KSEEB Class 10 Science Important Questions Chapter 14 Sources of Energy

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Karnataka SSLC Class 10 Science Important Chapter 14 Sources of Energy

Question 1.
What is energy?
Answer:
The ability ortne capacity to do work is called energy.

Question 2.
List the various forms of energy.
Answer:
Energy exists in nature in several forms. Some of the forms of energy are heat energy, electrical energy, chemical energy, mechanical energy, light energy, sound energy, etc.

Question 3.
What is the law of conservation of energy ?
Answer:
The law of conservation of energy states that ‘energy is neither created nor destroyed. However, energy in one form can be converted into other forms’.

Question 4.
Name the type of conversion of energy in the following situations:

1. A candle is burning,
2. A plate is dropped from a height,
3. Hot water is kept in a room.

Answer:

1. When a candle bums, chemical energy is converted into heat and light.
2. When a plate is held at a height, it possesses potential energy. When it is dropped, its potential energy is converted into kinetic energy. When the plate hits the ground, its kinetic energy is changed mostly into sound energy.
3. When hot water is kept in a room, the heat contained in water is transferred to the surrounding air molecules and the air molecules move away. Here, heat energy is converted into kinetic energy.

Question 5.
Why is there energy crisis when energy is conserved?
Answer:
Whenever energy is converted from one form to another, energy in usable form usually gets dissipated into the surroundings in less usable forms. It is not easy to recover dissipated energy for our use. Hence, any source of energy we use to do work is consumed and cannot be used again. Therefore, energy crisis occurs.

Question 6.
List the various sources of energy.
Answer:
Sun is the biggest natural source of energy to us. Other sources of energy include fuels, wind, flowing water, heat in the interior of the earth, nuclei of atoms, tides, floods, ocean waves etc.

Question 7.
List four forms of energy that you use from morning, when you wake up, till you reach the school. From where do we get these different forms of energy? Can we call these ‘sources’ of energy? Why or why not?
Answer:

1. We use light early in the morning for studying. Light is a form of energy. We get light by converting electrical energy into light. Light is not a source of energy but is only a form of energy.
2. We use electrical energy for heating water for bathing. Electricity is not a source of energy. It is only a form of energy.
3. We take breakfast. Food is a form of chemical energy. Chemical energy stored in food comes from the sun. Therefore, chemical energy is not a source of energy.
4. We use one or the other vehicle to reach school. We use fuels to run the vehicles. Fuels have chemical energy. Chemical energy is only a form of energy and not a source of energy.

Question 8.
What are the qualities of an ideal source of energy?

OR

What is a good source of energy?
Answer:
A good source of energy is one:

1. Which would do a large amount of work per unit volume or mass
2. Is easily accessible
3. Is easy to store and transport
4. Is economical.

Question 9.
What is a fuel? Give examples.
Answer:
Any combustible substance that burns in air producing heat is called a fuel.
E.g.: Petrol, diesel, LPG, hydrogen, firewood, coal, charcoal, CNG, biogas, kerosene, etc.

Question 10.
What is a good fuel?
Answer:
A good fuel has the following characteristics:

1. It should be easily available at a cheaper cost.
2. It should not give any toxic products or smoke on burning.
3. It should be a clean fuel. It should not leave behind substances like ash on burning.
4. It should have high calorific value.
5. It should burn at a moderate rate.
6. It should be easily storable and transportable.

Question 11.
If you could use any source of energy for heating vour food, which one would you use and why?
Answer:
Natural gas can be used for heating and cooking food. This is because natural gas is a clean fuel with high calorific value. It does not produce smoke on burning. It is easy to use and easy to transport.

Question 12.
How are energy sources classified? Give examples for each type.
Answer:
Energy sources are broadly classified into two types as

• Renewable sources of energy and
• Non-renewable sources of energy.

Examples of non-renewable sources of energy: Petrol, coal, petroleum gas etc.
Examples of renewable sources of energy: Wind, water, tides, sun etc.

Question 13.
What are renewable sources of energy? Give two examples.
Answer:
Sources of energy that are replenished by natural processes within a reasonable period of time and hence are available for continuous use are known as renewable sources of energy.
E.g.: Wind energy, hydel energy etc.

Question 14.
What are non-renewable sources of energy? Give two examples.
Answer:
Sources of energy that do not get replenished by natural cycles within a reasonable period of time and hence get exhausted with continuous use are known as non-renewable sources of energy.
E.g.: Petroleum, coal etc.

Question 15.
What are conventional sources of energy? Give examples.
Answer:
Non-renewable sources of energy, which we have been using since a long time, are known as conventional sources of energy.
E.g.: Coal, petroleum and natural gas.

Question 16.
Make a list of the advantages of non-conventional sources of energy over conventional sources of energy.
Answer:
Non-conventional sources of energy are available in great abundance. They are renewable sources of energy. They do not cause environmental pollution. They are available in both urban and rural areas including remote areas. Finally, non-conventional sources of energy are eco-friendly.

Question 17.
What are non-conventional sources of energy ? Give examples.
Answer:
Those sources of energy which are available on earth and serve as alternatives to conventional sources of energy, are known as non-conventional sources of energy.
E.g.: Solar energy, wind energy, geothermal energy, nuclear energy, hydel energy, tidal energy, wave energy, bio-mass etc.

