Chapter 6: Electromagnetic Induction Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): The galvanometer shows a deflection when a bar magnet is moved toward a coil, but shows no deflection when the magnet is held stationary inside the coil. Reason (R): An emf is induced in a coil only when the magnetic flux through it changes with time.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 2

Logic Check

Assertion (A): Lenz's law violates the law of conservation of energy. Reason (R): The induced current always opposes the change in magnetic flux that produced it, requiring work to be done against the opposing force.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): The induced emf in a coil increases when the number of turns N is increased, even if the rate of flux change remains the same. Reason (R): The induced emf is given by ε = −N(dΦB/dt), which is directly proportional to N.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): The motional emf ε = Blv and the Faraday's law expression for a moving conductor give the same result. Reason (R): The motional emf arises from the Lorentz force on charge carriers, which is equivalent to Faraday's law for conductors moving in time-independent magnetic fields.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The number of spokes in a rotating wheel generator affects the total induced emf between the axle and the rim. Reason (R): Each spoke generates the same emf and all spokes are connected in parallel between the axle and the rim.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): Self-inductance is the electromagnetic analogue of mass in mechanics. Reason (R): Just as mass opposes a change in velocity, self-inductance opposes any change in the current through a coil, and the energy stored (1/2)LI² is analogous to kinetic energy (1/2)mv².

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 7

Logic Check

Assertion (A): The induced emf in a rectangular loop exiting a uniform magnetic field at constant velocity is constant, but not so for a circular loop exiting at the same velocity. Reason (R): For the rectangular loop, the length of wire at the boundary of the field is constant, but for the circular loop it varies continuously.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): Inserting a soft iron rod inside two stationary coils in Faraday's Experiment 6.3 dramatically increases the galvanometer deflection. Reason (R): Soft iron has high relative permeability, which increases the magnetic flux linkage between the coils and hence the mutual inductance.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 9

Logic Check

Assertion (A): No current is induced in a closed loop moving with constant velocity completely inside a uniform magnetic field. Reason (R): The magnetic flux through the loop remains constant when the loop is entirely within the uniform field, giving dΦB/dt = 0.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 10

Logic Check

Assertion (A): M12 = M21 for any pair of coils. Reason (R): This equality is true only for long coaxial solenoids and does not hold for other geometric configurations.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): In an AC generator, the emf is zero when the plane of the coil is perpendicular to the magnetic field. Reason (R): At this position, the magnetic flux through the coil is maximum, and its rate of change is zero.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): Doubling the rotational speed of an AC generator doubles the peak emf and also doubles the frequency of the AC output. Reason (R): Peak emf ε0 = NBAω is proportional to ω, and the AC frequency equals the rotational frequency v = ω/(2π).

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 13

Logic Check

Assertion (A): A time-varying magnetic field generates an electric field even in the absence of any conductor. Reason (R): For a stationary conductor in a changing magnetic field, the Lorentz force q(v × B) drives the charges, since v = 0 makes the electric term zero.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): The energy stored in an inductor carrying current I is (1/2)LI². Reason (R): This energy is stored as magnetic potential energy in the magnetic field of the inductor and is analogous to the electrostatic energy (1/2)CV² stored in a capacitor.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 15

Logic Check

Assertion (A): The magnetic flux through a coil is maximum when the plane of the coil is perpendicular to the magnetic field. Reason (R): Magnetic flux is given by ΦB = BA cosθ, which is maximum when θ = 0°, i.e., when the area vector is parallel to B (the plane is perpendicular to B).

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 16

Logic Check

Assertion (A): In Faraday's Experiment 6.2, the current induced in coil C1 is due to the relative motion between the two coils. Reason (R): Electromagnetic induction can only occur when there is relative motion between a magnet (or current-carrying coil) and the other coil.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): The self-inductance of a solenoid depends on the current flowing through it. Reason (R): Self-inductance L = NΦB/I depends on the geometry of the coil and the permeability of the medium, not on the current.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): The polarity of plate A will be positive with respect to plate B in the capacitor situation described in Example 6.5(d) of the chapter. Reason (R): The direction of the induced emf (and hence the polarity) is determined by Lenz's law applied to the direction of motion of the loop relative to the magnetic field.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 19

Logic Check

Assertion (A): The induced emf is the same whether the coil moves toward a stationary magnet or the magnet moves toward a stationary coil with the same relative velocity. Reason (R): It is the relative motion between the magnet and the coil (not the absolute motion of either) that determines the rate of change of flux and hence the induced emf.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): The self-induced emf is called 'back emf' because it always acts in the direction opposite to the applied emf. Reason (R): The self-induced emf ε = −L(dI/dt) opposes any change in current — opposing increase when current rises and opposing decrease when current falls.

