### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2008

A working transistor with its three legs marked $P,Q$ and $R$ is tested using a multi-meter. No conduction is found between $P$ and $Q$. By connecting the common (negative) terminal of the multi-meter to $R$ and the other (positive) terminal to $P$ or $Q,$ some resistance is seen on the multi-meter. Which of the following is true for the transistor?
A
It is an $npn$ transistor with $R$ as base
B
It is an $pnp$ transistor with $R$ as collector
C
It is an $pnp$ transistor with $R$ as emitter
D
It is an $npn$ transistor with $R$ as collector

## Explanation

It is a $n$-$p$-$n$ transistor with $R$ as base.
2

### AIEEE 2007

If in a $p$-$n$ junction diode, a square input signal of $10$ $V$ is applied as shown

Then the output signal across ${R_L}$ will be

A
B
C
D

## Explanation

The current will flow through ${R_L}$ when the diode is forward biased.
3

### AIEEE 2007

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate ?
A
The number of free electrons for conduction is significant only in $Si$ and $Ge$ but small in $C.$
B
The number of free conduction electrons is significant in $C$ but small in $Si$ and $Ge.$
C
The number of free conduction electrons is negligibly small in all the three.
D
The number of free electrons for conduction is significant in all the three

## Explanation

$Si$ and $Ge$ are semiconductors but $C$ is an insulator. Also, the conductivity of $Si$ and $Ge$ is more than $C$ because the valence electrons of $Si, Ge$ and $C$ lie in third, fourth and second orbit respectively.
4

### AIEEE 2006

If the lattice constant of this semiconductor is decreased, then which of the following is correct?
A
All ${E_c},{E_g},{E_v}$ increase
B
${E_c}$ and ${E_v}$ increase, but ${E_g}$ decreases
C
${E_c}$ and ${E_v}$ decrease, but ${E_g}$ increases
D
All ${E_c},{E_g},{E_v}$ decrease

## Explanation

A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice. The spacing between unit cells in various directions is called its lattice parameters or constants. Increasing these lattice constants will increase or widen the band-gap $\left( {Eg} \right)$, which means more energy would be required by electrons to reach the conduction band from the valence band. automatically ${E_c}$ and ${E_v}$ decreases.