### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2005

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than $2480$ $nm$ is incident on it. The band gap in $(eV)$ for the semiconductor is
A
$2.5$ $eV$
B
$1.1$ $eV$
C
$0.7$ $eV$
D
$0.5$ $eV$

## Explanation

Band gap $=$ energy of photon of wavelength $2480$ $nm.$ So,

$\Delta E = {{hc} \over \lambda }$

$= \left( {{{6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}} \over {2480 \times {{10}^{ - 9}}}}} \right) \times {1 \over {1.6 \times {{10}^{ - 19}}}}eV$

$= 0.5\,eV$
2

### 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.
3

### 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

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

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

$= - 48.78$
4

### 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.