Q: An induced EMF of 6\text{ V} acts in a circuit of resistance 3\,\Omega. The induced current is:

2\text{ A}. I = \dfrac{e}{R} = \dfrac{6}{3} = 2\text{ A}.

Question 1

Lenz's law states that the induced current flows in such a direction as to:

Accepted Answer

Oppose the change in flux that produces it. This is what the negative sign in e = -N\dfrac{d\Phi}{dt} represents.

Question 2

Lenz's law is a direct consequence of the conservation of:

Accepted Answer

Energy. If the induced current assisted the change, the motion would accelerate on its own and energy would be created from nothing.

Question 3

When the north pole of a bar magnet is pushed towards a closed coil, the face of the coil towards the magnet:

Accepted Answer

Behaves as a north pole and repels the magnet. By Lenz's law the coil opposes the approach, so it must present a like pole to the incoming magnet.

Question 4

When a bar magnet is withdrawn from a closed coil, the coil:

Accepted Answer

Attracts the magnet, opposing its withdrawal. Opposing the decrease in flux means trying to hold the magnet back.

Question 5

The direction of the current induced in a straight conductor moving in a magnetic field is given by:

Accepted Answer

Fleming's right-hand rule. Fleming's left-hand rule applies to the force on a current; the right-hand rule applies to induced current.

Question 6

The mechanical work done against the opposing force during electromagnetic induction is converted into:

Accepted Answer

Electrical energy in the circuit. This conversion is the working principle of every electrical generator.

Question 7

Lenz's law does not violate the principle of conservation of energy because:

Accepted Answer

Work must be done against the opposing force to maintain the change. The electrical energy that appears is exactly paid for by the mechanical work done by the agent producing the change.

Question 8

If the flux through a coil is increasing, the induced current in the coil flows so as to:

Accepted Answer

Set up a flux opposing the increase. Opposition to an increase means the induced flux points opposite to the original.

Question 9

A copper ring is dropped so that a bar magnet passes through it. During the fall the ring:

Accepted Answer

Experiences a retarding force from the induced current. By Lenz's law the induced current opposes the relative motion, so the ring resists the magnet's approach and departure.

Question 10

An induced EMF of 6	ext{ V} acts in a circuit of resistance 3\,\Omega. The induced current is:

Accepted Answer

2	ext{ A}. I = \dfrac{e}{R} = \dfrac{6}{3} = 2	ext{ A}.

Question 11

An induced EMF of 10	ext{ V} acts in a circuit of resistance 5\,\Omega. The power dissipated is:

Accepted Answer

20	ext{ W}. P = \dfrac{e^2}{R} = \dfrac{100}{5} = 20	ext{ W}.

Question 12

A single-turn coil of resistance 2\,\Omega has its flux changed by 0.2	ext{ Wb}. The charge that circulates is:

Accepted Answer

0.1	ext{ C}. q = \dfrac{\Delta\Phi}{R} = \dfrac{0.2}{2} = 0.1	ext{ C}.

Question 13

A coil produces an EMF of 10	ext{ V} when the flux through it changes at 0.05	ext{ Wb}/	ext{s}. The number of turns is:

Accepted Answer

200. N = \dfrac{e}{d\Phi/dt} = \dfrac{10}{0.05} = 200.

Question 14

A current of 2	ext{ A} is induced in a circuit of resistance 5\,\Omega for 10	ext{ s}. The heat generated is:

Accepted Answer

200	ext{ J}. H = I^2Rt = 4 	imes 5 	imes 10 = 200	ext{ J}.

Question 15

A coil of resistance 4\,\Omega has an induced EMF of 8	ext{ V}. The induced current is:

Accepted Answer

2	ext{ A}. I = \dfrac{8}{4} = 2	ext{ A}.

Question 16

The charge that flows through a coil during a flux change is:

Accepted Answer

Independent of the time taken for the change. q = \dfrac{N\Delta\Phi}{R} contains no time term: a slow change gives a small current for a long time, and vice versa.

Question 17

If the same flux change occurs in half the time, the induced EMF becomes:

Accepted Answer

Twice as large. e \propto \dfrac{1}{\Delta t} for a given \Delta\Phi.

Question 18

If the magnetic field through a coil is doubled over the same time interval, the induced EMF:

Accepted Answer

Doubles. The flux change doubles while the time is unchanged, so the EMF doubles.

Question 19

A coil of 100 turns and resistance 20\,\Omega has its flux changed by 0.04	ext{ Wb}. The charge that flows is:

Accepted Answer

0.2	ext{ C}. q = \dfrac{100 	imes 0.04}{20} = 0.2	ext{ C}.

Question 20

An induced EMF of 12	ext{ V} drives a current through a resistance of 6\,\Omega. The power dissipated is:

Accepted Answer

24	ext{ W}. P = \dfrac{e^2}{R} = \dfrac{144}{6} = 24	ext{ W}.

Lenz's Law & Induced EMF — MH-CET Physics MCQs with Solutions

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