1

### AIPMT 2015 Cancelled Paper

If in a p-n junction, a square input signal of 10 V is applied, as shown,

then the output across RL will be
A
B
C
D

## Explanation

Here P-N junction diode rectifies half of the ac wave i.e., acts as half wave rectifier.
During + ve half cycle Diode is forward biased output across RL will be

During –ve half cycle Diode is reverse biased output will not obtained.
2

### AIPMT 2015 Cancelled Paper

Which logic gate is represented by the following combination of logic gates ?

A
AND
B
NOR
C
OR
D
NAND

## Explanation

The Boolean expression of this arrangement is

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

Thus, the combination represents AND gate.
3

### AIPMT 2015

In the given figure, a diode D is connected to an external resistance R = 100 $\Omega$ and an e.m.f. of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the citcuit will be

A
20 mA
B
35 mA
C
30 mA
D
40 mA

## Explanation

Potential difference across resistance R

= 3.5 – 0.5 = 3.0 V

Current in circuit, I = V/R = 3/100 = 30 mA
4

### AIPMT 2015

The input signal given to a CE amplifier having a voltage gain of 150 is Vi = 2cos(15t + ${\pi \over 3}$). The corresponding output signal will be
A
2cos$\left( {15t + {{5\pi } \over 6}} \right)$
B
300cos$\left( {15t + {{4\pi } \over 3}} \right)$
C
300cos$\left( {15t + {{\pi } \over 3}} \right)$
D
75cos$\left( {15t + {{2\pi } \over 3}} \right)$

## Explanation

Given, Vi = 2cos(15t + ${\pi \over 3}$)

and Voltage gain AV = 150

For CE transistor phase difference between input and output signal is $\pi$ = 180o

Using formula, AV = ${{{V_0}} \over {{V_i}}}$

$\Rightarrow$ V0 = AV $\times$ Vi

= 150$\times$2cos(15t + ${\pi \over 3}$ + $\pi$)

= 300cos$\left( {15t + {{4\pi } \over 3}} \right)$