Electromagnetic Induction Test

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Electromagnetic Induction Test - 15

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Question 1
1 / -0

A magnet is moved towards the coil (i) quickly, (ii) slowly, the induced emf is

A
more in (i) than in (ii) case.

B
Smaller in (i) than in (ii) case.

C
Same in both.

D
Nothing can be said.

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 2
1 / -0

The magnetic flux linked with a coil is changed from 1 Wb to 0.1 Wb in 0.1 second. The induced emf is

A
0.9V

B
0.09V

C
9.0V

D
0.009V

Solution

Change n in magnetic flux Δϕ=0.1−1=−0.9 Weber
Time taken Δt=0.1 sec
So, emf induced in the coil E=− Δϕ/Δt
⟹ E=− (−0.9)/ 0.1=9 Volts
Hence option C is the correct answer.
Question 3
1 / -0

The principle of electromagnetic induction is used in which of the following phenomenon

A
Generation of electricity in hydroelectricity.

B
Generation of electricity in nuclear power plant.

C
Generation of electricity in thermal power plant.

D
Generation of electricity from wind energy.

Solution

In hydroelectricity the power of a turbine depends on the size of the water drop and the quantity of water flowing through the turbine. The water propels the turbine, which in turn powers an electric generator, which produces electricity under the principle of electromagnetic induction.
Question 4
1 / -0

Which of the following law’s gives the direction of induced emf?

A
Lenz’s law

B
Ampere’s circuital law

C
Faraday’s law

D
Biot Savart law
Solution
Lenz’s law is used for determining the direction of induced current.
Lenz’s law of electromagnetic induction states that the direction of induced current in a given magnetic field is such that it opposes the induced change by changing the magnetic field.
Following is the formula of Lenz’s law:
ϵ=−N (∂ϕ_B/∂t)
Where,
ε is the induced emf
∂ΦB is the change in magnetic flux
N is the number of turns in the coil

Lenz’s law finds application in electromagnetic braking and in electric generators
Question 5
1 / -0

In the expression, what is the significance of negative sign?

A
The induced emf is always opposite to the direction of flux.

B
The induced emf decreases when there is change in the magnetic flux.

C
The induced emf is produced only when the magnetic flux decreases.

D
The induced emf opposes the changes in the magnetic flux.

Solution

The negative sign signifies that the induced emf always opposes any change in the magnetic flux.
Question 6
1 / -0

Magnetic flux φ in Weber in closed circuit of resistance 15 ohm varies with time t sec as φ = 2t² – 3t + 1. The magnitude of induced emf at t = 0.25 sec is

A
4V

B
2V

C
8V

D
6V

Solution

= 4t-3
At t = 0.25s
e= 2V
Question 7
1 / -0

If the North Pole of the bar magnet is introduced into a coil at the end A which of the following statements correctly depicts the phenomenon taking place.

A
The end A of the coil acquires positive potential.

B
The end A of the coil behaves like a north pole.

C
The end A of the coil behaves like a south pole.

D
The end A of the coil acquires negative potential.

Solution

According to Lenz’s law the end A becomes the North Pole to oppose the motion of the magnet.
Hence, option B is correct.
Question 8
1 / -0

In which of the following cases with a bar magnet and the coil no induced emf is induced.

A
When there is no relative motion between the magnet and the coil.

B
When the coil is moved towards or away from the magnet.

C
When the magnet is taken away from the coil.

D
When the magnet is inserted into the coil.

Solution

This is because induced emf directly depends on relative motion between the magnet and coil, but if there is no relative motion between them, there will be no emf induced.
Question 9
1 / -0

The role of inductance is equivalent to:

A
energy

B
force

C
inertia

D
momentum

Solution

Self induction is that phenomenon in which a change in electric current in a coil produces an induced emf in the coil itself.
Now, it is also known as inertia of electricity as for if we were to change electric current through a current carrying coil it will tend to oppose any further change in its emf. This is similar to inertial behavior in mechanics where bodies in either rest or motion tend to oppose any change in their state. Here mass is the inertial property analogous to self inductance.
Question 10
1 / -0

A coil of 100 turns is pulled in 0.04 sec. between the poles of a magnet, if its flux changes from 40 x 10^-6 Wb per turn to 10^-5 Wb per turn, then the average emf induced in the coil is

A
0.75V

B
7.5V

C
0.0075V

D
0.075V

Solution

Emf = - N(∆magnetic flux)/∆t
N=100turns
∆magnetic flux= -30×10-6Wb
∆t = 0.04sec
Emf = -(100turns)(-30×10-6)/(0.04sec)
Emf = 0.075V

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Electromagnetic Induction Test - 15

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Question 1

more in (i) than in (ii) case.

Smaller in (i) than in (ii) case.

Same in both.

Nothing can be said.

Solution

Question 2

0.9V

0.09V

9.0V

0.009V

Solution

Question 3

Generation of electricity in hydroelectricity.

Generation of electricity in nuclear power plant.

Generation of electricity in thermal power plant.

Generation of electricity from wind energy.

Solution

Question 4

Lenz’s law

Ampere’s circuital law

Faraday’s law

Biot Savart law

Solution

Question 5

The induced emf is always opposite to the direction of flux.

The induced emf decreases when there is change in the magnetic flux.

The induced emf is produced only when the magnetic flux decreases.

The induced emf opposes the changes in the magnetic flux.

Solution

Question 6

4V

2V

8V

6V

Solution

Question 7

The end A of the coil acquires positive potential.

The end A of the coil behaves like a north pole.

The end A of the coil behaves like a south pole.

The end A of the coil acquires negative potential.

Solution

Question 8

When there is no relative motion between the magnet and the coil.

When the coil is moved towards or away from the magnet.

When the magnet is taken away from the coil.

When the magnet is inserted into the coil.

Solution

Question 9

energy

force

inertia

momentum

Solution

Question 10

0.75V

7.5V

0.0075V

0.075V

Solution

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