1

### AIPMT 2012 Prelims

The figure shows a logic circuit with two inputs A and B and the output C. The voltage wave forms across A, B and C are as given. The logic circuit gate is
A
OR gate
B
NOR gate
C
AND gate
D
NAND gate

## Explanation

The truth table is
The logic circuit is OR gate.
2

### AIPMT 2012 Prelims

Transfer characteristics [output voltage (V0) vs input voltage (Vi)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used

A
in region III
B
both in region (I) and (III)
C
in region II
D
in region I

## Explanation

In the given graph,

Region (I) – Cutoff region

Region (II) – Active region

Region (III) – Saturation region

Using transistor as a switch it is used in cutoff region or saturation region.

Using transistor as a amplifier it is used in active region.
3

### AIPMT 2012 Prelims

C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator where as Si is intrinsic semiconductor. This is because
A
In case of C the valence band is not completely filled at absolute zero temperature.
B
In case of C the conduction band is partly filled even at absolute zero temperature.
C
The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.
D
The four bonding electrons in the case of C lie in the third orbit , whereas for Si they lie in the fourth orbit.

## Explanation

Electronic configuration of 6C

6C = 1s2, 2s2 2p2

The electronic configuration of 14Si

14Si = 1s2, 2s2 2p6, 3s2 3p2

As they are away from Nucleus, so effect of nucleus is low for Si even for Sn and Pb are almost mettalic.
4

### AIPMT 2012 Prelims

Two ideal diodes are connected to a battery as shown in the circuit. The current supplied by the battery is

A
0.75 A
B
zero
C
0.25 A
D
0.5 A

## Explanation

Here D1 is in forward bias and D2 is in reverse bias so, D1 will conduct and D2 will not conduct.
So, the current supplied by the battery is

I = ${5 \over {10}}$ = 0.5 A