  4. Easy to store and transport
  5. Able to produce huge amount of heat and energy on burning

Question 9:

What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Answer:

Solar cooker uses Sun’s energy to heat and cook food. It is inexhaustible and clean renewable source of energy. It is free for all and available in unlimited amount. Hence, operating a solar cooker is not expensive.

Disadvantage of a solar cooker is that it is very expensive. It does not work without sunlight. Hence, on cloudy day, it becomes useless.

The places where the days are too short or places with cloud covers round the year, have limited utility for solar cooker.

Question 10:

What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Answer:

Industrialization increases the demand for energy. Fossil fuels are easily accessible sources of energy that fulfil this demand. The increased use of fossil fuels has a harsh effect on the environment. Too much exploitation of fossil fuels increases the level of green house gas content in the atmosphere, resulting in global warming and a rise in the sea level.

It is not possible to completely reduce the consumption of fossil fuels. However, some measures can be taken such as using electrical appliances wisely and not wasting electricity. Unnecessary usage of water should be avoided. Public transport system with mass transit must be adopted on a large scale. These small steps may help in reducing the consumption of natural resources and conserving them.

Access Answers for Science NCERT Class 10 Chapter 14- Sources of Energy (All intext and Exercise Questions Solved)

In text Questions Page:243

Q1. What is a good source of energy?

Solution:

A good source of energy has the following properties:

  • Be economical
  • Easy storage and transportation
  • Easy availability
  • Work done per unit volume or mass should be large.

Q2. What is a good fuel?

Solution:

A fuel is said to be good when it is easily available and when it produces a large amount of heat energy when burnt.

Q3. If you could use any source of energy for heating your food, which one would you use and why?

Solution:

For heating and cooking, natural gas can be used for the below given reasons:

  • It is easy to use
  • It is easily available
  • Easy transportation
  • It does not produce huge amount of smoke when burnt
  • It is highly inflammable.

In text Questions Page: 248

Q1. What are the disadvantages of fossil fuels?

Solution:

Following are the disadvantages of fossil fuels:

  • Fossil fuels like coal and petroleum results in air pollution as there is release of huge amount of pollutants.
  • Gases such as carbon dioxide is released when a fossil fuel is burnt, which causes global warming.
  • Soil fertility and potable water is affected by the oxides of carbon, nitrogen, sulphur, etc. that are released from fossil fuels.

Q2. Why are we looking at alternate sources of energy?

Solution:

The reason why we are looking at alternate sources of energy is because the fossil fuels are non-renewable sources of energy, i.e. they are not available in large quantities and cannot be replenished. Fossil fuels will get exhausted if their consumption is not controlled. Therefore, it is better to switch to alternate source of energy.

Q3. How has the traditional use of wind and water energy been modified for our convenience?

Solution:

In olden days, wind energy was trapped used windmills to do mechanical works like lifting or drawing water from a well. But these days, windmills are used to generate electricity. The kinetic energy of wind is trapped and converted into electricity with the help of rotatory motion of the blades, which turns the turbine of the electric generator to produce electricity.

Similarly, waterfalls were the source of potential energy in olden days. But these days as the number of waterfalls has reduced, water dams are constructed and are used as a source to trap the potential energy. Here, the water falls from a certain height on the turbine producing electricity.

In text Questions Page: 253

14.3 ALTERNATE OR NON-CONVENTIONAL SOURCE OF ENERGY

Q1. What kind of mirror – concave, convex or plain would be best suited for use in a solar cooker? Why?

Solution:

For a solar cooker the heat source is sunlight for heating and cooking. The reason why a mirror is used is to reflect and focus the sunlight at one point. So a concave mirror can be used in a solar cooker, as it focuses all the sunlight at one point resulting in increase in temperature, thereby heating and cooking the food.

Q2. What are the limitations of the energy that can be obtained from the ocean?

Solution:

The different forms of energy that can be obtained from the ocean are tidal energy, wave energy and ocean thermal energy. Following are the limitations of the energy obtained from ocean:

  • The relative positioning of the earth, the sun and the moon has an impact on the tidal energy.
  • For the conversion of tidal energy into electricity, high dams are required.
  • To obtain electricity from wave energy, very strong waves are required.
  • For trapping the ocean thermal energy, there should be a temperature difference of more than 20°C between hot surface water and the cold water at a depth.

Q3. What is geothermal energy?

Solution:

Geothermal energy can be defined as the energy that is obtained from the earth. The energy can be obtained from the hot spots that are formed when the molten rocks at the core of the earth are pushed to the earth’s crust. Hot springs are used for the production of electricity in the geothermal power plants.

Q4. What are the advantages of nuclear energy?

Solution:

Following are the advantages of nuclear energy:

  • Amount of energy produced per unit mass is large
  • As it does not produce any pollutants, it is clean
  • Fission of 1 atom of uranium produces 10 million times the energy that is obtained by burning 1 atom of carbon.

