 JEE Mains Previous Years Questions with Solutions

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1

AIEEE 2004

A coil having $n$ turns and resistance $R\Omega$ is connected with a galvanometer of resistance $4R\Omega .$ This combination is moved in time $t$ seconds from a magnetic field ${W_1}$ weber to ${W_2}$ weber. The induced current in the circuit is
A
${{\left( {{W_2} - {W_1}} \right)} \over {Rnt}}$
B
$- {{n\left( {{W_2} - {W_1}} \right)} \over {5\,\,Rt}}$
C
$- {{\left( {{W_2} - {W_1}} \right)} \over {5\,\,Rnt}}$
D
$- {{n\left( {{W_2} - {W_1}} \right)} \over {Rt}}$

Explanation

${{\Delta \phi } \over {\Delta t}} = {{\left( {{W_2} - {W_1}} \right)} \over t}$

${R_{tot}} = \left( {R + 4R} \right)\Omega = 5R\Omega$

$i = {{nd\phi } \over {{R_{tot}}dt}} = {{ - n\left( {{W_2} - {W_1}} \right)} \over {5Rt}}$

( as ${W_2}\,\,\& \,\,{W_1}$ are magnetic flux )
2

AIEEE 2004

In an $LCR$ series $a.c.$ circuit, the voltage across each of the components, $L,C$ and $R$ is $50V$. The voltage across the $L.C$ combination will be
A
$100V$
B
$50\sqrt 2$
C
$50$ $V$
D
$0$ $V$ (zero)

Explanation

Since the phase difference between $L$ & $C$ is $\pi ,$

$\therefore$ net voltage difference across $LC=50-50=0$
3

AIEEE 2004

Alternating current can not be measured by $D.C.$ ammeter because
A
Average value of current for complete cycle is zero
B
$A.C.$ Changes direction
C
$A.C.$ can not pass through $D.C.$ Ammeter
D
$D.C.$ Ammeter will get damaged.

Explanation

$D.C.$ ammeter measure average current in $AC$ current, average current is zero for complete cycle. Hence reading will be zero.
4

AIEEE 2003

The core of any transformer is laminated so as to
A
reduce the energy loss due to eddy currents
B
make it light weight
C
make it robust and strong
D
increase the secondary voltage

Explanation

Laminated core provide less area of cross-section for the current to flow. Because of this, resistance of the core increases and current decreases thereby decreasing the eddy current losses.