Electromagnetic Induction and Alternating Currents — NEET Physics MCQs with answers

Electromagnetic Induction and Alternating Currents is a Class 12 Physics chapter in the NEET (UG) syllabus. NEET720 has 676 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Faraday's and Lenz's laws · AC measurement · AC in conductors · Motional EMF · Self and mutual inductance · AC fundamentals · Phasors and LCR circuits · Resonance and power in AC · Transformers and AC generator · Electromagnetic induction · Magnetic flux · Faraday's law · Motional EMF · Self-inductance · Mutual inductance · Energy in inductor · Lenz's law · AC fundamentals · Inductive reactance · Capacitive reactance · Series LCR circuit · Resonance in LCR circuit · AC generator · Eddy currents · LC oscillations · Magnetic flux · Energy stored in inductor · AC circuits with single element · Series LR circuit · Series CR circuit · Series LCR circuit · Resonance in LCR circuit · Quality factor · Choke coil · Faraday's laws · LR Circuits · Alternating Current · Magnetic Energy · Faraday's Law · Self Inductance

8 free Electromagnetic Induction and Alternating Currents practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · medium · Faraday's and Lenz's laws

   A conducting square loop lies partly inside a uniform magnetic field directed into the page. The loop is pulled steadily to the right so that it is exiting the field region (its right edge already outside, left edge still inside). The direction of the induced current in the loop is:

   • A.Counterclockwise, opposing the decrease of the into-the-page flux
   • B.Clockwise, opposing the decrease of the into-the-page flux
   • C.Clockwise, aiding the decrease of the into-the-page flux
   • D.No current is induced because the loop moves at constant velocity
   Show answer and explanation

   Answer: B. Clockwise, opposing the decrease of the into-the-page flux

   As the loop exits, the into-the-page flux through it decreases. By Lenz's law the induced current must create its own into-the-page field inside the loop to oppose this decrease, which by the right-hand rule means clockwise current.

   While the loop is partly inside the field and moving out, the area of the loop still inside the field shrinks with time, so the into-the-page flux linked with the loop decreases steadily even though the loop's velocity is constant. Lenz's law requires the induced current to oppose this decrease, i.e., to try to maintain the into-the-page flux. By the right-hand rule, a current that produces a field into the page (inside the loop) must flow clockwise when viewed from the reader's side. The current does not aid the change (that would violate energy conservation), and it is certainly nonzero as long as the flux is changing, regardless of the loop's velocity being constant.

   Common mistake: Assuming constant velocity implies constant flux, or reversing the right-hand rule sense.

2. Question 2 · easy · Faraday's and Lenz's laws

   Lenz's law, which fixes the direction of an induced current, is essentially a statement of which fundamental principle?

   • A.Conservation of energy
   • B.Conservation of linear momentum
   • C.Conservation of electric charge
   • D.Conservation of magnetic flux
   Show answer and explanation

   Answer: A. Conservation of energy

   If the induced current aided the change producing it, the effect would keep amplifying its own cause, creating energy from nothing. Lenz's law (opposition to the change) keeps energy conserved.

   Suppose the induced current supported (rather than opposed) the change in flux — e.g., a magnet approaching a coil experienced an attractive pull from the induced current. The magnet would then accelerate on its own, gaining kinetic energy plus supplying electrical energy to the circuit, with no external energy input — violating energy conservation. Lenz's law prevents this: the induced effects always oppose the change, so external work must be done to sustain the change, and that external work is the source of the electrical energy delivered. Hence Lenz's law is the electromagnetic-induction expression of energy conservation.

   Common mistake: Attributing Lenz's law to momentum or flux conservation instead of energy conservation.

3. Question 3 · easy · Faraday's and Lenz's laws

   A bar magnet is held with its north pole facing a stationary coil and is pushed horizontally toward the coil along its axis. As seen by an observer facing the approaching north pole, the induced current in the coil flows:

   • A.Clockwise, so that face of the coil acts as a south pole and repels the approaching magnet
   • B.Anticlockwise, so that face of the coil acts as a north pole and repels the approaching magnet
   • C.Clockwise, so that face of the coil acts as a north pole and attracts the approaching magnet
   • D.No current is induced unless the magnet actually touches the coil
   Show answer and explanation

   Answer: B. Anticlockwise, so that face of the coil acts as a north pole and repels the approaching magnet

   The approaching north pole increases flux into the coil's near face; by Lenz's law the coil opposes this by presenting a north pole toward the magnet, which requires an anticlockwise current (as viewed facing that pole).