14.4. ENVIRONMENTAL CONSEQUENCES

Q1. Can any source of energy be pollution-free? Why or why not?

Solution:

No source of energy can be completely pollution-free. But solar cells are considered to be pollution-free. But their manufacturing may cause environmental damage. In case of nuclear energy, the waste produced after fusion is zero. But the wastes that are produced during fission are hazardous. Hence, no source of energy is pollution-free.

Q2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Solution:

Hydrogen gas is cleaner than CNG as CNG contains hydrocarbons. Carbon is a form of pollutant in CNG. On the other hand, hydrogen is waste-free and the fusion of hydrogen does not produce any waste. Hence, hydrogen as a rocket fuel is cleaner than the CNG.

In text Questions Page: 254

Q1. Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Solution:

Following are the two sources of energy that are renewable:

  • Wind: Wind energy is obtained from the air which is blowing at a high speed. Wind energy is trapped using windmills so as to generate electricity. Blowing of air is dependent on uneven heating of the earth. Since the heating of the earth is forever, wind availability will also be forever.
  • Sun: The energy obtained from the sun is known as solar energy. It is produced by the fusion of hydrogen into helium, fusion of helium into other heavy metals and it continues. A large amount of hydrogen and helium is available in the sun which will never be exhausted. Hence, solar energy is renewable source of energy.

Q2. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Solution:

Following are the two sources of energy that are exhaustible:

  • Wood: The source of wood are forests. Due to deforestation the number of forests are reducing. We know that it takes years to grow forest. If the rate of deforestation increases, the availability of wood will decrease. Hence, wood is an exhaustible source of energy.
  • Coal: The source of coal is from the dead remains of the plants and animals that remained buried for years. Industrialization has increased the demand for coal and it cannot be replenished. Hence, coal is also an exhaustible source of energy.

Exercises Questions Page: 254

Q1. A solar water heater cannot be used to get hot water on
a. A sunny day
b. A cloudy day
c. A hot day
d. A windy day

Solution: b) A cloudy day

A solar water heater uses solar energy to heat water. On a cloudy day, the sunlight won’t be intense and bright enough and it gets reflected back in the sky from the clouds. This holds the sunlight from reaching the ground. Therefore, solar energy won’t be available for the solar water heater to heat the water.

Q2. Which of the following is not an example of a bio-mass energy source?
a. Wood
b. Gobar-gas
c. Nuclear energy
d. Coal

Solution: c) Nuclear energy

Bio-mass is obtained from the dead plants and animal wastes. In these dead plants and animals there is a chemical change as they react with water and sunlight. But nuclear energy is obtained by fusion and fission of atoms resulting in tremendous release of energy. Both nuclear fusion and fission can be carried out in the absence of the sunlight.

Wood is a part of plant, gobar-gas is obtained from the animal dung and coal is obtained by the dead remains of the plants and animals. Therefore, they are all bio-mass energy products.

Q3. Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the sun’s energy?
a. Geothermal energy
b. Wind energy
c. Nuclear energy
d. Bio-mass

Solution: c) Nuclear energy

Nuclear energy is produced by nuclear fusion and nuclear fission. In nuclear fission, uranium atoms are bombarded with low energy neutrons resulting in splitting of the atom into two relatively lighter nuclei. In nuclear fusion, lighter nuclei are fused together to form a relatively heavier nuclei. The energy produced in nuclear reaction is tremendous and can be carried out in the absence of sunlight.

Geothermal energy is obtained from the deep stored energy in the form of heat in the earth’s crust. The uneven heating of the earth’s surface results in wind movement and bio-mass is obtained from the dead remains of the plants and the animals.

Q4. Compare and contrast fossil fuels and the sun as direct sources of energy.

Solution:

Fossil fuels are obtained from the earth’s crust as they are the remains of the dead plants and animals. They are similar to coal and petroleum and readily available for use. These are non-renewable source of energy and cannot be replenished.

Whereas solar energy is abundant in nature and can be replenished.

Q5. Compare and contrast bio-mass and hydroelectricity as sources of energy.

Solution:

Bio-mass is obtained from the dead plants and animals. It is a renewable source of energy. Examples of bio-mass sources of energies are wood, gobar-gas.

Hydroelectricity is obtained from the potential energy of the stored water at a certain height. Water from a certain height is made to fall on the turbines of the generator resulting in electricity. Dams and reservoirs are used in hydroelectricity.

Both bio-mass and hydroelectricity are renewable sources of energies.

Q6. What are the limitations of extracting energy from:
a. The wind?
b. Waves?
c. Tides?

Solution:

  • a) The wind: Wind energy is trapped using windmills. One of the limitations of the wind energy is that the windmills requires a speed more than 15 km/h to generate electricity. And the number of windmills will be more to cover a huge area.
  • b) Waves: In order to extract energy from the waves, very strong ocean waves are needed.
  • c) Tides: In order to extract energy from the tides, the sun, the moon and the earth should be in a straight alignment and the tides should be very strong.

