1

### 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
2

### AIPMT 2001

The given truth table is for which logic gate

$\matrix{ A & B & Y \cr 1 & 1 & 0 \cr 0 & 1 & 1 \cr 1 & 0 & 1 \cr 0 & 0 & 1 \cr }$
A
NAND
B
XOR
C
NOR
D
OR

## Explanation

This truth table represents NAND gate. 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).