### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2004

When $p$-$n$ junction diode is forward biased then
A
both the depletion region and barrier height are reduced
B
the depletion region is widened and barrier height is reduced
C
the depletion region is reduced and barrier height is increased
D
both the depletion region and barrier height are increased

## Explanation

Both the depletion region and barrier height is reduced.
2

### AIEEE 2004

For a transistor amplifier in common emitter configuration for load impedance of $1k\,\Omega$ $\left( {{h_{fe}} = 50} \right.$ and $\left. {{h_{oe}} = 25} \right)$ the current gain is
A
$-24.8$
B
$-15.7$
C
$-5.2$
D
$-48.78$

## Explanation

In common emitter configuration current gain

${A_i} = {{ - h{f_e}} \over {1 + {b_{0c}}{R_L}}}$

$= {{ - 50} \over {1 + 25 \times {{10}^{ - 6}} \times 1 \times {{10}^3}}}$

$= - 48.78$
3

### AIEEE 2004

The manifestation of band structure in solids is due to
A
Bohr's correspondence principle
B
Pauli's exclusion principle
C
Heisenberg's uncertainty principle
D
Boltzmann's law

## Explanation

Pauli's exclusion principle.
4

### AIEEE 2004

A piece of copper and another of germanium are cooled from room temperature to $77K,$ the resistance of
A
copper increases and germanium decreases
B
each of them decreases
C
each of them increases
D
copper decreases and germanium increases

## Explanation

Copper is a conductor, so its resistance decreases on decreasing temperature as thermal agitation decreases; whereas germanium is semiconductor therefore on decreasing temperature resistance increases.