1

### AIPMT 2005

In a p-n junction photo cell, the value of the photo-electromotive force profuced by monochromatic light is proportional to
A
The barrier voltage at the p-n junction.
B
The intensity of the light falling on the cell.
C
The frequency of the light falling on the cell.
D
The voltage applied at the p-n junction.

## Explanation

Electromotive force depends on intensity of light that falls on it and does not depend on the frequency.
2

### AIPMT 2005

Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 $\mathop A\limits^ \circ$. The value of lattice constant for this lattice is
A
2.54 $\mathop A\limits^ \circ$
B
3.59 $\mathop A\limits^ \circ$
C
1.27 $\mathop A\limits^ \circ$
D
5.08 $\mathop A\limits^ \circ$

## Explanation

Lattice constant for (f.c.c.)

= a = interatomic spacing $\times$ $\sqrt 2$ = 3.59 $\mathop A\limits^ \circ$
3

### AIPMT 2005

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)si and (Eg)Ge respectively. Which one of the following relationships is true in their case?
A
(Eg)C > (Eg)Si
B
(Eg)C < (Eg)Si
C
(Eg)C = (Eg)Si
D
(Eg)C < (Eg)Ge.

## Explanation

Band gap of carbon is 5.5 eV while that of silicon is 1.1 eV

$\therefore$ (Eg)C $>$ (Eg)Si
4

### AIPMT 2005

Zener diode is used for
A
amplification
B
rectification
C
stabilisation
D
producing oscillations in an oscillator.

## Explanation

Zener diode is used for stabilisation while p-n junction diode is used for rectification.