Semi-conductors are certain type, of metals which allow only partial current to pass through them in one direction only. In a solar cell, the pieces(wafers) of semi-conductor materials containing impurities are so arranged that potenti,ll difference develops between two regions of the semi-conductors when light falls on it . A lead storage battery is connected in the circuit which gets charged and can be used as and when desired.
(i) How does conductivity of semi-conductors increases ?
(ii) Name any four materials which act as a semiconductor .

Explanation

(i) Conductivity of semi-conductors increases when light falls on them and certain impurities are added to them.
(ii) Materials like Silicon, Selenium, Cadmium sulphide and Copper sulphide act as semi-conductors.