### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2002

By increasing the temperature, the specific resistance of a conductor and a semiconductor
A
increases for both
B
decreases for both
C
increases, decreases
D
decreases, increases

## Explanation

Specific resistance is resistivity which is given by

$\rho = {m \over {m{e^2}\,\tau }}$

where $n=no.$ of free electrons per unit volume and $\tau$ $=$ average relaxation time

For a conductor with rise in temperature $n$ increases and $\tau$ decreases. But decrease in $\tau$ is more dominant than increase in $n$ resulting an increase in the value of $\rho$

For a semiconductor with rise in temperature, $n$ increases and $\tau$ decreases. But the increase in $n$ is more dominant than decrease in $\tau$ resulting in decrease in the value of $\rho .$
2

### AIEEE 2002

Formation of covalent bonds in compounds exhibits
A
wave nature of electron
B
particle nature of electron
C
both wave and particle nature of electron
D
none of these

## Explanation

Formation of covalent bond is best explained by molecular orbital theory.
3

### AIEEE 2002

At absolute zero, Si acts as
A
non-metal
B
metal
C
insulator
D
none of these

## Explanation

Pure silicon, at absolute zero, will contain all the electrons in bounded state. The conduction band will be empty. So there will be no free electrons (in conduction band) and holes (in valence band) due to thermal agitation. Pure silicon will act as insulator.