Question 18.
Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing of one non-conventional source of energy.
Answer:
Conventional sources of energy include coal, petroleum, natural gas, firewood, dried dung, agricultural wastes etc. Non-conventional sources of energy include bio-energy, wind energy, geothermal energy, solar energy, tidal energy, wave energy, etc.

Harnessing solar energy: Solar energy is a non-conventional source of energy. It is available in great abundance. Solar energy is used directly as heat or by converting it directly into electricity. Devices such as solar cooker, solar water heater, solar panel and solar furnaces make use of the radiant heat of the sun.

Solar cells convert sun’s energy directly into electrical energy. Solar energy is used indirectly when we harness the energy of the biomass, wind, sea waves, tides, biogas plants, windmills, and ocean thermal energy.

Question 19.
What are the various sources of energy which people have been using to meet their needs?
Answer:
People have been using coal, petroleum, natural gas, nuclear energy, hydel energy, wind energy and a few other sources to meet their energy requirements.

Question 20.
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:
1. Energy sources are classified as renewable and non-renewable on the basis of whether or not they get replenished through natural cycles. The sources of energy such as biomass, hydel energy etc., which get replenished by natural processes are known as renewable sources of energy. Biomass, sun, wind etc., are some examples of renewable sources of energy.

The sources of energy such as coal and petroleum, which do not get replenished in nature, are known as non-renewable sources of energy. Coal, petroleum etc., are some examples of non-renewable sources of energy.

2. Energy sources are classified as exhaustible and inexhaustible sources on the basis of whether the sources get depleted with continuous use and get exhausted at a future date.

Exhaustible sources are those sources of energy, which will get exhausted or disappear after some time. Inexhaustible sources of energy are those sources which will not get depleted with continuous use.

Question 21.
List the limitations of conventional sources of energy.
Answer:
Our conventional sources of energy such as coal, petroleum and natural gas have the following limitations:

1. They are fast depleting and they are non-renewable sources of energy.
2. They cause pollution of the environment and hence are not eco-friendly.
3. The new deposits of these energy sources have become far and few.

Question 22.
What are fossil fuels? Give examples.
Answer:
Fuels formed over millions of years in the interior of the earth from ancient remains of plants and animals are called fossil fuels.
E.g.: Coal, petroleum and natural gas.

Question 23.
What are the disadvantages of fossil fuels?
Answer:
The following are some of the disadvantages of fossil fuels:
1. Fossil fuels are non-renewable sources of energy. This means that there is a finite amount of fossil fuels available and the reserves are not replenished through natural cycles. Therefore, they get exhausted with continuous use.

2. Burning of fossil fuels contributes to global warming as they release carbon dioxide to the earth’s atmosphere.

3. Use of fossil fuels is unsustainable. We are spending our fossil fuel reserves in a manner that very soon we will not get enough fossil fuels to operate our machines and vehicles.

4. Use of fossil fuels causes atmospheric pollution leading to many environmental and health hazards.

Question 24.
What are the environmental consequences of using fossil fuels?
Answer:
Use of fossil fuels raises many environmental concerns. Burning of fossil fuels releases carbon dioxide, which is the major greenhouse gas in our atmosphere. They also release oxides of sulphur and nitrogen, which may lead to acid rain.

Incomplete burning of fossil fuels in engines produces carbon monoxide, particulate matter and smoke which causes many environmental problems. Disposing of coal ash is a major problem. Fossil fuels affect not only living beings but also affect our heritage. They have detrimental effect on the climate.

Question 25.
How can we reduce the pollution caused by fossil fuels?
Answer:
The following steps may be taken to reduce pollution caused by fossil fuels:

1. The pollution caused by burning fossil fuels can be reduced by increasing the efficiency of the combustion process and using various techniques to produce smokeless appliances.
2. The air pollution caused by burning of coal or petroleum products can be reduced by afforestation.
3. We must reduce the use of fossil fuels wherever possible and conserve these fuels.
4. We must adopt technologies that use alternative sources of energy, which are friendlier to the environment.

Question 26.
What are thermal power plants? How do they produce electricity?
Answer:
A power generating station in which heat energy produced by burning of a fuel is converted to electric power is called a thermal power plant.

Fossil fuels are burnt in power stations to heat up water to produce steam. The steam so produced is used to run the turbine, which is connected to a generator. The generator converts the mechanical energy of the turbine into electrical energy.

Question 27.
Why are thermal power plants set up near coal or oil fields?
Answer:
The transmission of electricity is more efficient than transporting coal or petroleum over the same distance. Therefore, many thermal power plants are set up near coal or oil fields.

Question 28.
What is hydel power? How do hydel power stations produce electricity?
Answer:
Electric power generated by the conversion of the stored energy of free-falling water into electrical energy is called hydel power or hydroelectric power.

In order to produce hydel electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs. The water level rises and in this process the kinetic energy of flowing water gets transformed into potential energy.

The water from the high level in the dam is carried through pipes, to the turbine, installed at the bottom of the dam. The energy of water rotates the turbine, which in turn operates a generator. The generator converts the mechanical energy of the turbine into electrical energy.

Question 29.
Why is hydel power considered a renewable source of energy?
Answer:
The water in the reservoir would be refilled each time it rains. Therefore, we need not have to worry about hydroelectricity sources getting used up the way fossil fuels would. Therefore, hydel energy is a renewable source of energy.

