Answer: A good source of energy should have the following characteristics:
(i) It should do a large amount of work per unit mass or volume.
(ii) It should be easily available.
(iii) It should be easy to store and transport.
(iv) It should be economical.
2. What is a good fuel?
Answer: A good fuel is one that produces a large amount of heat per unit mass, is easily available, is easy to store and transport, and is economical. It should also burn easily at a moderate rate and produce less harmful smoke and residue.
3. If you could use any source of energy for heating your food, which one would you use and why?
Answer: I would use LPG for heating food. It has a high calorific value, burns with a clean blue flame without smoke or ash, and its flame can be easily controlled. It is convenient, efficient, and easily available, making it the best source for cooking.
Internal Question and Answer:
1. What are the disadvantages of fossil fuels?
Answer: The disadvantages of fossil fuels are:
(i) Pollution: Burning fossil fuels releases harmful gases like carbon dioxide, sulphur dioxide and nitrogen oxides, causing air pollution and acid rain.
(ii) Global warming: Carbon dioxide is a greenhouse gas, so it contributes to global warming.
(iii) Non-renewable: Fossil fuels are exhaustible and will get finished one day.
(iv) Mining hazards: Extraction of coal and oil causes environmental damage and risks to miners.
2. Why are we looking at alternate sources of energy?
Answer: We are looking at alternate sources of energy because fossil fuels like coal and petroleum are limited and will get exhausted. They also cause pollution. So we need renewable sources like solar, wind and hydro energy that are clean, inexhaustible and environment-friendly.
3. How has the traditional use of wind and water energy been modified for our convenience?
Answer: The traditional wind energy was used by sailboats and windmills to grind grain, while water energy ran waterwheels for grinding. Now, windmills generate electricity and water is used in hydroelectric power plants to produce electricity on a large scale for our convenience.
Answer: A concave mirror would be best suited for use in a solar cooker. A concave mirror can converge sunlight to a focal point, allowing for concentrated heat generation, which is essential for efficient cooking in a solar cooker.
2. What are the limitations of the energy that can be obtained from the oceans?
Answer: The energy obtained from the oceans has the following limitations:
(a) Tidal energy: Only a few places are suitable for building dams to harness tidal energy.
(b) Wave energy: It can be used only where ocean waves are sufficiently strong.
(c) Ocean thermal energy: It can be harnessed only when the temperature difference between the surface water and deeper water is at least 20°C. The power plants required are also expensive to maintain.
3. What is geothermal energy?
Answer: Geothermal energy is the heat energy present inside the Earth. This energy can be used to generate electricity by utilising the hot rocks, steam and hot water found beneath the Earth's surface.
4. What are the advantages of nuclear energy?
Answer: Nuclear energy has several advantages. A small amount of nuclear fuel releases a huge amount of energy, so less fuel is needed. It does not produce smoke, ash, or carbon dioxide, so it is a clean fuel. Nuclear power plants can work continuously for long periods and are not affected by weather. This makes nuclear energy a reliable and efficient source of electricity.
Answer: No source of energy can be considered completely pollution-free. Even renewable sources of energy may cause some pollution during the manufacture, installation and maintenance of the devices used to harness them. However, some sources, such as solar energy and wind energy, cause very little pollution during their use.
2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Answer: Yes, hydrogen is considered a cleaner fuel than CNG because burning hydrogen produces water as the main product, whereas burning CNG produces carbon dioxide and water. Carbon dioxide contributes to global warming. Therefore, hydrogen is a cleaner fuel than CNG, provided it is produced using clean energy sources.
1. Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer: Two renewable sources of energy are solar energy and wind energy. Solar energy is renewable because the Sun continuously provides energy, and wind energy is renewable because winds are naturally produced due to the uneven heating of the Earth's surface. Both sources are naturally replenished and will not be exhausted by their use.
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:
(i) Coal : It is a fossil fuel formed over millions of years. Once used up, it cannot be replenished quickly, so it will get exhausted.
(ii) Petroleum: It is also a fossil fuel. Its reserves are limited, and it takes millions of years to form, so it will run out one day.
(a) a sunny day. (b) a cloudy day.
(c) a hot day. (d) a windy day.
Answer: (b) a cloudy day.
[ A solar water heater works using sunlight. On a cloudy day, sunlight is blocked by clouds, so the solar panels cannot collect enough heat to warm the water.]
