1

### AIPMT 2004

In semiconductors at a room temperature
A
the valence band is partially empty and the conduction band is partially filled
B
the valence band is completely filled and the conduction band is partially filled
C
the valence band is completely filled
D
the conduction band is completely empty

## Explanation

In semiconductors at room temperature the electrons get enough energy so that they are able to over come the forbidden gap. Thus at room temperature the valence band is partially empty and conduction band is partially filled. Conduction band in semiconductor is completely empty only at 0 K.
2

### AIPMT 2004

The peak voltage in the output of a half wave diode rectifier fed with a sinusoidal signal without filter is 10 V. The d.c. component of the output voltage is
A
(10/$\sqrt 2$) V
B
$\left( {{{10} \over \pi }} \right)V$
C
10 V
D
(20/$\pi$) V

## Explanation

V = ${{{V_0}} \over \pi }$

$\Rightarrow$ V = $\left( {{{10} \over \pi }} \right)V$
3

### AIPMT 2003

Barrier potential of a p-n junction diode does not depened on
A
diode design
B
temperature
C
forward bias
D
doping density

## Explanation

Barrier potential does not depend in diode design while barrier potential depends upon temperature, doping density and forward biasing.
4

### AIPMT 2003

If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be
A
25 Hz
B
50 Hz
C
70.7 Hz
D
100 Hz

## Explanation

In full wave rectifier the fundamental frequency in ripple is twice of input frequency.