# NEET > Electromagnetic Induction and Alternating Currents

Explore popular questions from Electromagnetic Induction and Alternating Currents for NEET. This collection covers Electromagnetic Induction and Alternating Currents previous year NEET questions hand picked by popular teachers.

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Q 1.

Correct4

Incorrect-1

A metal disc of radius 100{tex} \mathrm { cm } {/tex} is rotated at a constant angular speed of 60{tex} \mathrm { rad } / \mathrm { s } {/tex} in a plane at right angles to an external field of magnetic induction {tex}0.05 \ \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex} . The emf induced between the centre and a point on the rim will be

A

3{tex} \mathrm { V } {/tex}

1.5{tex} \mathrm { V } {/tex}

C

6{tex} \mathrm { V } {/tex}

D

9{tex} \mathrm { V } {/tex}

##### Explanation

Q 2.

Correct4

Incorrect-1

In a coil of resistance {tex} 100 \Omega , {/tex} a current is induced by changing the magnetic flux through it as shown in the figure The magnitude of change in flux through the coil is

250{tex} \mathrm { Wb } {/tex}

B

275{tex} \mathrm { Wb } {/tex}

C

200{tex} \mathrm { Wb } {/tex}

D

225{tex} \mathrm { Wb } {/tex}

##### Explanation

Q 3.

Correct4

Incorrect-1

A 10 -meter wire is kept in east-west direction. It is falling down with a speed of 5.0 meter/second, perpendicular to the horizontal component of earth's magnetic field of {tex} 0.30 \times 10 ^ { - 4 } {/tex} weber/meter {tex} ^ { 2 } {/tex} . The momentary potential difference induced between the ends of the wire will be

0.0015{tex} \mathrm { V } {/tex}

B

0.015{tex} \mathrm { V } {/tex}

C

0.15{tex} \mathrm { V } {/tex}

D

1.5{tex} \mathrm { V } {/tex}

##### Explanation

Q 4.

Correct4

Incorrect-1

The figure shows certain wire segments joined together to form a coplanar loop. The loop is placed in a perpendicular magnetic field in the direction going into the plane of the figure. The magnitude of the field increases with time. {tex}I_{1}{/tex} and {tex}I_{2}{/tex} are the currents in the segments ab and cd. Then,

A

{tex} I _ { 1 } > I _ { 2 } {/tex}

B

{tex} I _ { 1 } < I _ { 2 } {/tex}

C

{tex} \mathrm { I } _ { 1 } {/tex} is in the direction ba and {tex} \mathrm { I } _ { 2 } {/tex} is in the direction cd

{tex} \mathrm { I } _ { 1 } {/tex} is in the direction ab and {tex} \mathrm { I } _ { 2 } {/tex} is in the direction de

##### Explanation

Q 5.

Correct4

Incorrect-1

Two solenoids of equal number of turns have their lengths and the radii in the same ratio {tex} 1 : 2 . {/tex} The ratio of their self inductances will be

{tex} 1 : 2 {/tex}

B

{tex} 2 : 1 {/tex}

C

{tex} 1 : 1 {/tex}

D

{tex} 1 : 4 {/tex}

##### Explanation

Q 6.

Correct4

Incorrect-1

A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth's magnetic field is {tex} 0.2 \times 10 ^ { - 4 } \mathrm { T } {/tex} , then the e.m.f. developed between the two ends of the conductor is

A

5{tex} \mathrm { mV } {/tex}

50{tex} \mu V {/tex}

C

5{tex} \mu \mathrm { V } {/tex}

D

50{tex} \mathrm { mV } {/tex}

##### Explanation

Q 7.

Correct4

Incorrect-1

Eddy currents do not produce

A

heat

B

a loss of energy

spark

D

damping of motion

##### Explanation

(c)

Q 8.

Correct4

Incorrect-1

A conducting square frame of side 'a' and a long staight wire carrying current I are located in the same plane as shown in the figure. The frame moves to the right with a constant velocity {tex} { 'V' } {/tex} . The emfinduced in the frame will be proportional to

A

{tex} \frac { 1 } { ( 2 x - a ) ^ { 2 } } {/tex}

B

{tex} \frac { 1 } { ( 2 x + a ) ^ { 2 } } {/tex}

{tex} \frac { 1 } { ( 2 x - a ) ( 2 x + a ) } {/tex}

D

{tex} \frac { 1 } { x ^ { 2 } } {/tex}

##### Explanation

Q 9.

