Question 1

'SI' unit of magnetic flux is

Accepted Answer

weber

Answer

gauss

Answer

ampere/meter²

Answer

orested

Question 2

A square coil of 0.01 m²area is placed perpendicular to the uniform magnetic field of 10³ weber/metre² . The magnetic flux linked with the coil is

Accepted Answer

10 weber

Answer

Zero

Answer

100 weber

Answer

10^–5 weber

Question 3

According to Faraday's Laws of electro magnetic induction:

Accepted Answer

The induced emf in the coil is proportional to the rate of change of magnetic flux associated with it

Answer

None of the above

Answer

The direction of the induced current is such that it opposes it self

Answer

The direction of induced emf is such that it opposes it self

Question 4

A coil having an area of 2 m² is placed in a magnetic field which changes from 1 Weber/m² to 4 Weber/ m²in 2 seconds. The e.m.f. induced in the coil will be :–

Accepted Answer

3 volt

Answer

2 volt

Answer

4 volt

Answer

1 volt

Question 5

Magnetic field through a coil is changed with respect to time then emf induced in it then select the incorrect regarding induced emf in coil :-

Accepted Answer

Coil must be of conducting nature

Answer

Induced emf does not depends upon resistance of the coil

Answer

Coil may be connected with an open circuit

Answer

Coil may be made up with wood

Question 6

The current flows in a circuit as shown below. If a second circuit is brought near the first circuit then the current in the second circuit will be :-

Accepted Answer

Anti clock wise

Answer

None of the above

Answer

Depending on the value of RG

Answer

Clock wise

Question 7

A coil of resistance 10 $\Omega$ and 1000 turns have the magnetic flux line of 5.5 x 10^–4 Wb. If the magnetic flux changed to 5 x 10^–4Wb. in 0.1 sec, then the induced charge in coil is :–

Accepted Answer

5 $\Omega$ C

Answer

2 $\Omega$ C

Answer

50 $\Omega$ C

Answer

20 $\Omega$ C

Question 8

One coil of resistance 40 $\Omega$ is connected to a galvanometer of 160 $\Omega$ resistance. The coil has radius 6mm and turns 100. This coil is placed between the poles of a magnet such that magnetic field is perpendicular to coil. If coil is dragged out then the charge through the galvanometer is 32 $\mu$ C. The magnetic field is:-

Accepted Answer

0.566 T

Answer

0.655 T

Answer

6.55 T

Answer

5.66 T

Question 9

A square loop of side 22 cm is changed to a circle in time 0.4 s. The magnetic field present is 0.2 T. The emf induced is :-

Accepted Answer

–6.6 mV

Answer

–13.2 mV

Answer

+6.6 mV

Answer

+13.2 mV

Question 10

The magnetic flux in a coil of 100 turns increases by 12 × 10³ Maxwell in 0.2 s due to the motion of a magnet. The emf induced in the coil will be:-

Accepted Answer

0.6 mV

Answer

60 V

Answer

0.6 V

Answer

6 V

Question 11

A closed coil consists of 500 turns on a rectangular frame of area 4.0 cm² and has a resistance of 50 ohms. The coil is kept with its plane perpendicular to a uniform magnetic field of 0.2 wb/m² , the amount of charge flowing through the coil if it is turned over (rotated through 180o ):-

Accepted Answer

1.6 × 10^–3 C

Answer

16 × 10^–3C

Answer

0.16 × 10^–3 C

Answer

160 × 10^–3 C

Question 12

A coil of mean area 500 cm² and having 1000 turns is held perpendicular to a uniform field of 0.4 gauss. The coil is turned through 180⁰ in $\mu$ second. The average induced e.m.f:-

Accepted Answer

0.04 V

Answer

0.004 V

Answer

4 V

Answer

0.4 V

Question 13

An emf induced in a coil, the linking magnetic flux

Accepted Answer

Can be either increased or decreased

Answer

Must increase

Answer

Must decrease

Answer

Must remain constant

Question 14

Consider a metal ring kept on a horizontal plane. A bar magnet is held above the ring with its length along the axis of the ring. If the magnet is dropped freely the acceleration of the falling magnet is (g is acceleration due to gravity) :-

Accepted Answer

Less than g

Answer

Depend on mass of magnet

Answer

More than g

Answer

Equal to g

Question 15

An electron beam is moving near to a conducting loop then the induced current in the loop :-

Accepted Answer

no current

Answer

anticlockwise

Answer

clockwise

Answer

both

Question 16

The current flows from A to B as shown in the figure. The direction of the induced current in the loop is :-

