1
MCQ (Single Correct Answer)

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.
2
MCQ (Single Correct Answer)

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
3
MCQ (Single Correct Answer)

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$$\left( {15t + {{4\pi } \over 3}} \right)$$
4
MCQ (Single Correct Answer)

AIPMT 2014

The barrier potential of a p-n junction depends on
(1)   type of semiconductor material
(2)   amount of doping

(3)   temperature

Which one of the following is correct ?
A
(1) and (2) only
B
(2) only
C
(2) and (3) only
D
(1), (2) and (3)

Explanation

The barrier potential depends on type of semiconductor (For Si, Vb = 0.7 V and for Ge, Vb = 0.3 V), amount of doping and also on the temperature.

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