### JEE Mains Previous Years Questions with Solutions

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1

### 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.
2

### AIEEE 2004

When $npn$ transistor is used as an amplifer
A
electrons move from collector to base
B
holes move from emitter to base
C
electrons move from base to collector
D
holes move from base to emitter

## Explanation

Electrons move from base to emmitter.
3

### AIEEE 2003

In the middle of the depletion layer of a reverse- biased $p$-$n$ junction, the
A
electric field is zero
B
potential is maximum
C
electric field is maximum
D
potential is zero

## Explanation

As in reverse bias, the current through the $0000$ is zero through the electric field is also zero.
4

### AIEEE 2003

The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the
A
crystal structure
B
variation of the number of charge carries with temperature
C
type of bonding
D
variation of scattering mechanism with temperature

## Explanation

When the temperature increases, certain bounded electrons become free which tend to promote conductivity. Simultaneously number of collisions between electrons and positive kernels increases