Correct4

Incorrect-1

Which of the following figure correctly depicts the Lenz's law. The arrows show the movement of the labelled pole of a bar magnet into a closed circular loop and the arrows on the circle show the direction of the induced current

B

C

D

##### Explanation

Q 10.

Correct4

Incorrect-1

The magnetic flux (in weber) linked with a coil of resistance 10{tex} \Omega {/tex} is varying with respect to time {tex} t {/tex} as {tex} \phi = 4 t ^ { 2 } + 2 t + 1 . {/tex} Then the current in the coil at time {tex} t = 1 {/tex} second is

A

0.5{tex} \mathrm { A } {/tex}

B

2{tex} \mathrm { A } {/tex}

C

1.5{tex} \mathrm { A } {/tex}

1{tex} \mathrm { A } {/tex}

##### Explanation

Q 11.

Correct4

Incorrect-1

Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area A = 10 {tex}cm^{2}{/tex} and length = 20 cm. If one of the solenoid has 300 turns and the other 400 turns, their mutual inductance is {tex}(\mu_{0} = 4\pi \times 10^{-7} Tm A^{-1}{/tex})

A

{tex} 2.4 \pi \times 10 ^ { - 5 } \mathrm { H } {/tex}

B

{tex} 4.8 \pi \times 10 ^ { - 4 } \mathrm { H } {/tex}

C

{tex} 4.8 \pi \times 10 ^ { - 5 } \mathrm { H } {/tex}

{tex} 2.4 \pi \times 10 ^ { - 4 } \mathrm { H } {/tex}

##### Explanation

Q 12.

Correct4

Incorrect-1

When the current changes from {tex} + 2 \mathrm { A } {/tex} to {tex} - 2 \mathrm { A } {/tex} in 0.05 second, an e.m.f. of 8{tex} \mathrm { V } {/tex} is induced in a coil. The coefficient of self- induction of the coil is

A

0.2{tex} \mathrm { H } {/tex}

B

0.4{tex} \mathrm { H } {/tex}

C

0.8{tex} \mathrm { H } {/tex}

0.1{tex} \mathrm { H } {/tex}

##### Explanation

Q 13.

Correct4

Incorrect-1

A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux linked with each turn of the solenoid is {tex} 4 \times 10 ^ { - 3 } {/tex} Wb. The self-inductance of the solenoid is

A

2.5 henry

B

2.0 henry

1.0 henry

D

40 henry

##### Explanation

Q 14.

Correct4

Incorrect-1

A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field perpendicular to its plane as shown in figure. An electric field is induced

A

in AD, but not in BC

B

in BC but not in AD

C

neither in AD nor in BC

##### Explanation

Q 15.

Correct4

Incorrect-1

In an AC generator, a coil with N turms, all of the same area A and total resistance R, rotates with frequency in a magnetic field B. The maximum value of emf generated in the coil is

A

{tex}N.A.B.R. \omega{/tex}

B

{tex} \mathrm { N } . \mathrm { A } . \mathrm { B } {/tex}

C

{tex} \mathrm { N } . \mathrm { A } . \mathrm { B } {/tex}{tex} . \mathrm { R } {/tex}

{tex}N.A.B.\omega{/tex}

##### Explanation

Q 16.

Correct4

Incorrect-1

In an inductor of self-inductance {tex} \mathrm { L } = 2 \mathrm { mH } , {/tex} current changes with time according to relation {tex} \mathrm { i } = \mathrm { t } ^ { 2 } \mathrm { e } ^ { - \mathrm { t } } . {/tex} At what time emfis zero?

A

4{tex} \mathrm { s } {/tex}

B

3{tex} \mathrm { s } {/tex}

2{tex} \mathrm { s } {/tex}

D

1{tex} \mathrm { s } {/tex}

##### Explanation

Q 17.

Correct4

Incorrect-1

Choke coil works on the principle of

A

transient current

self induction

C

mutual induction

D

wattless current

##### Explanation

Q 18.

