CBSE Class 10 Science 2020 · Paper 31(B) · Question 4
Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts.
Geothermal energy is the energy harnessed from the heat of the Earth. The deeper regions of the Earth’s crust are extremely hot. This heat melts the rocks, and the molten rocks called magma formed in the deeper hot regions of the Earth’s core get pushed upwards and trapped in certain regions called “hot spots”. These hot spots become a source of geothermal energy. Underground water in contact with the hot spots turns into steam which gets compressed to very high pressure. This steam is extracted by linking pipes through holes drilled up to hot spots. The outcoming steam (at high pressure) rotates the turbine of an electric generator and produces electric energy. In our country one such place is located in Madhya Pradesh.
- (a)What is geothermal energy ?[1]
- (b)List two advantages of harnessing geothermal energy.[1]
- (c)State the role of turbine in an electric generator.[1]
- (d)Name and state the principle behind the electric generator.[1]
Answer
Geothermal energy is the Earth's heat, used through steam; it is cheap and always available; a generator works by electromagnetic induction.
(a) Geothermal energy is the energy harnessed from the heat of the Earth: molten rock trapped in hot spots heats underground water into high-pressure steam, which is used to produce electricity.
(b) Any two: the cost of production is low, since no fuel has to be burnt; it is available all the time; it is renewable; it causes far less pollution than burning fuels. The marking scheme lists the first two and accepts other correct advantages.
(c) The high-pressure steam rotates the turbine, and the turbine rotates the armature (coil) of the generator in the magnetic field: it converts the energy of the steam into the mechanical energy that the generator turns into electrical energy.
(d) Electromagnetic induction: when a coil is rotated in a magnetic field, the magnetic field through it changes and an electric current is induced in it. The generator uses mechanical energy to rotate a conductor in a magnetic field and so produces electricity.
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