Reasoning Options

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Chapter sections

Chapter 6: Electromagnetic Induction | Assertion-Reason

Assertion (A): The galvanometer shows a deflection when a bar magnet is moved toward a coil, but shows no deflection when the magnet is held stationary inside the coil. Reason (R): An emf is induced in a coil only when the magnetic flux through it changes with time.

Assertion (A): Lenz's law violates the law of conservation of energy. Reason (R): The induced current always opposes the change in magnetic flux that produced it, requiring work to be done against the opposing force.

Assertion (A): The induced emf in a coil increases when the number of turns N is increased, even if the rate of flux change remains the same. Reason (R): The induced emf is given by ε = −N(dΦB/dt), which is directly proportional to N.

Assertion (A): The motional emf ε = Blv and the Faraday's law expression for a moving conductor give the same result. Reason (R): The motional emf arises from the Lorentz force on charge carriers, which is equivalent to Faraday's law for conductors moving in time-independent magnetic fields.

Assertion (A): The number of spokes in a rotating wheel generator affects the total induced emf between the axle and the rim. Reason (R): Each spoke generates the same emf and all spokes are connected in parallel between the axle and the rim.

Assertion (A): Self-inductance is the electromagnetic analogue of mass in mechanics. Reason (R): Just as mass opposes a change in velocity, self-inductance opposes any change in the current through a coil, and the energy stored (1/2)LI² is analogous to kinetic energy (1/2)mv².

Assertion (A): Inserting a soft iron rod inside two stationary coils in Faraday's Experiment 6.3 dramatically increases the galvanometer deflection. Reason (R): Soft iron has high relative permeability, which increases the magnetic flux linkage between the coils and hence the mutual inductance.

Assertion (A): No current is induced in a closed loop moving with constant velocity completely inside a uniform magnetic field. Reason (R): The magnetic flux through the loop remains constant when the loop is entirely within the uniform field, giving dΦB/dt = 0.

Assertion (A): M12 = M21 for any pair of coils. Reason (R): This equality is true only for long coaxial solenoids and does not hold for other geometric configurations.

Assertion (A): In an AC generator, the emf is zero when the plane of the coil is perpendicular to the magnetic field. Reason (R): At this position, the magnetic flux through the coil is maximum, and its rate of change is zero.

Assertion (A): Doubling the rotational speed of an AC generator doubles the peak emf and also doubles the frequency of the AC output. Reason (R): Peak emf ε0 = NBAω is proportional to ω, and the AC frequency equals the rotational frequency v = ω/(2π).

Assertion (A): A time-varying magnetic field generates an electric field even in the absence of any conductor. Reason (R): For a stationary conductor in a changing magnetic field, the Lorentz force q(v × B) drives the charges, since v = 0 makes the electric term zero.

Assertion (A): The energy stored in an inductor carrying current I is (1/2)LI². Reason (R): This energy is stored as magnetic potential energy in the magnetic field of the inductor and is analogous to the electrostatic energy (1/2)CV² stored in a capacitor.

Assertion (A): The magnetic flux through a coil is maximum when the plane of the coil is perpendicular to the magnetic field. Reason (R): Magnetic flux is given by ΦB = BA cosθ, which is maximum when θ = 0°, i.e., when the area vector is parallel to B (the plane is perpendicular to B).

Assertion (A): In Faraday's Experiment 6.2, the current induced in coil C1 is due to the relative motion between the two coils. Reason (R): Electromagnetic induction can only occur when there is relative motion between a magnet (or current-carrying coil) and the other coil.

Assertion (A): The self-inductance of a solenoid depends on the current flowing through it. Reason (R): Self-inductance L = NΦB/I depends on the geometry of the coil and the permeability of the medium, not on the current.

Assertion (A): The self-induced emf is called 'back emf' because it always acts in the direction opposite to the applied emf. Reason (R): The self-induced emf ε = −L(dI/dt) opposes any change in current — opposing increase when current rises and opposing decrease when current falls.

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