Q.1 Who discovered electromagnetic induction?
Michael Faraday
James Clerk Maxwell
Albert Einstein
André-Marie Ampère
Explanation - Michael Faraday discovered electromagnetic induction in 1831, demonstrating that a changing magnetic field induces an electric current in a conductor.
Correct answer is: Michael Faraday
Q.2 Which law explains the direction of induced current?
Faraday's Law
Lenz's Law
Ohm's Law
Coulomb's Law
Explanation - Lenz's Law states that the induced current flows in a direction such that its magnetic field opposes the change in magnetic flux that produced it.
Correct answer is: Lenz's Law
Q.3 The SI unit of magnetic flux is:
Tesla
Weber
Henry
Gauss
Explanation - Magnetic flux is measured in Weber (Wb). One Weber equals one Tesla·m².
Correct answer is: Weber
Q.4 If a coil has 200 turns and the magnetic flux changes at 0.05 Wb/s, the induced EMF is:
5 V
10 V
2 V
0.01 V
Explanation - Faraday's law: EMF = -N(dΦ/dt) = 200 * 0.05 = 10 V.
Correct answer is: 10 V
Q.5 Self-inductance of a coil is defined as:
Induced EMF in another coil due to change in current
EMF induced in the coil due to its own changing current
Magnetic flux per unit area
Resistance per unit length
Explanation - Self-inductance is the property of a coil that induces an EMF in itself when its current changes.
Correct answer is: EMF induced in the coil due to its own changing current
Q.6 The unit of inductance is:
Weber
Henry
Tesla
Ampere
Explanation - Inductance is measured in Henry (H), where 1 H = 1 Wb/A.
Correct answer is: Henry
Q.7 Mutual induction occurs when:
A coil induces EMF in itself
A changing current in one coil induces EMF in another nearby coil
Magnetic flux is constant
A conductor moves in a uniform magnetic field
Explanation - Mutual induction refers to the induction of EMF in one coil due to the change in current in a nearby coil.
Correct answer is: A changing current in one coil induces EMF in another nearby coil
Q.8 A metal rod of length 0.5 m moves with a speed of 2 m/s perpendicular to a 1 T magnetic field. The induced EMF is:
1 V
0.5 V
2 V
4 V
Explanation - EMF = B * L * v = 1 * 0.5 * 2 = 1 V.
Correct answer is: 1 V
Q.9 The negative sign in Faraday’s law indicates:
Energy loss
Direction of induced EMF
Magnitude of flux
Resistance of coil
Explanation - The negative sign represents Lenz's Law, indicating that the induced EMF opposes the change in magnetic flux.
Correct answer is: Direction of induced EMF
Q.10 A solenoid has 500 turns and carries a current increasing at 0.2 A/s. If its self-inductance is 0.1 H, the induced EMF is:
0.02 V
0.2 V
0.5 V
1 V
Explanation - EMF = L * (di/dt) = 0.1 * 0.2 = 0.02 V.
Correct answer is: 0.02 V
Q.11 Eddy currents are:
Currents in a wire coil
Induced currents in a bulk conductor opposing flux change
Electric currents due to batteries
Ion currents in gases
Explanation - Eddy currents are loops of induced currents circulating within conductors, creating magnetic fields that oppose the change in flux.
Correct answer is: Induced currents in a bulk conductor opposing flux change
Q.12 To reduce eddy current losses in transformers, cores are made of:
Solid iron
Copper
Laminated iron
Aluminum
Explanation - Laminated cores reduce the path for eddy currents, minimizing losses.
Correct answer is: Laminated iron
Q.13 A circular coil of radius 0.1 m is in a magnetic field of 0.5 T. If the magnetic flux through the coil changes from 0 to 0.015 Wb in 0.01 s, the induced EMF is:
1.5 V
1.0 V
0.5 V
0.15 V
Explanation - EMF = ΔΦ / Δt = 0.015 / 0.01 = 1.5 V.
Correct answer is: 1.5 V
Q.14 Which factor does NOT affect the magnitude of induced EMF in a coil?
Number of turns
Rate of change of flux
Resistance of the coil
Area of the coil
Explanation - Induced EMF depends on flux change, coil turns, and area, not on resistance, which affects current.
Correct answer is: Resistance of the coil
Q.15 A transformer works on the principle of:
Electrostatic induction
Mutual induction
Eddy currents
Lenz's Law only
Explanation - Transformers transfer energy from one coil to another through mutual induction.
Correct answer is: Mutual induction
Q.16 The induced EMF in a straight conductor moving through a magnetic field is maximum when:
Conductor is parallel to the field
Conductor is perpendicular to the field
Conductor is at 45° to the field
Velocity is zero
Explanation - EMF is given by E = B L v sinθ, maximum when θ = 90°.
Correct answer is: Conductor is perpendicular to the field
Q.17 Which of the following is true for a perfect inductor in AC circuit?
Voltage and current are in phase
Voltage leads current by 90°
Current leads voltage by 90°
Voltage and current are zero
Explanation - In an ideal inductor, the voltage across it leads the current by 90° in AC circuits.
Correct answer is: Voltage leads current by 90°
Q.18 Faraday's law of induction is a consequence of:
Conservation of energy
Newton's law
Coulomb's law
Ohm's law
Explanation - The induced EMF produces current in a direction to oppose the change, ensuring energy conservation.
Correct answer is: Conservation of energy
Q.19 In a moving coil galvanometer, the coil experiences torque due to:
Induced current in external circuit
Interaction of current with magnetic field
External mechanical force
Gravitational force
Explanation - The current-carrying coil in a magnetic field experiences a torque, causing deflection.
Correct answer is: Interaction of current with magnetic field
Q.20 A coil is rotated in a magnetic field. The maximum EMF is induced when:
Plane of coil is perpendicular to field
Plane of coil is parallel to field
Rotation is slow
Number of turns is minimal
Explanation - Maximum flux change occurs when the plane of the coil is perpendicular to the field, inducing maximum EMF.
Correct answer is: Plane of coil is perpendicular to field
Q.21 Induced EMF is zero when:
Flux is constant
Flux is increasing
Flux is decreasing
Conductor is moving
Explanation - No change in magnetic flux means no induced EMF according to Faraday’s law.
Correct answer is: Flux is constant
Q.22 In a transformer, if the secondary voltage is higher than the primary, it is called:
Step-up transformer
Step-down transformer
Auto-transformer
Isolation transformer
Explanation - A step-up transformer increases voltage from primary to secondary coil.
Correct answer is: Step-up transformer
Q.23 Rate of change of magnetic flux is 0.1 Wb/s. Number of turns = 50. Induced EMF = ?
5 V
10 V
2 V
0.5 V
Explanation - EMF = N * (dΦ/dt) = 50 * 0.1 = 5 V.
Correct answer is: 5 V
Q.24 Which material is preferred for inductor cores to reduce energy loss?
Copper
Soft iron
Aluminum
Plastic
Explanation - Soft iron has high magnetic permeability and low hysteresis loss, ideal for inductor cores.
Correct answer is: Soft iron
Q.25 The property of a material to oppose the change in magnetic flux is called:
Resistance
Inductance
Capacitance
Conductance
Explanation - Inductance is the property by which a conductor opposes change in current via induced EMF.
Correct answer is: Inductance