Question 30.
How is the construction of dams across rivers linked with the production of greenhouse gases?
Answer:
The vegetation that submerged due to construction of dams, rots in anaerobic condition and gives out large amount of methane (CH₄) in nature which is a greenhouse gas.

Question 34.
What are the problems associated with construction of big dams?
Answer:
There are many problems associated with the construction of big dams. Dams in general and big dams in particular can be constructed only in a limited number of places, especially in regions covered by hilly terrains. Big dams submerge large areas of agricultural land and human habitation causing economic loss and displacement of people.

Big dams cause destruction of habitats, disrupt ecological balance in the region. The submerged vegetation rots under anaerobic conditions and gives rise to large amounts of methane, which is also a greenhouse gas. The problem of rehabilitating the displaced people is a huge challenge associated with the construction of big dams.

Question 32.
What is biomass? Make a list of some of the sources of biomass.
Answer:
Any biological material obtained from living or recently lived organisms is called biomass.
Some of the sources of biomass include dead and decaying plants and animals, dung of animals, agricultural crop residues, forest residues, fallen leaves of plants, municipal solid waste, sewage, and vegetable peels.

Question 33.
Name some fuels obtained from biomass.
Answer:
Fuels obtained from biomass include firewood, crop residue, biogas, charcoal, etc.

Question 34.
What is biomass energy? Give examples of biomass fuels.
Answer:
Energy obtained from biomass materials in the form of fuels or electricity is called biomass energy. Biomass fuels include firewood, cow dung cake, charcoal etc.

Question 35.
What can he done to obtain bio-energy using biomass?
Answer:
Biomass appears in several forms. The method of harnessing energy from each one of them could be different. Direct burning of these materials generally causes pollution but could be the cheapest form of energy. For example, using wood or dried cow dung cakes as fuel generates a lot of smoke. However, if cow dung is used in biogas plant, clean fuel can be generated.

In villages, all types of biomass are traditionally burnt directly to produce heat. And if modern methods are used, they can be utilized properly. A number of transportation fuels can be produced from biomass, helping to alleviate demand for petroleum products and improve the greenhouse gas emissions. Ethanol and biodiesel are examples of such bio-fuels.

Question 36.
Why is biomass energy considered a renewable source of energy?
Answer:
Biomass is organic matter that can be quickly replenished unlike coal. Biomass is considered a renewable energy source because its inherent energy comes from the sun and it can be replenished in a relatively short time.

Question 36.
List the advantages of biomass energy.
Answer:
The following are some of the advantages of biomass energy :

1. It is a renewable source of energy.
2. It is less polluting compared to fossil fuels. While producing biomass energy, we recycle . wastes, which reduces pollution and the spread of diseases.
3. It can be generated from everyday human and animal wastes, vegetable and agriculture leftovers etc. Therefore, biomass energy helps in cleanliness in villages and cities.
4. It provides manure for agriculture and gardens.
5. Biomass energy is relatively cheaper and reliable.

Question 38.
List the disadvantages of biomass energy.
Answer:
The following are some of the disadvantages of biomass energy:

1. Continuous supply of biomass is required to generate biomass energy.
2. Cost of construction of biogas plant is high.
3. Biogas plant requires space and produces dirty smell.
4. Some of the biomass fuels do not produce much heat on burning.
5. Some biomass fuels produce lot of smoke when they are burnt.

Question 39.
What is biogas? Explain the principle and working of a biogas plant with a labelled schemati diagram.

OR

Explain the structure of a biogas plant and the process of production of fuel in biogas plant.

OR

Draw the schematic diagram of gobar gas plant Label the following parts:

1. Slurry,
2. Gas outlet.

Answer:

A gaseous fuel consisting of a mixture of different gases with methane being its largest constituent and produced by the breakdown of organic matter in the absence of oxygen is called biogas.

A biogas plant has a dome-like structure built with bricks. Slurry of cow-dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which there is no oxygen. Anaerobic micro-organisms decompose complex compounds of the slurry.

This breakdown takes a few days. During breakdown, gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are released. This mixture of gases is called biogas. The biogas is stored in the gas tank above the digester from which they are drawn through pipes for heating or lighting.

Question 40.
What is slurry?
Answer:
A semi-fluid mixture prepared by mixing cow dung and other organic materials with water is called slurry. It is the starting material for the production of biogas in a biogas plant.

Question 41.
Why is slurry left behind in bio-gas plants considered useful?
Answer:
Slurry left behind in biogas plants is used as a manure as it is rich in nitrogenous compounds.

Question 42.
Name the major constituent of biogas.
Answer:
The chief constituent of biogas is methane.

Question 43.
State the advantages of biogas.

OR

Write the properties of biogas that make it a good fuel.
Answer:
The following are some of the principal advantages of biogas:

1. Bio-gas is an excellent fuel as it contains up to 75% methane.
2. It burns without smoke, leaves no residue like ash.
3. Its heating capacity is high. This means, biogas has high calorific value.
4. Bio-gas can be used for both heating and lighting.
5. The slurry left behind is good manure, rich in nitrogen and phosphorus.
6. Production of biogas from bio-waste and sewage material provides a safe and efficient method of waste-disposal.