2. Which of the following is not an example of a bio-mass energy source?
(a) wood (b) gobar-gas (c) nuclear energy (d) coal
Answer: (c) nuclear energy
[ Nuclear energy is obtained from the nucleus of atoms through nuclear fission or fusion. ]
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?
(a) geothermal energy (b) wind energy (c) nuclear energy (d) bio-mass.
Answer: (c) nuclear energy
[ Nuclear energy comes from the nucleus of atoms, not from the Sun. Nuclear energy is the one that is not ultimately derived from the Sun's energy.]
4. Compare and contrast fossil fuels and the Sun as direct sources of energy.
Answer : Fossil fuels and the Sun are both sources of energy, but they differ in the following ways:
|
Fossil Fuels |
Sun |
|
They are exhaustible sources of energy. |
It is a renewable source of energy. |
|
They take millions of years to form. |
Solar energy is continuously available from the Sun. |
|
Their burning causes air pollution and releases carbon dioxide. |
Solar energy does not cause pollution during its use. |
|
They are stored in the Earth's crust. |
Solar energy is received directly from the Sun. |
5. Compare and contrast bio-mass and hydro electricity as sources of energy.
Answer : Biomass and hydroelectricity are both renewable sources of energy, but they differ in the following ways:
|
Biomass |
Hydroelectricity |
|
It is obtained from plant and animal wastes, such as wood, cow dung and crop residues. |
It is produced by using the energy of flowing or falling water. |
|
It is burnt directly or converted into fuels like biogas to obtain energy. |
It is generated by using flowing water to turn turbines. |
|
Burning biomass may cause air pollution. |
It does not cause air pollution during electricity generation. |
|
It can be replenished if biomass is used sustainably. |
It is renewable because water is replenished through the water cycle. |
6. What are the limitations of extracting energy from—
(a) the wind? (b) waves? (c) tides?
Answer : (a) Wind: Wind energy can be used only when the wind blows at a sufficient speed. Windmills require a large area of land and the initial cost of installation is high.
(b) Waves: Wave energy can be harnessed only at places where ocean waves are sufficiently strong. The technology required to extract this energy is also expensive.
(c) Tides: Tidal energy can be harnessed only at a few places where suitable tidal conditions exist. Building dams to utilise tidal energy is expensive.
7. 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?
Answer : (a) Energy sources are classified as renewable and non-renewable based on their ability to be replenished naturally. Renewable sources can be replenished in a short period, whereas non-renewable sources take millions of years to form.
(b) Energy sources are classified as exhaustible and inexhaustible based on whether they can be exhausted by human activities. Exhaustible sources are available in limited quantities, whereas inexhaustible sources are available in unlimited quantities.
No, the options are not exactly the same. Renewable and non-renewable sources are classified based on their replenishment, while exhaustible and inexhaustible sources are classified based on their availability and the possibility of being used up.
8. What are the qualities of an ideal source of energy?
Answer: An ideal source of energy should have the following qualities:
(i) It should provide a large amount of energy per unit mass or volume.
(ii) It should be easily available.
(iii) It should be easy to store and transport.
(iv) It should be economical.
(v) It should cause minimum pollution to the environment.
9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Answer: Advantages of a solar cooker:
(a) It uses solar energy, which is a renewable and pollution-free source of energy.
(b) It does not require any fuel, so it saves money.
(c) It does not produce smoke or harmful gases.
Disadvantages of a solar cooker:
(a) It cannot be used at night or on cloudy days.
(b) It takes more time to cook food than conventional cookers.
Solar cookers have limited use in places where sunlight is insufficient for most of the year, such as regions with frequent rainfall or heavy cloud cover.
10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Answer: The environmental consequences of increasing energy demand:
(a) Air pollution: Burning fossil fuels releases harmful gases like CO₂, SO₂, and nitrogen oxides, causing acid rain and breathing problems.
(b) Global warming: Excess CO₂ traps heat in the atmosphere, leading to the greenhouse effect and climate change.
(c) Depletion of resources: Fossil fuels like coal and petroleum are being used up rapidly and will soon run out.
(d) Land and water pollution: Mining, drilling and nuclear waste contaminate land and water sources.
(e) Damage to ecosystems: Building dams and power plants disturbs forests and wildlife.
Steps to reduce energy consumption:
(i) Use public transport, cycle, or walk instead of private vehicles.
(ii) Switch off lights, fans and appliances when not in use.
(iii) Use energy-efficient devices like LED bulbs and star-rated appliances.
(iv) Promote renewable energy like solar and wind power.
(v) Reduce, reuse and recycle materials to save energy used in manufacturing.
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