Accepted Answer

none of these

Answer

straight line

Answer

anticlockwise

Answer

clockwise

Question 17

Faraday law represents :-

Accepted Answer

relation between e.m.f and rate of change of flux

Answer

relation between I and B

Answer

relation between magnetic force and magnetic field

Answer

none of these

Question 18

An aluminum ring B faces an electromagnet A. The current I through A can be altered. Then which of the following statement is correct :-

Accepted Answer

If I increases, A will repel B

Answer

Whether I increases or decreases, B will not experience any force

Answer

If I decreases A will repel B

Answer

If I increases, A will attract B

Question 19

A charge particle moves along the line AB, which lies in the same plane of a circular loop of conducting wire as shown in the fig. Then :-

Accepted Answer

The current induced in the loop will change its direction as the charged particle passes by

Answer

The current induced, will be clockwise

Answer

No current will be induced in the loop

Answer

The current induced will be anticlockwise

Question 20

The magnetic flux through a circuit of resistance R changes by an amount $\Omega$ in a time $\Omega$ t. The total quantity of electric charge Q that passes any point in the circuit during the time $\mu$ t is represented by:–

Accepted Answer

Q = $\Omega$

Answer

Q = $\Omega$ . $\Omega$

Answer

Q = R . $\Omega$

Answer

Q = $\Omega$

Question 21

If number of turns of 70 cm² coil is 200 and it is placed in a magnetic field of 0·8 Wb/m² which is perpendicular to the plane of coil and it is rotated through an angle 180° in 0·1 sec, then induced emf in coil :-

Accepted Answer

22.4 V

Answer

11.2 V

Answer

1.12 V

Answer

2.24 V

Question 22

A circular loop of radius r is placed in a region where magnetic field increases with respect to time as B(t) = at then induced emf in coil :-

Accepted Answer

Answer

3<math>\pi r^2a</math>

Answer

2<math>\pi r^2a</math>

Answer

4<math>\pi r^2a</math>

Question 23

A circular loop of radius r is moved away from a current carrying wire then induced current in circular loop will be :-

Accepted Answer

Clock wise

Answer

Not induced

Answer

Anti clockwise

Answer

None of them

Question 24

When the current through a solenoid increases at a constant rate, the induced current.

Accepted Answer

is a constant and is opposite to the direction of the inducing current

Answer

increase with time and is in the direction of the inducing current

Answer

increase with time and opposite to the direction of the inducing current

Answer

is a constant and is in the direction of the inducing current

Question 25

A solenoid of 10 henry inductance and 2 ohm resistance, is connected to a 10 volt battery. In how much time the magnetic energy will reach to 1/4th of the maximum value?

Accepted Answer

3.5 sec

Answer

5.5 sec

Answer

7.5 sec

Answer

2.5 sec

Question 26

An inductance coil have the time constant 4 sec, if it is cut into two equal parts and connected parallel then new time constant of the circuit :-

Accepted Answer

4 sec

Answer

2 sec

Answer

0.5 sec

Answer

1 sec

Question 27

Which statement is correct from following –

(a) Inductor store energy in the form of magnetic field

(b) Capacitor store energy in the form of electric field

(c) Inductor store energy in the form of electric and magnetic field both

(d) Capacitor store energy in the form of electric and magnetic field both

Accepted Answer

a, b

Answer

b, d

Answer

a, c

Answer

b, c

Question 28

If a current of 2A give rise a magnetic flux of 5 × 10^–5 weber/turn through a coil having 100 turns, then the magnetic energy stored in the medium surrounding by the coil is :-

Accepted Answer

5 × 10^–3 joule

Answer

0.5 joule

Answer

5 × 10^–7 joule

Answer

5 joule

Question 29

For a solenoid keeping the turn density constant its length makes halved and its cross section radius is doubled then the inductance of the solenoid increased by :–

Accepted Answer

100%

Answer

800%

Answer

700%

Answer

200%

Question 30

A constant current i maintained in a solenoid. Which of the following quantities will increase if an iron rod is inserted in the solenoid along its axis:-

(a) Magnetic field at the centre

(b) Magnetic flux linked with the solenoid

(c) Self inductance of the solenoid

(d) Rate of Joule heating

Accepted Answer

a, b, c

Answer

a, b

Answer

c, d

Answer

Only b

Question 31

The inductance of a solenoid is 5 henry and its resistance is 5 $\Omega$ . If it is connected to a 10 volt battery then time taken by the current to reach 9/10^th of its maximum will be :-

