Source of Energy
NCERT Solutions
NCERT Exercises
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
(b) A cloudy day
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
(c) Nuclear energy
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
(c) Nuclear energy
4. Compare and contrast fossil fuels and the sun as direct sources of energy.
Fossil fuels are non-renewable source of energy. It takes millions of years for the formation. It cannot be replenished.
Solar energy is renewable. It is abundant in nature. It can be replenished.
5. Compare and contrast bio-mass and hydroelectricity as sources of energy.
Biomass is a renewable source of energy and it is obtained from the dead plants and animals. Ex: Wood, gobar-gas.
Hydroelectricity is obtained from the potential energy of the stored water at a height. The electricity is produced through mechanical process. They are renewable source of energy. Ex: Dams and reservoirs.
6. What are the limitations of extracting energy from:
a. The wind?
b. Waves?
c. Tides?
a. Large number of wind mills is required to get a feasible amount of energy. To establish a large number of wind miss requires a large area. Also windmills requires a speed more than 15 km/h to generate electricity.
b. Very strong ocean waves are required to produce energy.
c. Very high tides are required for generating energy from tides. High tides results only when the sun, the moon and the earth comes in a straight alignment.
7. On what basis would you classify energy sources as:
a. Renewable and non-renewable?
b. Exhaustible and inexhaustible?
a) Renewable and non-renewable: Renewable energy is available in plenty. They can replenish themselves. Ex: Solar, Wind, Water etc. Non-renewable energy resources are available in limited. They take a long time to replenish. Ex: Oil, Nucler, Coal.
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. Ex: solar and wind energy.
8. What are the qualities of an ideal source of energy?
- Easy accessible
- Pollution free
- Economical
- Easy to store
- The amount of energy produced when burnt should be huge.
9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
The heat source, sunlight, which is renewable source of energy, which is abundant in nature, replenish themselves and they cause no pollution.
But manufacturing cost is high in case of solar cooker and It doesn’t work on a cloudy day.
10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
To meet the increased demand of energy fossil fuels are used because they are readily available. But increased usage of fossil fuels results in air pollution and large emission of carbon dioxide which paved the way for global warming.
By reducing the unnecessary usage of electricity and water as well as by using public transportation one can reduce the energy consumption.
Intext Exercises
Pg. No. 243
1. What is a good source of energy?
- It should not produce pollution
- Economical
- Easy to store and transport
- It should produce a large amount of heat.
2. What is a good fuel?
A good fuel should be easily available, easy to transport, and produce large amount of heat.
3. If you could use any source of energy for heating your food, which one would you use and why?
For heating and cooking, natural gas can be used. Because it is easily available and easy to transport. It does not produce huge amount of smoke when burnt.
Pg. No. 248
1. What are the disadvantages of fossil fuels?
- It causes air pollution.
- It creates global warming.
- Soil fertility is affected.
2. Why are we looking at alternate sources of energy?
Fossil fuels, which are non renewable, are mostly used by humans. By over usage, these fuel may disappear in the future.
3. How has the traditional use of wind and water energy been modified for our convenience?
In olden days, wind energy was trapped used windmills to do mechanical works like lifting or drawing water from a well. But today the kinetic energy of wind is trapped and converted into electricity with the help of wind mills.
Similarly, waterfalls were the source of potential energy in olden days. But today 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.
Pg. No. 253
1. What kind of mirror – concave, convex or plain would be best suited for use in a solar cooker? Why?
A concave mirror is used in solar cooker. Because it reflect the sunlight and focus the sunlight at one point. It increase in temperature and utilized for heating and cooking the food.
2. What are the limitations of the energy that can be obtained from the ocean?
- Strong waves are required for the tidal energy. But the relative positioning of the earth, the sun and the moon has an impact on the tidal energy.
- High dams are required for the conversion of tidal energy into electricity. But the construction and maintenance cost is very high.
3. What is geothermal energy?
Geothermal energy is a renewable energy taken from the Earth’s core. The energy can be obtained from the hot spots. They 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.
4. What are the advantages of nuclear energy?
- Large amount of energy is produced.
- Pollution is less.
- It is cheaper and low cost.
Pg. No. 253
1. Can any source of energy be pollution-free? Why or why not?
No source of energy is pollution free. Manufacturing of devices to make use of these energy may cause pollution.
2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Hydrogen gas is cleaner than CNG. CNG consist of hydrocarbons. Carbon is a form of pollutant in CNG. But hydrogen is waste-free .The fusion of hydrogen does not produce any waste. Hence, hydrogen as a rocket fuel is cleaner than the CNG.
Pg. No. 254
1. Name two energy sources that you would consider to be renewable. Give reasons for your choices.
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.
2. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
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.