1

### 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
2

### AIPMT 2006

The following figure shows a logic gate circuit with two inputs A and B and the output C.

The voltage waveforms of A, B and C are as shown below.

The logic circuit gate is
A
OR gate
B
AND gate
C
NAND gate
D
NOR gate

## Explanation

The truth table corresponding to waveform is given by

$\matrix{ A & B & C \cr 1 & 1 & 1 \cr 0 & 1 & 0 \cr 1 & 0 & 0 \cr 0 & 0 & 0 \cr }$

$\therefore$ The given logic circuit gate is AND gate.
3

### AIPMT 2005

In a p-n junction photo cell, the value of the photo-electromotive force profuced by monochromatic light is proportional to
A
The barrier voltage at the p-n junction.
B
The intensity of the light falling on the cell.
C
The frequency of the light falling on the cell.
D
The voltage applied at the p-n junction.

## Explanation

Electromotive force depends on intensity of light that falls on it and does not depend on the frequency.
4

### AIPMT 2005

Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 $\mathop A\limits^ \circ$. The value of lattice constant for this lattice is
A
2.54 $\mathop A\limits^ \circ$
B
3.59 $\mathop A\limits^ \circ$
C
1.27 $\mathop A\limits^ \circ$
D
5.08 $\mathop A\limits^ \circ$

## Explanation

Lattice constant for (f.c.c.)

= a = interatomic spacing $\times$ $\sqrt 2$ = 3.59 $\mathop A\limits^ \circ$