(a) Explain solar cell panel.
(b) Give the principle of working of a windmill.

Explanation

(a) A solar cell is a device which converts solar energy directly into electricity. A group of solar cells is called a solar cell panel. It consists of a large number of solar cells. Joined together in a definite pattern. It provides a lot of electric energy required by artificial satellites, water pumps, street lighting, etc.
For joining the various solar cells in a solar panel, silver wires are used because silver (metal) is the best conductor of electricity having a very low resistance, which also increases the efficiency.
(b) When the blowing wind strikes the blades of a windmill, it exerts a force on them. As a result of this force, the blades of the windmill start rotating. The rotation of the blades of the windmill causes to and fro (or up to down) motion in the crank (or connecting rod). This rotary motion is used to turn the turbines of electric generators to produce electricity and also to drive a large number of machines like water pumps and flour mills.
A large number of windmills erected over a large area are known as a wind energy farm.