Correct4

Incorrect-1

A coil having n turns and resistance {tex} \mathrm { R } \Omega {/tex} is connected with a galvanometer of resistance {tex} 4 \mathrm { R } \Omega . {/tex} This combination is moved in time {tex} \mathrm { t } {/tex} seconds from a magnetic field {tex} \mathrm { W } _ { 1 } {/tex} weber to {tex} \mathrm { W } _ { 2 } {/tex} weber. The induced current in the circuit is

A

{tex} - \frac { \left( \mathrm { W } _ { 1 } - \mathrm { W } _ { 2 } \right) } { \mathrm { Rnt } } {/tex}

{tex} - \frac { \mathrm { n } \left( \mathrm { W } _ { 2 } - \mathrm { W } _ { 1 } \right) } { 5 \mathrm { Rt } } {/tex}

C

{tex} - \frac { \left( \mathrm { W } _ { 2 } - \mathrm { W } _ { 1 } \right) } { 5 \mathrm { Rnt } } {/tex}

D

{tex} - \frac { n \left( W _ { 2 } - W _ { 1 } \right) } { R _ { 1 } } {/tex}

##### Explanation

Q 19.

Correct4

Incorrect-1

A thin circular ring of area {tex} A {/tex} is held perpendicular to a uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across the ends such that the total resistance of the circuit is {tex} R {/tex} . When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is

A

{tex} \frac { B R } { A } {/tex}

{tex} \frac { \mathrm { AB } } { \mathrm { R } } {/tex}

C

ABR

D

{tex} \frac { B ^ { 2 } A } { R ^ { 2 } } {/tex}

##### Explanation

Q 20.

Correct4

Incorrect-1

A boat is moving due east in a region where the earth's magnetic field is {tex} 5.0 \times 10 ^ { - 5 } \mathrm { NA } ^ { - 1 } \mathrm { m } ^ { - 1 } {/tex} due north and horizontal. The boat carries a vertical aerial 2{tex} \mathrm { m } {/tex} long. If the speed of the boat is 1.50{tex} \mathrm { ms } ^ { - 1 } {/tex} , the magnitude of the induced emf in the wire of aerial is:

A

0.75{tex} \mathrm { mV } {/tex}

B

0.50{tex} \mathrm { mV } {/tex}

0.15{tex} \mathrm { mV } {/tex}

D

1{tex} \mathrm { mV } {/tex}

##### Explanation

Q 21.

Correct4

Incorrect-1

In a coil of area 10{tex} \mathrm { cm } ^ { 2 } {/tex} and 10 turns with magnetic field directed perpendicular to the plane and is changing at the rate of {tex} 10 ^ { 8 } {/tex} Gauss/second. The resistance of the coil is 20{tex} \Omega {/tex} . The current in the coil will be

A

0.5{tex} \mathrm { A } {/tex}

5{tex} \mathrm { A } {/tex}

C

50{tex} \mathrm { A } {/tex}

D

{tex} 5 \times 10 ^ { 8 } \mathrm { A } {/tex}

##### Explanation

Q 22.

Correct4

Incorrect-1

A horizontal straight wire 20{tex} \mathrm { m } {/tex} long extending from east to west falling with a speed of 5.0{tex} \mathrm { m } / \mathrm { s } {/tex} , at right angles to the horizontal component of the earth's magnetic field {tex} 0.30 \times 10 ^ { - 4 } \mathrm { Wb } / \mathrm { m } ^ { 2 } {/tex} . The instantaneous value of the e.m.f. induced in the wire will be

3{tex} \mathrm { mV } {/tex}

B

4.5{tex} \mathrm { mV } {/tex}

C

1.5{tex} \mathrm { mV } {/tex}

D

{tex}6 \mathrm { mV } {/tex}

##### Explanation

(a)3 mv

Q 23.

Correct4

Incorrect-1

The self inductance of a long solenoid cannot be increased by

A

increasing its area of cross section

B

increasing its length

C

changing the medium with greater permeability

increasing the current through it

##### Explanation

Q 24.

Correct4

Incorrect-1

A metallic rod of length ‘l’ is tied to a string of length 2l and made to rotate with angular speed w on a horizontal table with one end of the string fixed. If there is a vertical magnetic field ‘B’ in the region, the e.m.f. induced across the ends of the rod is

A

{tex} \frac { 2 B \omega \ell ^ { 2 } } { 2 } {/tex}

B

{tex} \frac { 3 B \omega \ell ^ { 2 } } { 2 } {/tex}

C

{tex} \frac { 4 B \omega \ell ^ { 2 } } { 2 } {/tex}

{tex} \frac { 5 B \omega \ell ^ { 2 } } { 2 } {/tex}

##### Explanation

Q 25.

Correct4

Incorrect-1

Lenz's law gives

A

the magnitude of the induced e.m.f.

the direction of the induced current

C

both the magnitude and direction of the induced current

D

the magnitude of the induced current