   As the magnet's N pole approaches, flux through the coil (directed away from the N pole, i.e., toward the coil) increases. Lenz's law demands the induced current opposes this increase, so the coil's near face must become a north pole to repel the magnet and resist its approach. By the right-hand rule, a face acts as a north pole when current flows anticlockwise as viewed from that face. Hence the current is anticlockwise as seen facing the approaching pole.

   Common mistake: Assuming the coil attracts the magnet, or inverting the clockwise/anticlockwise-to-pole correspondence.

4. Question 4 · medium · Faraday's and Lenz's laws

   A student states: "Eddy currents are always undesirable and engineers only ever try to eliminate them." This statement is:

   • A.True — eddy currents only ever cause energy loss and are never put to practical use
   • B.True, except in transformers, where eddy currents are actually beneficial
   • C.False, because eddy currents do not actually exist; they are only a theoretical idealization
   • D.False — eddy currents are deliberately exploited in devices such as induction furnaces, induction cooktops, and electromagnetic braking systems
   Show answer and explanation

   Answer: D. False — eddy currents are deliberately exploited in devices such as induction furnaces, induction cooktops, and electromagnetic braking systems

   While eddy currents cause unwanted heating losses in transformer/motor cores (reduced by lamination), they are intentionally used for induction heating, electromagnetic braking, and speedometers — so the blanket claim is false.

   Eddy currents are induced whenever a bulk conductor experiences changing flux, and they dissipate energy as heat. In transformer and motor cores this is a loss to be minimized (hence laminated cores). However, this same heating and damping effect is deliberately harnessed elsewhere: induction furnaces/cooktops use eddy-current heating to melt or cook metal without contact, and electromagnetic brakes in trains and roller coasters use eddy-current drag to smoothly dissipate kinetic energy without mechanical wear. So eddy currents are context-dependent — sometimes a loss to minimize, sometimes a useful effect to exploit — and the blanket claim in the question is false.

   Common mistake: Assuming eddy currents are inherently and universally a nuisance to be eliminated.

5. Question 5 · medium · Faraday's and Lenz's laws

   Two coaxial circular coils P and Q face each other, a short distance apart. The current in coil P is steadily increased. The force experienced by coil Q, and its cause, is:

   • A.A repulsive force, because the current induced in Q (by Lenz's law) opposes the increasing flux from P, making Q's near face effectively like P's near face
   • B.An attractive force, because induced currents always create fields that pull the source of the change closer
   • C.No force at all, since coil Q is not connected to a battery
   • D.A repulsive force only while P's current is constant, and attractive while it changes
   Show answer and explanation

   Answer: A. A repulsive force, because the current induced in Q (by Lenz's law) opposes the increasing flux from P, making Q's near face effectively like P's near face

   By Lenz's law, Q's induced current opposes the increasing flux from P, so Q's near face develops the same polarity as P's near face — like poles facing like poles repel.

   As P's current increases, the flux it sends through Q increases. Lenz's law says the induced current in Q must oppose this increase, which means Q's induced current creates a magnetic field, on the face toward P, that points opposite to P's field there — i.e., Q's near face becomes magnetically 'like' P's near face (same sense of circulation as needed to oppose, which works out to like-pole orientation). Like poles repel, so P and Q push apart. This is a standard qualitative NEET check on combining Lenz's law with force-between-currents reasoning; note the force exists only while P's current is changing — once P's current becomes steady, Q's induced current (and hence the extra force) disappears.

   Common mistake: Assuming induced effects always attract, rather than checking whether they act to oppose the flux increase.

