Question: Q. 3. (i) Describe briefly, with the help of a diagram, the roleof the two important processes involved in the formation of a $p-n$ junction.
Name the device which is used as a voltage regulator. Draw the necessary circuit diagram and explain its working.
U] R [OD I, II, III 2012]
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Solution:
Ans. (i) For diagram see Q. 1(a) Long Answer Type Questions.
The two processes are
(a) Diffusion
(b) Drift
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Diffusion : Holes diffuse from $p$-side to $n$-side $(p \rightarrow n)$ and electrons diffuse from $n$-side to $p$-side $(n \rightarrow p)$.
Drift : The motion of charge carriers, due to the applied electric field $(\vec{E})$ which results in drifting of holes along $\vec{E}$ and of electrons opposite to that of electric field $(\vec{E})$.
(ii) Name of device : Zener Diode 1 [Note : for diagram see Q. 4 (ii) (SATQ-II)] 1 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.
[CBSE Marking Scheme, 2012] 1/2
