1

### 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
2

### 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$\left( {15t + {{4\pi } \over 3}} \right)$
3

### 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.
4

### AIPMT 2014

The given graph represents V-I characteristic for a semiconductor device. Which of the following statement is correct ?
A
It is V-I characteristic for solar cell where, point A represents open circuit voltage and point B short circuit current.
B
It is for a solar cell and popints A and B represent open circuit voltage and current, respectively.
C
It is for a photodiode and points A and B represent open circuit voltage and current, respectively.
D
It is for a LED and points A and B represent open circuit voltage and short circuit current, respectively.

## Explanation

The V-I characteristic for a solar cell is as shown the figure. 