1

### AIPMT 2009

A transistor is operated in common-emitter configuration at VC = 2V such that a change in the base current from 100 $\mu$A to 200 $\mu$A produces a change in the collector current from 5 mA to 10 mA. The current gain is
A
100
B
150
C
50
D
75

## Explanation

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

= ${{\left( {10 - 5} \right) \times {{10}^{ - 3}}} \over {\left( {200 - 100} \right) \times {{10}^{ - 6}}}}$ = 50
2

### AIPMT 2009

The symbolic representation of four logic gates are given below

The logic symbols for OR, NOT and NAND gates are respectively
A
(iv), (i), (iii)
B
(iv), (ii), (i)
C
(i), (iii), (iv)
D
(iii), (iv), (ii)

## Explanation

OR gate, NOT gate and NAND gates are (iv), (ii) and (i) respectively.
3

### AIPMT 2008

If the lattice parameter for a crystalline structure is 3.6 $\mathop A\limits^ \circ$, then the atomic radius in fcc crystal is
A
2.92 $\mathop A\limits^ \circ$
B
1.27 $\mathop A\limits^ \circ$
C
1.81 $\mathop A\limits^ \circ$
D
2.10 $\mathop A\limits^ \circ$

## Explanation

The atomic radius in a f.c.c. crystal is = ${a \over {2\sqrt 2 }}$

$\therefore$ Atomic radius = ${{3.6} \over {2\sqrt 2 }}$ = 1.27 $\mathop A\limits^ \circ$
4

### AIPMT 2008

The voltage gain of an amplifier with 9% negative feedback is 10. The voltage gain without feedback will be
A
1.25
B
100
C
90
D
10

## Explanation

Negative feedback is applied to reduce the output voltage of an amplifier. If there is no negative feedback, the value of output voltage could be very high. In the options given, the maximum value of voltage gain is 100. Hence it is the correct option.