Question

(a) Explain the principle of working of a hydroelectric power plant.
(b) What is tidal energy? How can it be utilized?
(c) State any two uses of solar cells.
(d) Explain why, a solar cooker box is (i) painted black from inside, and (ii) covered with a glass sheet.
​(e) Give two reasons why Biogas is a good domestic fuel.

Answer 1

(a) The principle of hydropower is that the potential energy of the water stored at great heights in the dam is converted into kinetic energy by allowing the water to flow at high speed. The high-speed water then falls on a turbine, which is connected to a generator. The kinetic energy of the water gets converted into mechanical energy, which rotates the shaft of the generator, which further produces electricity and the mechanical energy gets converted into electrical energy.

(b) Energy due to the movement of the water in areas with high tidal movements is known as tidal energy. Few large underwater turbines are placed in areas with high tidal movements. Then the kinetic energy of the tidal water is used to rotate the turbine, which is connected to a generator to produce electricity. So, tidal energy is mainly used to generate electricity like hydroelectric power plants.

(c) (i) Solar cells are used to make handheld calculators or wrist watches
(ii) Solar cells are used to convert light energy from the sun into electrical energy.

(d) (i) Solar cooker box is painted black so that it can absorb most of the sunlight which falls on it.
(ii) Solar cooker box is covered with a glass sheet so that the absorbed heat from the sunlight can be trapped inside the box and the temperature inside the box can be increased to cook the food.

(e) Biogas is considered as good fuel because of the following reasons:
(i) Biogas does not cause air pollution.
(ii) Biogas produces a large amount of heat per unit mass.