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1

### AIPMT 2001

The current in the circuit will be

A
5/40 A
B
5/50 A
C
5/10 A
D
5/20 A

## Explanation

D1 is reverse biased and D2 is forward biased.

$$\therefore$$ I = $${5 \over {30 + 20}}$$ = $${5 \over {50}}$$ A
2

### AIPMT 2001

For a common base circuit if $${{{I_C}} \over {{I_E}}}$$ = 0.98 then current gain for common emitter circuit will be
A
49
B
98
C
4.9
D
25.5.

## Explanation

$${{{I_C}} \over {{I_E}}}$$ = 0.98 = $$\alpha$$

$$\therefore$$ Current gain, $$\beta$$ = $${{{I_C}} \over {{I_B}}}$$ = $${\alpha \over {1 - \alpha }}$$ = 49
3

### AIPMT 2000

The correct relation for $$\alpha$$, $$\beta$$ for a transistor
A
$$\beta = {{1 - \alpha } \over \alpha }$$
B
$$\beta = {\alpha \over {1 - \alpha }}$$
C
$$\alpha = {{\beta - 1} \over \beta }$$
D
$$\alpha \beta = 1$$

## Explanation

$$\beta$$ = $${{{I_C}} \over {{I_B}}}$$ = $${{{I_C}} \over {{I_E} - {I_C}}}$$ = $${{{{{I_C}} \over {{I_E}}}} \over {1 - {{{I_C}} \over {{I_E}}}}}$$ = $${\alpha \over {1 - \alpha }}$$
4

### AIPMT 2000

From the following diode circuit, which diode is in forward biased condition
A
B
C
D

## Explanation

A diode is said to be forward biased if p-type semiconductor of p-n junction is at positive potential with respect to n-type semiconductor of p-n junction. It is so for circuit (a).

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