Question 44.
What is wind energy? Why is it considered an indirect form of solar energy?
Answer:
The kinetic energy possessed by moving air is called wind energy. The uneven heating of the atmospheric air causes the movement of air on earth by the heat of the sun. Hence wind energy is an indirect form of solar energy.

Question 45.
What is a windmill? What are its uses?
Answer:
A structure that has parts that are turned around by the wind and used to get certain work done is called a windmill. Windmills can be used to lift water from wells, generate electricity, grind corn etc.

Question 46.
What type of energy conversion occurs in windmills?
Answer:
A windmill converts the kinetic energy of the wind into mechanical or electrical energy.

Question 47.
What are wind turbines used for?
Answer:
Wind turbines are used to harness wind energy for the production of electricity.

Question 48.
What should be the range of speed of wind for setting up of windmills?
Answer:
Windmills can be set up in places where wind speed is higher than 15 km/h.

Question 49.
What are the limitations in obtaining energy from wind?
Answer:
Limitations of wind energy include the following:

1. The wind speed should be higher than 15 Km/h to maintain the required speed of the turbine.
2. Wind energy farms can be established only at those places where wind blows for the greater part of the year.
3. A large area of land is required for establishing wind energy farms.
4. The initial cost of establishing wind energy farms is quite high.

Question 50.
How has the traditional use of wind and water energy been modified for our convenience?
Answer:
Traditional use of wind and water energy has been modified in the following ways:
1. Water energy:
Traditionally, waterfalls were used as a source of potential energy in which water was allowed to fall on the blades of the turbine to produce electrical energy. But waterfalls are fewer in number and therefore dams have been constructed. Now-a-days, hydroelectric power stations produce electricity by harnessing the potential energy of stored water.

2. Wind energy:
Earlier, the windmills were used to harness wind energy to do mechanical work such as lifting or drawing water from a well. But, now-a-days windmills are used to generate electricity. In windmills the rotatory motion of the blades turns the blades: of the turbine to generate electricity.

Question 51.
Why are we looking at alternative sources of energy?
Answer:
Our conventional energy sources are depleting very fast. But, the demand for energy is increasing. Therefore, there is an urgent need to explore alternatives to fossil fuels.

Our conventional sources of energy are highly polluting. Therefore we need to find alternatives that cause lesser pollution and damage to our environment. Conventional energy sources are non-renewable. There is a need to find energy sources that are renewable.

Question 52.
Why is there a need for harnessing non-conventional sources of energy?
Answer:
There is a need for harnessing non-conventional sources of energy for the following reasons:

1. The demand for energy is increasing day by day to meet the basic requirements of our changed life-styles, growing use of machines, and industrialisation in order to improve our living standard.
2. The fossil fuels are non-renewable sources of energy and were formed over millions of years and there are only limited reserves of fossil fuels.

Question 53.
What is solar energy? Why is the sun considered an inexhaustible source of energy?
Answer:
The radiant energy emitted by the sun in the form of heat and light is called solar energy. The availability of solar energy does not depend on the rate at which we use it. It does not get depleted if we use the energy of the sun more and more. This is why sun is considered an inexhaustible source of energy.

Question 54.
What is the source of energy of the sun?
Answer:
The enormous amount of energy of sun is due to nuclear fusion reactions taking place in the interior of the sun. Such reactions are also known as thermonuclear reactions.

Question 55.
How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
Answer:
There are three major ways of harnessing solar energy:

1. Collecting and converting radiant energy into heat energy using solar collectors.
2. Conversion of radiant energy into electrical energy using solar cells.
3. The natural conversion of solar energy into biomass, which in turn serves as a source of energy.

Solar energy has several limitations. The devices to harness solar energy cannot be used at night. Many gadgets do not work well on cloudy days. They cannot provide enough intensity to be used in our daily routine.

These limitations can be overcome by making devices that use low intensity of solar energy and give high intensity of light. We can also store energy in storage batteries and use it during night.

Question 56.
What is a solar cooker?
Answer:
Devices that use solar energy to cook food are called solar cookers.

Question 57.
Name two devices that work using heat energy of the sun.
Answer:
Two of the devices that use solar energy are solar cooker and solar cell.

Question 58.
With the help of a neat, labelled diagram, explain the construction and working of a box type solar cooker.
Answer:

A box type cooker consists of a tray, which is called as cooking tray. It is usually covered with a double glass window. It is kept in a metal or fibreglass outer casing and the space between the cooking tray and outer casing is filled with glass wool or thermocol insulation. The cooking tray has a lid, which contains a plane mirror on its inner surface.

The incoming solar radiation passes directly through the double glass lid and it strikes the blackened cooking pots and the cooking tray. The plane mirror also directs the sun’s radiation into the box. The glass cover transmits short wavelength radiations and is almost opaque to low temperature radiation emitted within the box.

The glass plate creates green house effect inside the box causing the temperature inside to rise. The cooking tray is insulated on the sides and bottom. The cooking containers (with cover) are generally made of aluminium or stainless steel. The cooking vessels placed in the cooking tray are also painted black on the outer surface so that they also absorb solar radiation directly.

Question 59.
What kind of mirror – concave, convex or plain – would be best suited for use in a solar cooker? Why?
Answer:
The type of mirror used in a solar cooker depends on the type of solar cooker. A concave mirror would be best suited for use in a solar cooker designed to create higher temperatures. A concave mirror reflects and focuses the sunlight at a point.