6. Question 6 · medium · Faraday's and Lenz's laws

   A copper ring is placed just below the north pole of a bar magnet, coaxial with it, and the magnet is suddenly dropped so it falls toward and then through the ring. Compared to an identical non-conducting (say, wooden) ring of the same size, the time taken by the magnet to fall through the conducting ring's plane is:

   • A.The same, because the ring's material does not affect the magnet's free-fall motion under gravity
   • B.Shorter, because the induced current in the ring pulls the magnet through faster
   • C.Longer, because the induced eddy current in the conducting ring opposes the magnet's approach and later its departure, retarding its motion
   • D.Longer only while approaching the ring, but shorter while leaving it, so the two effects cancel and total time is unchanged
   Show answer and explanation

   Answer: C. Longer, because the induced eddy current in the conducting ring opposes the magnet's approach and later its departure, retarding its motion

   By Lenz's law, the conducting ring's induced current always opposes the relative motion of the magnet — repelling it on approach and attracting it back on departure — so it takes longer to fall through than through a non-conducting ring, where no such force exists.

   As the magnet approaches the conducting ring, flux through the ring increases, inducing a current that (by Lenz's law) opposes the approach — this manifests as a repulsive force slowing the magnet down. As the magnet passes through and moves away, flux decreases, inducing a current that opposes the departure — manifesting as an attractive force, again slowing the magnet. Both phases retard the magnet's motion (they do not cancel; they both act against relative motion), so the magnet takes measurably longer to fall through a conducting ring than through an otherwise identical non-conducting ring, where no eddy currents (and hence no retarding force) exist. This is a classic, frequently-cited NEET demonstration/thought experiment for Lenz's law.

   Common mistake: Assuming the retarding effects during approach and departure act in opposite senses and cancel out.

7. Question 7 · easy · Transformers and AC generator

   An AC generator uses two continuous slip rings (rather than a split-ring commutator like a DC generator) to connect its rotating coil to the external circuit. What role do the slip rings play in producing an AC output?

   • A.The slip rings periodically reverse the connection to the external circuit every half cycle, converting the alternating EMF into a unidirectional current.
   • B.The slip rings are used only to increase the frequency of rotation, which is what makes the output AC.
   • C.The slip rings merely reduce friction between the brushes and the rotating shaft and have no effect on the nature of the output waveform.
   • D.The slip rings maintain a continuous, unbroken connection between each end of the rotating coil and its respective fixed external terminal, so the EMF that is naturally alternating (due to the coil's rotation) is delivered to the external circuit unchanged, as AC.
   Show answer and explanation

   Answer: D. The slip rings maintain a continuous, unbroken connection between each end of the rotating coil and its respective fixed external terminal, so the EMF that is naturally alternating (due to the coil's rotation) is delivered to the external circuit unchanged, as AC.

   A rotating coil in a uniform field always generates a sinusoidally alternating EMF; slip rings simply pass this EMF through to the external circuit without altering it, unlike a split-ring commutator which reverses the connection every half cycle to produce a rectified (DC-like) output.

   As a coil rotates in a uniform magnetic field, the flux through it varies sinusoidally, so by Faraday's law the induced EMF is inherently alternating — this is true regardless of how it is picked off. The two slip rings are fixed to the two ends of the coil and rotate with it, each always touching the same stationary brush; this continuous, non-switching contact means the alternating EMF generated in the coil is passed straight through to the external circuit as AC. A split-ring commutator, by contrast, is built so that the connection to the external circuit reverses every half cycle in step with the EMF reversal, which rectifies the output into a unidirectional (though pulsating) current — this is how a DC generator is built from essentially the same rotating-coil principle.

   Common mistake: Confusing the function of slip rings with that of a split-ring commutator.

8. Question 8 · hard · Motional EMF

   A rod of length 1 m rotates with angular speed 10 rad/s about one end, in a plane perpendicular to a magnetic field of 0.4 T. The EMF induced between its ends is:

   • A.2 V
   • B.4 V
   • C.1 V
   • D.0.4 V
   Show answer and explanation

   Answer: A. 2 V

   EMF=½BωL²=½(0.4)(10)(1)²=2 V.

   For a rod rotating about one end in a uniform field perpendicular to the plane of rotation, EMF=½BωL². Substituting B=0.4 T, ω=10 rad/s, L=1 m: EMF=0.5×0.4×10×1=2 V.

   Common mistake: Forgetting the factor of ½ that arises from integrating over the rod's length

Questions about Electromagnetic Induction and Alternating Currents for NEET

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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (676 active practice questions in this chapter today).