When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

A circular coil with a cross-sectional area of 4 cm² has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm². The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

(a)

7.54 μH

(b)

8.54 μH

(c)

9.54 μH

(d)

10.54 μH

In a series RL circuit, the resistance and inductive reactance are the same. Then the phase difference between the voltage and current in the circuit is

(a)

\(\frac{\pi}{4}\)

(b)

\(\frac{\pi}{2}\)

(c)

\(\frac{\pi}{6}\)

(d)

zero

An inductor 20 mH, a capacitor 50 μF and a resistor 40Ω are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is

(a)

0.76 W

(b)

0.89 W

(c)

0.46 W

(d)

0.67 W

Lenz's law is in accordance with the law of ________________.

(a)

conservation of charges

(b)

conservation of flux

(c)

conservation of momentum

(d)

conservation of energy

The self-inductance of a straight conductor is ________________.

(a)

zero

(b)

infinity

(c)

very large

(d)

very small

An emf of 12V is induced when the current in the coil changes at the rate of 40 A S^-1. The coefficient of self-induction of the coil is _______________.

(a)

0.3 H

(b)

0.003 H

(c)

30 H

(d)

4.8 H

Which of the following cannot be stepped up in a transformer?

(a)

input current

(b)

input voltage

(c)

input power

(d)

all

If a secondary coil has 40 turns, and a primary coil with 20 turns is charged with 50V of potential difference, then potential difference in secondary would be ________________.

(a)

50 V

(b)

25 V

(c)

60 V

(d)

100 V

The unit of self inductance is ________________.

(a)

Henry

(b)

Ampere

(c)

Farad

(d)

Ohm

A phenomenon in which a varying current in one coil induces an emf in the neighbouring coil is ___________.

(a)

mutual induction

(b)

self induction

(c)

electrostatic induction

(d)

electromagnetic induction

The property of a coil which enables to produce an opposite induced emf in it when the current in the coil changes is called _______________

(a)

electromagnetism

(b)

self - induction

(c)

mutual induction

(d)

parallel- induction

In an a.c generator, the brushes are made of __________

(a)

silicon

(b)

plastic

(c)

carbon

(d)

nylon

In an a.c. dynamo, the induced current is _________ in nature.

(a)

alternating

(b)

increasing

(c)

decreasing

(d)

constant

__________ principle is used in transformer.

(a)

mutual induction

(b)

electromagnetic induction

(c)

self induction

(d)

eddy currents

The efficiency of an ideal transformer is ____________.

(a)

0

(b)

1

(c)

infinite

(d)

none

The voltage drop across the resistor in a LCR series circuit is __________________

(a)

V_R = IR

(b)

V_R = IR₂

(c)

V_R = I/R

(d)

V_R=R/I

Unit of inductive reactance is ___________

(a)

ohm-metre

(b)

mho-metre^-1

(c)

ohm

(d)

mho

The power factor of an a.c, circuit is _________

(a)

\(\phi \)sin\(\phi \)

(b)

cosec \(\phi \)

(c)

cos \(\phi \)

(d)

tan \(\phi \)

The instantaneous current in an AC circuit containing a pure inductor is i = I_o sinωt, The instantaneous emf is ___________________.

(a)

e = E_osin\(\left( \omega t+\frac { \pi }{ 2 } \right) \)

(b)

e = E_osin\(\left( \omega t-\frac { \pi }{ 2 } \right) \)

(c)

e=E_osin(ωt - π)

(d)

e = E_osin