Accepted Answer

2.3 s

Answer

4.0 s

Answer

1.2 s

Answer

1.4 s

Question 32

An LR circuit with a battery is connected at t = 0. Which of the following quantities is not zero just after the connection :-

(a) Current in circuit

(b) Magnetic potential energy in the inductor

(c) Power delivered by the battery

(d) Emf induced in the inductor

Accepted Answer

Only d

Answer

a, c

Answer

a, b

Answer

c, d

Question 33

During 0·1 s current in a coil increases from 1 A to 1·5 A. If inductance of this coil is 60 $\Omega$ H, induced current in external resistance of 600 $\Omega$ is :-

Accepted Answer

1/2 A

Answer

4/3 A

Answer

2/3 A

Answer

1 A

Question 34

In the circuit shown in figure what is the value of I₁ just after pressing the key K ?

Accepted Answer

Answer

Answer

Answer

None of the above

Question 35

Pure inductors each of inductance 3 H are connected as shown. The equivalent induction of the circuit is :-

Accepted Answer

1H

Answer

9H

Answer

2H

Answer

3H

Question 36

The time constant of an inductance coil is 2.0 × 10^–3 s. When a 90 $\Omega$ resistance is joined in series, the time constant becomes 0.5 × 10^–3 s. The inductance and resistance of the coil are :-

Accepted Answer

60 mH ; 30 $\Omega$

Answer

30 mH ; 30 $\Omega$

Answer

60 mH ; 60 $\Omega$

Answer

30 mH ; 60 $\Omega$

Question 37

A cylindrical iron core supports N turns. If a current I produces a magnetic flux $\Omega$ across the core's cross section, then the magnetic energy is :-

Accepted Answer

Answer

Answer

Answer

Question 38

The self inductance of a toroid is :-

Accepted Answer

Answer

Answer

Answer

Question 39

An inductance L and a resistance R are joined to a battery. After some time, battery is disconnected but L and R remains connected to the closed circuit. The current strength will be reduced to 37% of its initial value in :

Accepted Answer

L/R sec

Answer

R/L sec

Answer

1/LR sec

Answer

RL sec

Question 40

Energy is stored in the choke coil in the form of:-

Accepted Answer

Magnetic field

Answer

Electric field

Answer

Electro-magnetic field

Answer

Heat

Question 41

When a current changes from 2A to 4A in 0.05 sec. in a coil, induced emf is 8 V. The self inductance of coil is :-

Accepted Answer

0.2 H

Answer

0.8 H

Answer

0.4 H

Answer

0.1 H

Question 42

An e.m.f. of 12 V is induced in a given coil when the current in it changes at the rate of 48 amp./min. The inductance of the coil is :–

Accepted Answer

15 henry

Answer

0.5 henry

Answer

1.5 henry

Answer

9.6 henry

Question 43

Two conducting coils are placed co-axially now a cell is connected in one coil then they will :-

Accepted Answer

repel to each other

Answer

both (1) & (2)

Answer

attract to each other

Answer

they will not experience any force

Question 44

A coil of resistance 10 $\Omega$ and an inductance 5H is connected to a 100 volt battery. Then energy stored in the coil is :-

Accepted Answer

250 J

Answer

125 J

Answer

250 erg

Answer

125 erg

Question 45

The energy density in magnetic field B is proportional to :-

Accepted Answer

B2

Answer

Answer

Answer

B

Question 46

Inductance of a solenoid is 3H and it consist of 500 turns. If number of turn make twice, then the value of self inductance becomes:-

Accepted Answer

12 H

Answer

3 H

Answer

9 H

Answer

1.5 H

Question 47

A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is :-

Accepted Answer

5 sec

Answer

40 sec

Answer

$\pi r^2a$ sec

Answer

20 sec

Question 48

When current in a coil is reduced from 2A to 1A in 1 ms, the induced emf is 5V. The inductance of coil is :

Accepted Answer

5 mH

Answer

5000 H

Answer

50 H

Answer

5 H

Question 49

A coil of inductance 300mH and resistance 2 $\Omega$ is connected to a source of voltage 2V. The current reaches half of its steady state value in:-

Accepted Answer

0.1 s

Answer

0.15 s

Answer

0.05 s

Answer

0.3 s

Question 50

An ideal coil of 10H is connected in series with a resistance of 5 $\Omega$ and a battery of 5V.

2 seconds after the connection is made, the current flowing in amperes in the circuit is :-

Accepted Answer

(1–e^–1)

Answer

(1–e)

Answer

e

Answer

e–1

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