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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Faraday’s Law of Induction”.

1. Which among the following is true about Faraday’s law of Induction?
a) An emf is induced in a conductor when it cuts the magnetic flux
b) An emf is induced in a conductor when it moves parallel to the magnetic field
c) An emf is induced in a conductor when it moves perpendicular to the magnetic field
d) An emf is induced in a conductor when it is just entering a magnetic field

Explanation: According to Faraday’s law of electromagnetic induction, an emf is induced in a conductor when it cuts across the flux of a magnetic field. If the two ends of the conductor are connected to an outside circuit, the induced emf causes current to flow in the circuit.

2. What is proportional to the magnitude of the induced emf in the circuit?
a) Rate of change of current in the circuit
b) Rate of change of resistance offered
c) Rate of change of magnetic flux
d) Rate of change of voltage

Explanation: The magnitude of induced emf is equal is equal to the time rate of change of magnetic flux. It is mathematically expressed as:
ε = $$\frac {-d\phi }{dt}$$
The negative sign indicates the direction of the emf induced. This is Faraday’s second law of electromagnetic induction.

3. Faraday’s laws are result of the conservation of which quantity?
a) Momentum
b) Energy
c) Charge
d) Magnetic field

Explanation: Faraday’s laws are result of the conservation of energy. These laws are based on the conversion of electrical energy into mechanical energy. Mechanical energy can be converted into electrical energy such as in the example of a dynamo. In the same way, electrical energy can be converted into mechanical energy such as in the example of electric motor. Both of the above examples work on the principle of Faraday’s law.
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4. The induced emf persists only as long as the change in magnetic flux continues.
a) True
b) False

Explanation: According to Faraday’s first law, whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in the circuit. This induced emf persists as long as he change in magnetic flux continues. Therefore, this is a true statement.

5. The magnetic flux in a closed circuit of resistance 20 Ω varies with time t as Φ = 4t3 + 2t2 – 15t + 3. Calculate the magnitude of induced emf at t = 1s.
a) 3 V
b) 4 V
c) 5 V
d) 6 V

Explanation: Given: Resistance = 20 Ω; Φ = 4t3 + 2t2 – 15t + 3
Required equation ➔ ε = $$\frac {-dΦ}{dt}$$
ε=$$\frac {-d(4t^3 + 2t^2 – 15t + 3)}{dt}$$ = -(12t2 + 4t – 15t + 3)
= -12 – 4 + 15 – 3 (Since t = 1s)
= 4 V
Therefore, the magnitude of induced emf is 4V.
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