### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2002

In a transformer, number of turns in the primary coil are $140$ and that in the secondary coil are $280.$ If current in primary coil is $4A,$ then that in the secondary coil is
A
$4A$
B
$2A$
C
$6A$
D
$10A$

## Explanation

${N_p} = 140,\,\,{N_s} = 280,\,\,{I_p} = 4A,\,\,{I_s} = ?$

For a transformer ${{{I_s}} \over {{I_p}}} = {{{N_p}} \over {{N_s}}}$

$\Rightarrow {{{I_s}} \over 4} = {{140} \over {280}} \Rightarrow {I_s} = 2A$
2

### AIEEE 2002

The power factor of $AC$ circuit having resistance $(R)$ and inductance $(L)$ connected in series and an angular velocity $\omega$ is
A
$R/\omega L$
B
$R/{\left( {{R^2} + {\omega ^2}{L^2}} \right)^{1/2}}$
C
$\omega L/R$
D
$R/{\left( {{R^2} - {\omega ^2}{L^2}} \right)^{1/2}}$

## Explanation

The impedance triangle for resistance $\left( R \right)$ and inductor $(L)$ connected in series is shown in the figure.

Power factor $\cos \phi = {R \over {\sqrt {{R^2} + {\omega ^2}{L^2}} }}$