### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2006

In a Wheatstone's bridge, three resistance $P, Q$ and $R$ connected in the three arms and the fourth arm is formed by two resistances ${S_1}$ and ${S_2}$ connected in parallel. The condition for the bridge to be balanced will be
A
${P \over Q} = {{2R} \over {{S_1} + {S_2}}}$
B
${P \over Q} = {{R\left( {{S_1} + {S_2}} \right)} \over {{S_1}{S_2}}}$
C
${P \over Q} = {{R\left( {{S_1} + {S_2}} \right)} \over {2{S_1}{S_2}}}$
D
${P \over Q} = {R \over {{S_1} + {S_2}}}$

## Explanation

${P \over Q} = {R \over S}$ where $S = {{{S_1}{S_2}} \over {{S_1} + {S_2}}}$
2

### AIEEE 2006

An electric bulb is rated $220$ volt - $100$ watt. The power consumed by it when operated on $110$ volt will be
A
$75$ watt
B
$40$ watt
C
$25$ Watt
D
$50$ Watt

## Explanation

The resistance of the bulb is $R = {{{V^2}} \over P} = {{{{\left( {220} \right)}^2}} \over {100}}$

The power consumed when operated at $110$ $V$ is

$P = {{{{\left( {110} \right)}^2}} \over {{{\left( {220} \right)}^2}/100}} = {{100} \over 4} = 25\,W$
3

### AIEEE 2006

A thermocouple is made from two metals, Antimony and Bismuth. If one junction of the couple is kept hot and the other is kept cold, then, an electric current will
A
flow from Antimony to Bismuth at the hot junction
B
flow from Bismuth to Antimony at the cold junction
C
now flow through the thermocouple
D
flow from Antimony to Bismuth at the cold junction

## Explanation

At cold junction, current flows from Antimony to Bismuth (because current flows from metal occurring later in the series to metal occurring earlier in the thermoelectric series).
4

### AIEEE 2005

An energy source will supply a constant current into the load if its internal resistance is
A
very large as compared to the load resistance
B
equal to the resistance of the load
C
non-zero but less than the resistance of the load
D
zero

## Explanation

$I = {E \over {R + r}},\,$ Internal resistance $\left( r \right)$ is

zero, $I = {E \over R} =$ constant.