The temperature at that point increases, which heats and cooks the food, placed at that point. However, a plane mirror is suitable for a box type solar cooker because it reflects all the light falling on it to the desired place.

Question 60.
Which part of the solar cooker is responsible for greenhouse effect?
Answer:
Glass sheet present in the solar cooker is responsible for greenhouse effect.

Question 61.
What is the role of a plane mirror and a glass sheet in a solar cooker?
Answer:
1. Plane mirror:
The plane mirror in a box type solar cooker directs the sun’s rays into the box and thus facilitates cooking.

2. Glass sheet:
The glass sheet is used to cover the box. It allows sun’s rays to enter into the box but does not allow it to escape. Thus, it traps sun’s heat inside by creating glass house effect. The heat trapped is absorbed inside the box.

Question 62.
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Answer:
Advantages of using solar cooker:

1. Use of solar cookers does not require any fuel such as cooking gas or kerosene, electricity, coal or wood.
2. Solar cookers work on solar energy, which are available for free.
3. Food cooked in solar cooker is nutritious, as useful nutrients present in food are not denatured because of overheating.
4. Solar cookers are environment-friendly and are safe to use. Solar cookers do not cause any pollution.

Disadvantages of using solar cooker:

1. Solar cookers cannot be used in all places, at all times and in all seasons. They can be used only during daytime when the sun is shining brightly.
2. Solar cookers will take longer time to cook food than conventional cooking methods. Cooking is slow.
3. The mirror requires continuous readjustment to direct the sunlight into the box.

Solar cookers are not suitable to be used in Polar regions. They cannot be used during night times. They are not so suitable where nights are longer than days.

Question 63.
What is a solar cell? What is the principle on which it works?
Answer:
A device that converts solar energy into electrical energy is called a solar cell. A solar cell works on the principle of photovoltaic effect. Photovoltaic effect generates a voltage or an electric current in a material upon exposure to light.

Question 64.
Write the advantages of solar cells.
Answer:
The principal advantages associated with solar cells are that

1. They have no moving parts,
2. They require little maintenance and
3. Work quite satisfactorily without a focusing device.

Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.

Question 65.
What is the range of voltage developed in a typical solar cell? Where are solar cells commonly used?
Answer:
A typical solar cell develops a voltage of 0.5 – 1 V and can produce about 0.7 W of electricity when exposed to the bright Sun. Solar cells are commonly used in traffic signals, for lighting homes, for pumping water etc.

Question 66.
Where are solar cells commonly used?
Answer:
Solar cells are used in many scientific and technological applications. Artificial satellites and space probes use solar cells as the main source of energy. Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels. Traffic signals, calculators and many toys are fitted with solar cells.

Question 67.
What are solar panels? How do they work?
Answer:
A solar panel is an assembly of solar cells that can convert light directly into electricity. Solar panels actually comprise many smaller units called photovoltaic cells connected in series. Each such cell converts sunlight into electricity. Many cells linked together make up a solar panel. The voltage developed in these cells of the panel gets added up and delivers enough electricity for practical use.

Question 68.
Why are solar cells not so popular for common use? Explain.
Answer:
Solar cells are highly expensive. Silicon, which is used for making solar cells, is abundant in nature but availability of special grade silicon for making solar cells is limited.

The entire process of manufacture is still very expensive; silver used for interconnection of the cells in the panel further adds to the cost. This is why solar cells are not so popular for common use.

Question 69.
Compare and contrast fossil fuels and the Sun as direct sources of enerev.
Answer:

Fossil fuels	Energy from the Sun
1. These are exhaustible sources of energy.	Energy from the Sun is inexhaustible.
2. Exploitation of fossil fuels causes environmental pollution and health hazards.	Harnessing solar energy does not pose any environmental issues and does not cause health hazards.
3. Fossil fuels take millions of years for their formation.	Solar energy is readily available and is a direct source of energy.
4. Fossil fuels can be used in all places, in all seasons and at all times.	Solar energy requires the presence of the sun. Thus, solar energy is not available all the time and in all the places.
5. Fossil fuels are costly.	Solar energy is completely free.

Question 70.
How can enegy be harnessed from the sea in different ways?
Answer:
The energy from the sea can be harnessed in different forms, which are as follows:
1. Tidal energy:
Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

2. Wave energy:
A wide variety of devices have been developed and employed to trap huge waves near the seashore for rotation of turbine and production of electricity.

3. Ocean thermal energy:
The sun heats the water at the surface of the sea or ocean, while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean thermal energy conversion plants.

Question 71.
What are tides? How are they caused?
Answer:
The periodic rising and falling of water in the oceans is called tides. Tides are caused by the gravitational interaction between the Earth and the Moon.

Question 72.
What is tidal energy? How is electricity produced from tidal energy?
Answer:
Tidal energy is energy produced from tides. It is a renewable form of energy that converts the natural rise and fall of the tides into electricity.

Question 73.
What is wave energy? How are ocean waves caused?
Answer:
The energy possessed by the waves in oceans and seas is called wave energy. The waves in oceans and seas are caused by the wind. Uneven heating of the air by the heat of the sun produces wind. Wind blowing over the oceans and seas causes rise and fall of waves.

