Class 10 Physics



Sources of Energy: NCERT Exercise Solution

What are the limitations of extracting energy from:

  • Wind

    Answer: Large tract of land is required for establishment of wind farms. They can be established only at those places where wind speed is high enough. Initial cost of establishing a wind farm is very high and the cost of maintenance is also high.
  • Waves

    Answer: Energy from waves can be harnessed only at selected places; only in coastal areas.
  • Tides

    Answer: Energy from tides can be harnessed only at selected places; only in coastal areas. Technologies for harnessing energy from waves and tides are still at experimental stage and hence are less efficient and very costly.

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

  • A sunny day
  • A cloudy day
  • A hot day
  • A windy day

    Answer: (b) A cloudy day

Which of the following is not an example of a bio-mass energy source?

  • Wood
  • Gobar-gas
  • Nuclear energy
  • Coal

    Answer: (c) Nuclear energy

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?

  • Geothermal energy
  • Wind energy
  • Nuclear energy
  • Bio-mass

    Answer: (c) Nuclear Energy

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

Answer: Sun is the direct source of energy, while fossil fuels are formed because of the solar energy stored in them. When green plants prepare food, they convert the solar energy into chemical energy which is stored in the form of biomass. The same biomass gets transferred to the animals. Thus, the energy in the form of biomass which is stored in fossil fuels has come from the sun.

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

Answer: Biomass and hydroelectricity are different in many aspects. Hydroelectricity is generated using the kinetic energy from moving water, while the energy from biomass is generated by decomposition of farm waste. Since biomass is composed of organic compounds so energy from biomass results in air pollution. Hydroelectricity, on the other hand, is pollution free.


On what basis would you classify energy sources as:

  • Renewable and non-renewable
  • Exhaustible and inexhaustible

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

Answer: Options given in (a) and (b) are almost same. An energy source which can be quickly renewed is called renewable or inexhaustible. On the other hand, the energy source which cannot be renewed in foreseeable future are called non-renewable or exhaustible.

What are the qualities of an ideal source of energy?

Answer: Characteristics of an ideal source of energy:

  • It should be able to do large amount of work for each unit of mass or volume.
  • It should be easily accessible.
  • It should be easily transported.
  • It should be economical.

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

Answer: Advantages of Solar Cooker:

  • They are environment friendly.
  • Use of a solar cooker does not involve recurring expenses on fuel.

Disadvantages of Solar Cooker:

  • Solar cooker is very slow.
  • Solar cooker can work only during summer months and is useless during winters and on cloudy days.
  • Solar cooker can be useful at those places which receive plenty of sunshine. This is useless in colder climates.

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

Answer: Environmental consequences of increasing demand for energy are as follows:

  • Use of fossil fuels is increasing air pollution which is not good for our health.
  • Air pollution is causing much damage to the ecosystem.
  • Greenhouse effect has resulted in global warming which is manifesting itself in strange changes in the weather pattern around the world.
  • Too much exploitation of fossil fuels is going to create a situation when there would be not fossil fuel.

Steps to reduce energy consumption:

  • Judicious use of energy is the only way.
  • Use public transport instead of private modes of transport.
  • Use bicycle whenever possible.
  • Walk for short distance commute.
  • Avoid unnecessary use of modern gadgets which consume lot of energy.
  • Get a solar water heater installed for winter.