# Topic: Electromagnetic Induction (Test 1)

Topic: Electromagnetic Induction
Q.1
electromagnetic induction i.e currents can be induced in coils (Select the best)
A. Only if the magnet moves
B. Only if the coil moves
C. if relative motion of coil and magnet is present.
D. Only if the coil moves and magnet also moves in the same direction
Explaination / Solution:

for electromagnetic induction magnet and coil both may move but relative motion between must be present

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Q.2
When a bar magnet is pushed towards the coil connected in series with a galvanometer, the pointer in the galvanometer G
A. shows deflection while bar is stationary
B. shows deflection while bar is in motion
C. oscillates
D. does not move
Explaination / Solution:

When bar is in motion then flux will changed hence current will be induced.

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Q.3

When current carrying coil  is moved towards the coil  connected in series with a galvanometer, the pointer in the galvanometer G

A. shows deflection while  is stationary
B.
oscillates

C. shows deflection while  is stationary motion
D.
does not move

Explaination / Solution:

current induced due to flux changed when C2 is in motion .

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Q.4
Coils  and  are stationary.  connected in series with a galvanometer while  is connected to a battery through a tapping key. If the tapping key is pressed and released the galvaometer
A. shows deflection while  is stationary
B. does not move
C. shows deflection while current inis changing
D.
oscillates

Explaination / Solution:

flux will be changed when current in C2 is changing. Hence current will be induced in coil C1.

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Q.5
Magnetic flux (ΦB) through a surface S is given by
A. μ0B⃗ .ds
B. B⃗ .ds
C. B⃗ ×ds
D. B⃗ .ds
Explaination / Solution:

if dS is area of an element of any arbitrary shape and magnetic field at this element is B. The total magnetic flux through the surface is the sum of the contributions from the individual area elements.

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Q.6
A. The magnitude of the induced emf in a circuit is proportional to the time of change of magnetic flux through the circuit.
B. The magnitude of the induced emf in a circuit is equal to the time of change of magnetic flux through the circuit.
C. The magnitude of the induced emf in a circuit is equal to change of magnetic flux through the circuit.
D. The magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit. .
Explaination / Solution:

The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit.

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Q.7
According to Farady's law for a coil having N turns, the total induced emf is given by
A. e=μ0NdϕBdt
B. e=μ0N2dϕBdt
C. e=dϕBdte=−NdϕBdt
D. e=dϕBdt
Explaination / Solution:

The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit.

induced emf for a coil having 1 turns will be

The flux of all the turns will be added up. So the induced emf for a coil having N turns will be

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Q.8
Coils  and  are stationary.  connected in series with one very small diwali bulb while  is connected to a battery .If the connection is suddenly snapped
A. the bulb absorbs light
B. nothing happens to the bulb
C. the bulb keeps glowing
D. the bulb glows momentarily.
Explaination / Solution:

Flux will be changed due to this current is induced momentarily

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Q.9
According to Lenz’s law
A. The induced emf is proportional change in magnetic flux that produced it.
B. The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it. .
C. The induced emf is proportional rate of change in magnetic flux that produced it.
D. The polarity of induced emf is such that it tends to produce a current which aids the change in magnetic flux that produced it.
Explaination / Solution:

Direction of an induced emf, or the current, in any circuit is such as to oppose the cause that produce it. If the direction of the induced current were such as not to oppose then we would be obtaining electrical energy continuously without doing work, which is impossible

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Q.10
If the polarity of induced emf is such that it tends to produce a current which aids the change in magnetic flux that produced it, which conservation law is violated?
A. conservation of mass
B. conservation of charge
C. conservation of energy.
D. conservation of momentum