The mechanical energy (both potential and kinetic energy) possessed by the waves is the ocean energy. Wave energy, also known as ocean wave energy, is a type of ocean-based renewable energy source that uses the power of the waves to generate electricity.

Question 74.
How is electricity produced by using energy of the ocean waves?
Answer:
A wide variety of devices have been developed and used to trap wave energy. These devices are installed on the shoreline, near the shore or offshore. They collect the wave energy and use them to rotate turbines and produce electricity.

Question 75.
List the advantages of wave energy.
Answer:
The following are some of the advantages of wave energy:

1. It is an abundant and renewable energy resource as the waves are generated by the wind.
2. Wave energy is practically pollution-free.
3. Wave energy is relatively consistent and predictable as waves can be accurately forecast several days in advance.

Question 76.
Why are wave energy systems more reliable than wind energy systems?
Answer:
Fluctuations in wind speed are very high. Therefore, wind energy systems are less reliable. However, the variations in waves are less pronounced. Hence, wave energy systems are more reliable.

Question 77.
What is ocean thermal energy? List two advantages and two disadvantages of ocean thermal energy.
Answer:
The sun heats the water at the surface of the sea or ocean, while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy and is known as ocean thermal energy. Thus, ocean thermal energy is due to temperature difference at different levels in the ocean.
The advantages of ocean thermal energy are:

• Power is continuous, renewable and pollution-free.
• Power shows very little daily or seasonal variation.

The disadvantages of ocean thermal energy are:

• Ocean thermal energy conversion plants can operate only if the temperature difference between the water at the surface and water at depths up to 2 kms is 20°C or more.
• Efficient commercial exploitation is difficult.

Question 78.
What is the device used to harness ocean energy? Explain the process.
Answer:
Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by using the temperature difference between deep cold ocean water and warm tropical surface water. In such a conversion plant, the warm surface water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of the generator. The cold water from the depths of the ocean is used to condense vapour again to liquid.

Question 79.
Write two different ways of harnessing energy from oceans.
Answer:
Energy can be harnessed from oceans in the following ways:
1. Tidal energy:
Due to the gravitational pull mainly of the moon on the spinning earth, the level of water in the sea rises and falls, called high and low tides. This can be harnessed by constructing a dam across a narrow opening to the sea.

2. Ocean thermal energy:
The sun heats the water at the surface of the sea or ocean, while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean thermal energy conversion plants.

Question 80.
What is geothermal energy? How is electricity produced from geothermal energy?
Answer:
Naturally occurring heat energy found in the interior of the earth’s crust is known as geothcfwial energy. This is one source of energy that is not due to the sun either directly or indirectly.

The steam trapped in rocks is routed through a pipe to a turbine. The turbine begins to rotate which in turn runs a generator and produces electricity.

Question 81.
Write a brief note on geothermal energy.
Answer:
The thermal energy (heat energy) contained in the interior of the earth is known as geothermal energy. There are regions inside the earth where the matter is present in molten state due to the high temperature that prevails there.

This is an inexhaustible source of energy. This is one source of energy which is not due to the sun. The rocks in the interior of the earth’s crust become very hot due to the high temperature below. The underground water that flows over the hot rocks gets heated and turns into steam.

Sometimes the hot water along with steam gushes out from the earth’s surface to form natural geysers. The heat in the interior of the earth can also be harnessed to produce electricity.

Question 82.
What are hot springs?
Answer:
A natural spring of hot water, usually hotter than that of the surrounding region, is called a hot spring.

Question 83.
What are the limitations of the enerev that can be obtained from the oceans?
Answer:
Energy can be obtained from oceans by harnessing tidal energy, wave energy or ocean thermal energy. Each of these has its limitations:
1. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. Such sites suitable for constructing dams are very few. Secondly, the power generation is intermittent and not very large.

2. Waves are generated by strong winds blowing across the sea. Wave energy becomes a viable proposition only where waves are very strong. We do not get strong waves consistently in any given region. Therefore, power output varies and the presently available technologies for harnessing this energy are very expensive.

3. The conversion efficiency in harnessing ocean thermal energy is low (3% – 4%) and a lot of capital investment is required. Therefore, efficient commercial exploitation of this resource is difficult.

Question 84.
What is nuclear energy?
Answer:
Energy in the nuclei of atoms is called nuclear energy. It is the energy released during nuclear fission or fusion, especially when used to generate electricity.

Question 85.
Which is the process used to harness nuclear energy these days? Explain it briefly.
Answer:
A process called controlled chain reaction of nuclear fission harnesses nuclear energy. During fission, a heavy nucleus such as Uranium-235 is bombarded with a slow moving neutron. This splits U-235 into more or less two equal halves producing huge amount of energy.

Question 86.
What is the source of energy produced during nuclear reactions?
Answer:
During nuclear reactions, a small amount of mass is converted into energy in accordance with the formula E = mc². Since mass-energy is conserved in such reactions, huge amount of energy is released.

Question 87.
How is electricity produced from nuclear energy?
Answer:
Nuclear power is derived from energy that is released when relatively large nuclei are split in a series of controlled nuclear reactions. The process of splitting an atom is known as nuclear fission. The resulting heat from fission reactions is used to boil water and to produce steam. The steam drives a steam turbine to generate electricity.