Q7. On what basis would you classify energy sources as:
a. Renewable and non-renewable?
b. Exhaustible and inexhaustible?

Are the options given in (a) and (b) the same?

Solution:
a) Renewable and non-renewable:
Renewable energy sources are those which replenish on their own and are easily available in nature. Like solar energy, tidal energy, wind energy, bio-mass.

Non-renewable energy sources are those which do not replenish on their own and have limited availability in nature. Like fossil fuels which includes petroleum, coal and natural gas.

b) Exhaustible and inexhaustible:
Exhaustible source of energy are those which deplete after few hundred years. Like coal and petroleum.

Inexhaustible source of energy are those which do not deplete and are available in abundant quantity. Like solar and wind energy.

Q8. What are the qualities of an ideal source of energy?

Solution:

Following are the qualities of an ideal source of energy:

  • It should be economical
  • It should be easily available
  • Pollution free
  • Easy transportation and storage
  • The amount of energy produced when burnt should be huge.

Q9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Solution:

Advantages:

The heat source for a solar cooker is sunlight. It is a clean renewable and inexhaustible source of energy. As its availability is unlimited, it will be pocket-friendly.

Disadvantages:

It doesn’t work on a cloudy day.

Q10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Solution:

Industrialization demands for more energy and to fulfil these demands fossil fuels are used as they are readily available. Due to their harsh usage, it has an impact on the environment. Too much exploitation of fossil fuels has led to greenhouse effect resulting in global warming.

But there are few possibilities of reducing this by reducing the usage of fossil fuels and opting for alternate sources of energy. Reduce the unnecessary usage of electricity and water. Opt for public transportation and lessen using own vehicles. These are a few small steps that can be implemented to reduce energy consumption.

NCERT Solutions for Class 10 Science Chapter 14- Sources of Energy

This chapter holds a weightage of 1 mark in the examination. A single question was asked from this chapter in the previous year examination.

This chapter includes the following topics:

14.1 What Is A Good Source Of Energy?

14.2 Conventional Sources Of Energy

14.3. Alternative Or Non-Conventional Sources Of Energy

14.4. Environmental Consequences

14.5 How Long Will An Energy Source Last Us?

List of Exercises

Exercise Solutions 10 Questions (3 MCQs, 3 long, 4 short)

What is a Good Source of Energy?- 4 Questions

Non-Conventional Sources of Energy- 3 Questions

Conventional Sources of Energy- 2 Questions

Environmental Consequences- 1 Question

NCERT Solutions for Class 10 Science Chapter 14- Sources of Energy

Energy is derived from several sources. These sources are classified as:

  • Renewable Sources
  • Non-renewable Sources

Renewable energy is the one that is derived from natural sources such as sun, wind, water, etc and can be replenished. The energy derived from these natural sources can be converted into various forms of energy such as solar energy, which is widely used in solar cookers, solar panels to generate electricity, solar batteries etc., wind energy used in windmills.

Non-renewable energy is obtained from natural resources that once exhausted cannot be replenished. Coal, oil and natural gas are the sources of non-renewable energy. It takes several years for the formation of these resources. These are widely used in today’s scenario. However, they are less eco-friendly when compared to renewable resources as they produce a lot of environmental pollution when burnt.

These sources of energy have several advantages and disadvantages. Therefore, they should be used wisely. The non-renewable sources are on the verge of getting exhausted. Alternative sources of energy are being searched which can be used in an environment-friendly manner without being depleted.

Key Features of NCERT Solutions for Class 10 Science Chapter 14- Sources of Energy

  • NCERT Solutions are the best way to evaluate yourself.
  • It creates a better understanding of the concepts.
  • Created by experts after a lot of research, NCERT Solutions provide accurate information.
  • The sample papers and MCQs are provided for better practice with the questions from previous year question papers.
  • The questions along with the answers are helpful to clarify the doubts.

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The NCERT Solutions for Class 10 Science Chapter 14 are the answers to the questions present in the prescribed textbook. The solutions are created by the subject experts at SWC based on the grasping abilities of students. The faculty provide 100% accurate and quality solutions based on the CBSE guidelines and exam pattern. Each and every solution is explained in a simple language to boost the confidence among students to score well in the board exams.


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NCERT Solutions Class 10 Science Chapters

  • Chapter 1 Chemical Reaction and equation
  • Chapter 2 Acid, Base and Salts
  • Chapter 3 Metals & Non-Metals
  • Chapter 4 Carbon and its Compounds
  • Chapter 5 Periodic Classification of Elements
  • Chapter 6 Life Processes
  • Chapter 7 Control and Coordination
  • Chapter 8 How do Organisms Reproduce
  • Chapter 9 Heridity
  • Chapter 10 Light, Reflection & Refraction
  • Chapter 11 Human Eye
  • Chapter 12 Electricity
  • Chapter 13 Magnetic effects of electric current
  • Chapter 14 Sources of Energy
  • Chapter 15 Environment

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