Important Points

  • Renewable sources of energy are those sources of energy which are continuously produced in nature and are practically inexhaustible. Examples of renewable source of energy are solar energy, wind energy, energy of flowing water, tidal energy, ocean wave energy, geothermal energy, etc.
  • Non-renewable sources of energy are those sources of energy which are likely to be exhausted in coming future, these are also called conventional sources of energy. Examples of non-renewable sources of energy are petroleum, coal and the natural gas.
  • Nuclear fuels are partly renewable and partly non-renewable.
  • The energy which we obtain from the sun is called solar energy.
  • Solar constant is the amount of energy received by unit are when placed perpendicular to the direction of the sun’s rays in one second if the distance between the unit area and the sun is equal to the distance between the earth and the sun. Its value is 1400 W/m2.
  • Main components of the solar energy are infrared rays, visible light and ultraviolet rays.
  • Ultraviolet rays have wavelength shorter than that of visible violet light. These rays may cause skin cancer if our body is exposed to these rays. Ultraviolet rays are invisible and are absorbed by ozone layer present in the upper atmosphere.
  • Visible light is that part of solar spectrum which produces visible sensation in our eye. It consists of seven colours and its wavelength ranges from 400 nm to 700 nm.
  • Devices used for harnessing solar energy are called solar energy devices. Solar energy devices are of two types: (i) in which solar energy is collected as heat and (ii) those which convert solar energy into electricity.
  • Black painted surface absorbs most of the heat which is incident on it that is why black painted surfaces are used in solar energy devices.
  • Solar cell is a devices which converts solar energy directly into electricity. The materials which are commonly used for making solar cells are germanium, silicon and gallium.
  • Moving air is called wind. Wind energy is related to solar energy.
  • In ancient times the wind energy was used for winnowing, in sail boats and in windmills for grinding grains.
  • Windmill is a machine which works from the energy of wind.
  • Flowing water has kinetic energy. Energy of water has been used by men from ancient times for grinding grains by water wheels, transporting heavy logs of wood from inaccessible areas of forests in hilly regions.
  • Hydroelectric power plant is used to produce electricity from the energy of flowing water on large scale.
  • Energy can be obtained from the oceans mainly in three ways:
    a) Tidal energy
    b) Ocean waves energy and
    c) Ocean thermal energy (OTE)
  • The waste material of living organisms (animal dung) and dead bodies of living organisms (plants, animals) is called biomass.
  • Energy obtained from biomass of animals and plants is called bio-energy.
  • Charcoal is obtained from wood by destructive distillation. Other products of destructive distillation of wood are tar, wood gas, methyl alcohol and acetic acid.
  • Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide.
  • Coal is a mixture of compounds of carbon, hydrogen and oxygen but its main constituent is carbon only. Coal is of four types:
    i) Peat
    ii) Lignite
    iii) Bituminous
    iv) Anthracite
  • Coal is used as a source of heat in homes and industries and in thermal plants to generate electricity.
  • Petroleum is a complex mixture of hydrocarbons, nitrogen and sulphur. The process of separating crude petroleum into useful components is called refining. Refining of petroleum is done by the process of fractional distillation.
  • Various components of fractional distillation of petroleum are:
    i) Petroleum gas
    ii) gasoline or petrol
    iii) kerosene
    iv) diesel
    v) fuel oil
    vi) lubricating oil
    vii) paraffin wax
    viii) asphalt
  • Main constituents of petroleum gas is butane. It can be liquefied by application of pressure which is called Liquefied Petroleum Gas (LPG), which is used as cooking gas.
  • Advantages of LPG are that is a clean and neat fuel and has high calorific value.
  • Natural gas is fossil fuel which contains methane and little amount of ethane and propane. Natural gas was formed due to the decomposition of plants under water carried out by anaerobic bacteria in the absence of air.
  • Natural gas is used as a fuel in homes and industries and a source of carbon and hydrogen in tyre and fertiliser industry respectively.
  • Natural gas is a complete fuel with high calorific value.
  • Nuclear fission in the phenomenon of splitting a heavy nuclei into two or more lighter nuclei along with the release of tremendous amount of energy.
  • The process in which two lighter nuclei combine to form a heavy and more stable nucleus with liberation of huge amount of energy is called nuclear fission.
  • Nuclear reactor is a device or nuclear furnace in which nuclear energy is produced under a self-sustaining controlled nuclear fission chain reaction.
  • A nuclear reactor works on the principle of controlled fission chain reaction which is self-sustained.
  • Nuclear reactor is used for generating electric power, propelling ships and submarines, producing man-made isotopes which are used in medicine, industry, agriculture, etc. Research reactors serve as a source of neutrons which are used for different experiments such as nuclear reactions and neutron scattering.