Question

(a) Describe briefly, with the help of a diagram, the role of the two important processes involved in the formation of a p-n junction.

(b) Name the device which is used as a voltage regulator. Draw the necessary circuit diagram and explain its working.

Answer 1

(a) For diagram see Q.N.1 (a) (L.A.T.Q) The two processes are 

(i) Diffusion

(ii) Drift

Diffusion : Holes diffuse from p-side to n-side (p→n) (p→n) a and electrons diffuse from n-side to p-side (n→p).

Drift :  The motion of charge carriers, due to the applied electric field (vactorE) which results in drifting of holes along (vactorE) and of electrons opposite to that of electric field (vactorE)

(b) Name of device : Zener Diode

Working :  Any increase / decrease in the input voltage results in an increase / decrease of the voltage drop across R_s, without any change in voltage across the zener diode. Thus Zener diode acts as a voltage regulator.