1

### AIPMT 2007

In the following circuit, the output Y for all possible inputs A and B is expressed by the truth table. A
$\matrix{ A & B & Y \cr 0 & 0 & 1 \cr 0 & 1 & 1 \cr 1 & 0 & 1 \cr 1 & 1 & 0 \cr }$
B
$\matrix{ A & B & Y \cr 0 & 0 & 1 \cr 0 & 1 & 0 \cr 1 & 0 & 0 \cr 1 & 1 & 0 \cr }$
C
$\matrix{ A & B & Y \cr 0 & 0 & 0 \cr 0 & 1 & 1 \cr 1 & 0 & 1 \cr 1 & 1 & 1 \cr }$
D
$\matrix{ A & B & Y \cr 0 & 0 & 0 \cr 0 & 1 & 0 \cr 1 & 0 & 0 \cr 1 & 1 & 1 \cr }$

## Explanation

Y' = $\overline {A + B}$

Y = $\overline {Y'}$

Y = $\overline{\overline {A + B}}$

Y = A + B which is OR-gate.
2

### AIPMT 2007

Which one of the following represents forward bias diode ?
A B C D ## Explanation

A diode is said to be forward biased if p-side is at higher potential than n-side of p-n junction.
3

### AIPMT 2006

Which one of the following represents forward bias diode ?
A B C D ## Explanation

A diode is said to be forward biased if p-side is at higher potential than n-side of p-n junction.
4

### AIPMT 2006

A transistor is operated in common emitter configuration at constant collector voltage VC = 1.5 V such that a change in the base current from 100 $\mu$A to 150 $\mu$A profuces a change in the collector current from 5 mA to 10 mA. The current gain $\beta$ is
A
50
B
67
C
75
D
100

## Explanation

Current gain, $\beta$ = ${{\Delta {I_C}} \over {\Delta {I_B}}}$

= ${{\left( {10 - 5} \right) \times {{10}^{ - 3}}} \over {\left( {150 - 100} \right) \times {{10}^{ - 6}}}}$ = 100