Electromagnetic Induction Test

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Electromagnetic Induction Test - 12

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Question 1
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A constant current I is maintained in a solenoid. Which of the following quantities will not increase if an iron rod is inserted in the solenoid along its axis?

A
Magnetic field at the centre.

B
Self-inductance of the solenoid.

C
Magnetic flux linked with the solenoid.

D
Rate of joule heating.

Solution

When an iron rod is inserted inside a solenoid the magnetic field inside the solenoid increases due to the high magnetic permeability of iron. Due to the increased magnetic field, the magnetic flux also increases. The self-inductance of the solenoid also increases because self-inductance (L) of the coil is directly proportional to the permeability of the material inside the solenoid. The rate of joule heating doesn’t change.
Question 2
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Whenever the magnetic flux () linked with a coil changes the emf is induced in the circuit, This emf lasts

A
as long as the change in flux continues.

B
for a long time

C
for a short time

D
forever

Solution

The induced emf ,E=− dϕ/dt where ϕ=magnetic flux
Hence, emf will last as long as flux keeps changing.
Question 3
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The expression for the magnetic flux

A
φ = NBA² cos θ

B
φ = NBA cos θ

C
φ = N²BA cos θ

D
φ = NB²A cos θ

Solution

Magnetic Flux Formula
Magnetic flux is the product of the average magnetic field times the perpendicular area that it crosses.
Magnetic flux = number of turns x Magnetic field x Area x (angle between the planar area and the magnetic flux)
The equation is:
Φ =N B A cos(θ)
Where:
N=number of turns
Φ: Magnetic Flux
A: Area
B: Magnetic field
θ: angle between a perpendicular vector to the area and the magnetic field
Question 4
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A magnet is moved towards the coil (a) quickly and (b) slowly, and then the work done is

A
does not depend on the motion of the magnet.

B
smaller in case (a)

C
equal in both cases

D
larger in case (a)

Solution

When a magnet is moved towards the coil quickly, the rate of change of flux is larger than that if the magnetic field is moved slowly, thus larger emf is induced due to quick movement of the coil.
Question 5
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A cylindrical bar magnet is held along the axis of a circular conducting loop. Which one of the following movements of the bar magnet will not induce a current in the loop?

A
The magnet is rotated about its own axis.

B
The magnet is moved along its length.

C
The magnet is rotated about an axis passing through its mid point and perpendicular to its length.

D
The magnet is rotated about an axis through one end and perpendicular to its length.

Solution

A cylindrical bar magnet is kept along the axis of a circular coil. If the magnet is rotated about its axis, then there is no change in magnetic flux, there is no emf induced in the coil, no current will be induced in the coil.
Question 6
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The magnetic flux () linked with a coil is related to the number (N) of turns of the coil as

A

B

C

D
Question 7
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The total number of magnetic lines of force crossing a surface normally is termed as

A
Magnetic field.

B
Magnetic permeability.

C
Magnetic flux.

D
Magnetic susceptibility.

Solution

The measurement of the total magnetic field that passes through a given area is known as magnetic flux. It is helpful in describing the effects of the magnetic force on something occupying a given area.
If we consider a simple flat area A as our example and angle θ as the angle between the normal to the surface and a magnetic field vector, then the magnetic flux is given by the equation:
ϕ=BAcosΘ
Question 8
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In the given circuit the maximum deflection in the galvanometer occurs when

A
magnet is rotated inside the coil

B
magnet is stationary at the center of the coil.

C
numbers of turns in the coil is reduced.

D
magnet is pushed into the coil.

Solution

This question based on lenz law. as the bar magnet is moving , there is a change in magnetic flux.This will give polarity in the coil. Hence the current developed in the coil. so the option d is right.
Question 9
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A coil of area 10 cm² of 20 turns is placed in uniform magnetic field of 10⁴ gauss. The normal to the plane of the coil makes an angle of 60° with the magnetic field. The flux in maxwell through the coil is

A
10⁵

B
10⁶

C
10³

D
10⁴

Solution

1 gauss=10-4 Tesla
Φ=BANCos θ
Φ=10⁴x10⁴x10x10^-4x20xcos60o
=105x20x1/2
=10⁶
Question 10
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Find the flux contained by the material when the flux density is 11.7 Tesla and the area is 2 units.

A
23.4

B
12.3

C
32.4

D
21.3

Solution

The total flux is given by φ = ∫ B.ds, where ∫ds is the area. Thus φ = BA. We get φ = 11.7 x 2 = 23.4 units.