Question 88.
What are the advantages of nuclear energy?
Answer:
Some advantages of nuclear energy include the following:

1. Nuclear energy systems consume very little fuel. Once loaded, a nuclear reactor operates for years together.
2. If maintained and operated properly, nuclear energy systems produce almost no air pollution.
3. Splitting nuclei of atoms releases huge amount of energy per unit mass that is far in excess of the amount of energy produced by any other method.

Question 89.
What are the limitations of nuclear energy?

OR

Write any two hazards of nuclear power generation.
Answer:
The following are some of the limitations of nuclear energy:

1. Nuclear power generation is fraught with hazards of handling radioactive materials at various stages. Mining, storage, and disposal of spent fuels result in environmental contamination by radiation.
2. The cost of installation of a nuclear power plant is quite high.
3. Limited availability of fissionable materials such as uranium is also a problem.
4. There is the risk of accidental leakage of nuclear radiation.
5. The cost of cleaning up the environment in the event of accidental leakage or accidents is enormously high.

Question 90.
“We cannot establish nuclear power reactors everywhere though large amount of electricity is produced by nuclear energy”. Why? Explain.
Answer:
The nuclear power reactors have certain hazards. The major hazard of nuclear power generation is the storage and disposal of spent or used fuels and the uranium continuously decaying into harmful subatomic particles (radiations).

Improper nuclear waste storage and disposal result in environmental contamination. Further, there is the risk of accidental leakage of nuclear radiation. The high cost of installation of a nuclear power plant, high risk of environmental contamination and limited availability of uranium makes large-scale use of nuclear energy prohibitive.

Question 91.
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer:
Two renewable sources of energy are the Sun and the wind.
1. Sun:
The energy derived from the Sun is known as solar energy. Solar energy is produced by the fusion of hydrogen into helium. The sun has enough hydrogen to last for another five billion years. Secondly, solar energy does not get depleted with continuous use. Therefore Sun is a renewable source of energy.

2. Wind:
Wind energy is derived from fast moving air. Air moves because of uneven heating of the Earth by the energy of the Sun. Since the heating of the Earth will continue forever, the wind energy will also be available forever. Therefore, wind is a renewable source of energy.

Question 92.
Can any source of energy be pollution-free? Why or why not?
Answer:
No source of energy can be really pollution-free. The use of any source of energy disturbs the environment in one way or the other. A source of energy like a solar cell is pollution-free in actual operation but the assembly of the device might have caused some damage to the environment. So, in the absolute sense, no source of energy can be called pollution-free.

Question 93.
Hydrogen has been used as a rocket fuel Would you consider it a cleaner fuel than CNG? Why or why not?
Answer:
Hydrogen is a cleaner fuel than CNG. This is because hydrogen produces water on burning whereas CNG on burning produces carbon dioxide. The increase in concentration of carbon dioxide in the atmosphere increases the temperature of the atmosphere leading to global warming. This problem wouldn’t be there if hydrogen is used as fuel.

Question 94.
Suggest steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.
Answer:
Following steps are suggested to minimise the pollution caused by various sources of energy:

1. Avoid misuse and unnecessary use of energy.
2. Use less-polluting sources of energy wherever possible.
3. Use machines that are less polluting and more efficient.

Question 95.
Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Answer:
Yes. It is true that energy from most of our sources is derived from the Sun either directly or indirectly.

Sun is the ultimate source of fossil fuels as they are formed from ancient plants and animals whose life depended on the sun. Wind is created due to the uneven heating of the earth by the sun. The sun maintains the water cycle.

Biomass is created when plants trap sun’s light and convert it into chemical energy. Wave energy and ocean thermal energy are also due to the sun. Therefore, we can say that most of the sources of energy are due to the sun.

Question 96.
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choice.
Answer:
Two of the energy sources that are exhaustible are coal and petroleum. Coal and petroleum are formed in the earth’s crust over millions of years from ancient plants and animal remains. Therefore, they do not get replenished within a reasonable period of time. Hence, they get exhausted with continuous use and rapid exploitation.

Question 97.
Compare and contrast biomass and hydro electricity as sources of energy.
Answer:
Both biomass and hydro electricity are renewable sources of energy. Both of them get replenished through natural processes. Both these sources come to us indirectly from the sun. Biomass comes from living sources whereas hydro electricity comes from non-living sources.

Question 98.
What are the limitations to extracting energy from

1. The wind,
2. Waves, and
3. Tides?

Answer:
Limitations to extracting energy from wind, waves and tides are:

1. A windmill requires winds of speed more than 15 km/h to rotate the turbines and to generate electricity. Secondly, a large number of windmills are required to get feasible output of electric power and large area of land is required to set up so many windmills.

2. Very strong ocean waves are required in order to extract energy from waves. Such strong ocean waves are however not available all the time.

3. Very high tides are required in order to extract energy from tides. However, tides depend on the relative positions of the sun, the moon, and the earth.

Question 99.
What are the environmental consequences of the increasing demand for energy?
Answer:
The following are some of the environmental consequences of increasing demand for energy:
1. Increasing demand for energy leads to excessive use of conventional sources of energy, which are limited in nature. Thus energy crisis may be caused in the future.

2. Exploiting any source of energy disturbs the environment in one or more ways. For example, burning of fossil fuels causes air pollution, acid rain, global warming and climatic changes.

