Electromagnetic Induction Test

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Electromagnetic Induction Test - 8

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Weekly Quiz Competition

Question 1
4 / -1

The magnetic flux passing normally through a coil is ø = 20 cos πt + t² + 50t + 25m Wb What will be the induced emf at t = 1s?

A
100 π mV

B
52 mV

C
72m V

D
(100 π + 50) mV

Solution

θ=20cos5πt+t²+50t+25 mWb
We know that,
Emf=dθ/dt=-20x5πsin5πt+2t+50+0
At,t=1
Emf=-100πsing5π+2+50
=0+2+50
=52V
Question 2
4 / -1

A copper rod moves parallel to the horizontal direction. The induced emf developed across its ends due earth’s magnetic field will be maximum at the

A
latitude 60°

B
latitude 30°

C
equator

D
poles

Solution

At the poles of the copper rod, the earth’s magnetic field will be more. This is explained with the help of Lorentz force where he explains that the magnetic field is generated due to the movement of charges.

Earth’s magnetic field is defined as the magnetic dipole which is similar to bar magnet and is tilted 11° from the earth’s axis of rotation.
Question 3
4 / -1

The magnetic flux through a surface varies with time as follows:
= 12t² + 7t + 3
here, is in milliweber and t is in seconds.
What will be the induced emf at t = 5s?

A
338 mV

B
127 mV

C
105 mV

D
None of the above

Solution

Given :
ϕ=12t²+7t+C
where, C is a constant, t is in sec, ϕ in milli-weber
The induced e.m.f. in the loop at t=5, on differentiating the equation with respect to 't'.
dtdϕ=dtd(12t²+7t+C)
=24t+7
at t=5
dtdϕ=24×(5)+7
=120+7
=127 mV
Question 4
4 / -1

In Faraday’s experiment if the magnet is moved towards the coil, it results in ____________ in magnetic field B at any point on the wire loop. The _________ shows deflection. Thus emf is induced by changing B.

A
Decrease, galvanometer

B
Increase, ammeter

C
Increase, galvanometer

D
Decrease, ammeter
Question 5
4 / -1

What is the value of induced e.m.f if a wire is moved between the gap of two poles of a magnetin in 1 s and magnetic flux between the poles is 6 x 10^-3 Wb?

A
0.6 mV

B
6 mV

C
66 mV

D
60 mV
Question 6
4 / -1

Two similar circular co-axial loops carry equal current in the same direction. If the loops be brought nearer, the currents in them will

A
Change direction

B
Decrease

C
Increase

D
Remain same

Solution

When the two loops are brought together, the flux linking the two loops increases. By Lenz's law a current will be induced such that it opposes this change of flux . Therefore to oppose the increase in flux, the current in the two loops will decrease, so the flux decreases.
Question 7
4 / -1

When a wire loop is rotated in a magnetic field, the direction of induced emf changes once in each

A
2 revolutions

B
1 revolution

C
1/2 revolution

D
12 revolution

Solution

Flux of the magnetic field through the loop
ϕ=B.Acosωt
Emf= −dϕ/dt=B.Aωsinωt
ωt=0 to π, sinωt=+ve
ωt=π to2 π, sinωt=−ve
Hence, the direction of induced e.m.f. changes once in 1/2 revolution.
Question 8
4 / -1

The induced e.m.f in a coil is given by ε = 100sin 100π volts. Calculate the number of rotations the coil makes per second.

A
100 rps

B
5 rps

C
15 rps

D
50 rps

Solution

ε=100sinπV
ε=ε0sinωt
ω=100π
2πn=100π
n=50rps
Question 9
4 / -1

The motional emf produced across a wire moving through a magnetic field does not depend on its:

A
orientation

B
velocity

C
diameter

D
length

Solution

Motional emf= Bℓv
It depends on magnetic field intensity, length and velocity. The diameter doesn't affect any of the factors.
Question 10
4 / -1

If we keep two similar loops made up of copper and constantan in a magnetic field for same amount of time, in which loop the induced e.m.f will be greater.

A
Constantan Loop

B
E.m.f won’t be induced in any of the loops

C
Copper Loop

D
Equal in both the loops

Solution

As the copper has high electrical conductivity. Hence, higher e.m.f would be induced in the copper loop.

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Electromagnetic Induction Test - 8

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Electromagnetic Induction Test - 8

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Question 1

100 π mV

52 mV

72m V

(100 π + 50) mV

Solution

Question 2

latitude 60°

latitude 30°

equator

poles

Solution

Question 3

338 mV

127 mV

105 mV

None of the above

Solution

Question 4

Decrease, galvanometer

Increase, ammeter

Increase, galvanometer

Decrease, ammeter

Question 5

0.6 mV

6 mV

66 mV

60 mV

Question 6

Change direction

Decrease

Increase

Remain same

Solution

Question 7

2 revolutions

1 revolution

1/2 revolution

12 revolution

Solution

Question 8

100 rps

5 rps

15 rps

50 rps

Solution

Question 9

orientation

velocity

diameter

length

Solution

Question 10

Constantan Loop

E.m.f won’t be induced in any of the loops

Copper Loop

Equal in both the loops

Solution

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