3. In some cases, the actual operation of a device like the solar cell is pollution-free. However, the assembly of the device has the potential to cause some environmental damage.

4. Some renewable energy systems actually create environmental problems as they consume vast areas of land for the exploitation of that resource for our energy needs.

Question 100.
What steps would you suggest to reduce enerev consumption?
Answer:
Following steps can be suggested to reduce energy consumption:

1. Avoiding the misuse and unnecessary use of energy.
2. Maintaining machines in good condition and replacing obsolete technologies with modern
   energy-saving technologies.
3. Using renewable sources of energy to the extent possible and wherever possible.
4. Exploiting natural light, wind and sunlight for domestic purposes in order to reduce the demand for electricity.

Fill In The Blanks

1. The most common greenhouse gas in our atmosphere is carbon dioxide
2. The principle involved in the conversion of solar energy into electrical energy is photovoltaic effect
3. The reaction responsible for the energy of the sun is nuclear fusion
4. The best environment-friendly fuel among coal, firewood, kerosene and biogas is biogas
5. The S.I. unit of calorific value of a fuel is joule per kilogram

Multiple Choice Questions

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 cloudy day

Question 2.
Most of the sources of energy that 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 and biomass
(C) Fossil fuels and wind energy
(D) Tidal energy and wave energy
Answer:
(A) Geothermal energy

Question 3.
Which of the following is a non-renewable source of energy?
(A) Wood
(B) Sun
(C) Fossil fuels
(D) Wind
Answer:
(C) Fossil fuels

Question 4.
Acid rain happens because
(A) sun leads to heating of upper layer of atmosphere
(B) burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere
(C) electrical charges are produced due to friction amongst clouds
(D) earth’s atmosphere contains acids
Answer:
(B) burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere

Question 5.
Fuel commonly used in thermal power plants is
(A) water
(B) uranium
(C) biomass
(D) fossil fuels
Answer:
(D) fossil fuels

Question 6.
In a hydro power plant
(A) potential energy possessed by stored water is converted into electricity
(B) kinetic energy possessed by stored water is converted into potential energy
(C) electricity is extracted from water
(D) water is converted into steam to produce electricity
Answer:
(A) potential energy possessed by stored water is converted into electricity

Question 7.
Choose the incorrect statement regarding wind power.
(A) It is expected to harness wind power to the maximum in open space.
(B) The potential energy content of wind blowing at high altitudes is the source of wind power.
(C) Wind hitting at the blades of a windmill causes them to rotate. The rotation thus achieved can be utilised further.
(D) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator.
Answer:
(B) The potential energy content of wind blowing at high altitudes is the source of wind power.

Question 8.
Which of the following is considered as the ultimate source of energy to us?
(A) Wind
(B) Waves of the ocean
(C) Heat in the interior of the earth
(D) Sun
Answer:
(D) Sun

Question 9.
The chief constituent of biogas is
(A) hydrogen
(B) carbon dioxide
(C) methane
(D) carbon
Answer:
(C) methane

Question 10.
A conventional source of energy from among the following is
(A) bio energy
(B) solar energy
(C) tidal energy
(D) natural gas
Answer:
(D) natural gas

Question 11.
An example of a fossil fuel is
(A) hydrogen
(B) natural gas
(C) firewood
(D) biogas
Answer:
(B) natural gas

Question 12.
A renewable source of energy is
(A) coal
(B) petrol
(C) natural gas
(D) firewood
Answer:
(D) firewood

Question 13.
A good fuel should have
(A) high calorific value and moderately high ignition point
(B) low calorific value and high ignition point
(C) low calorific value and moderately low ignition point
(D) very low ignition temperature and low calorific value
Answer:
(A) high calorific value and moderately high ignition point

Question 14.
The degradation of biomass in a biogas plant takes place by
(A) aerobic respiration by microbes such as bacteria
(B) aerobic respiration by worms and insects
(C) anaerobic respiration by microbes such as bacteria
(D) chemical activity between the inorganic molecules of the biogas.
Answer:
(C) anaerobic respiration by microbes such as bacteria

Question 15.
Which one of the following is not true about a box type solar cooker?
(A) The glass plate used in the box helps in the retention of heat.
(B) It can produce temperatures up to about 400°C.
(C) It takes long time to cook the food.
(D) It helps to maintain the nutrients in the food.
Answer:
(B) It can produce temperatures up to about 400°C.

Question 16.
Choose the incorrect statement from among the following:
(A) We are encouraged to plant more trees so as to ensure clean environment and also provide biomass fuel.
(B) Gobar gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen.
(C) The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash.
(D) Bio-mass is a renewable source of energy.
Answer:
(C) The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash.

Question 17.
In a hydroelectric power plant, more electrical power can be generated if water falls from a greater height because
(A) its temperature increases
(B) larger amount of potential energy is converted into kinetic energy
(C) the electricity content of water increases with height
(D) more water molecules dissociate into ions.
Answer:
(B) larger amount of potential energy is converted into kinetic energy

Question 18.
The major problem associated with nuclear fission energy is
(A) splitting of heavy nuclei
(B) sustaining chain reaction of fission
(C) converting nuclear energy into electrical energy
(D) safe disposal of spent nuclear fuel.
Answer:
(D) safe disposal of spent nuclear fuel.

Question 19.
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) Nuclear energy