Assertion A: A bar magnet dropped along the axis of a closed horizontal coil falls with an acceleration less than g while approaching the coil. Reason R: The current induced in the coil produces an effect that opposes the relative motion of the magnet and the coil. Choose the correct answer.

Both A and R are correct and R is the correct explanation of A

Both A and R are correct but R is not the correct explanation of A

A is not correct but R is correct

A is correct but R is not correct

Given below are two statements about the arrangement drawn, in which the magnet approaches the closed coil: Statement I: The induced current in the coil is anticlockwise when viewed from the magnet's side. Statement II: The face of the coil towards the magnet behaves as a south pole. Choose the correct answer.

Statement I is correct but Statement II is incorrect

Both Statement I and Statement II are incorrect

Both Statement I and Statement II are correct

Statement I is incorrect but Statement II is correct

Electromagnetic Induction

7 NEET-UG practice questions on Electromagnetic Induction, part of Physics. The first 7 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
The current in an inductor of 200 mH rises from 2 A to 4 A. By how much does the energy stored in its magnetic field increase?
1. A0.4 J
2. B2.4 J
3. C1.6 J
4. D1.2 J
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Answer: D · 1.2 J
Stored energy is U = (1/2)LI². The increase is (1/2)(0.2)(4² - 2²) = 0.1 × 12 = 1.2 J.
- A: The change in current was squared, (1/2)L(ΔI)².
- B: The factor 1/2 was left out.
- C: This is the final energy alone, without subtracting the initial energy.
Remember this
Energy depends on I², so subtract the two energies; do not use the change in current in the formula.
Question 2 · Easy
A coil of 50 turns has its flux per turn reduced steadily from 8 mWb to 2 mWb in 0.02 s. What emf is induced in the coil?
1. A15 V
2. B25 V
3. C0.3 V
4. D20 V
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Answer: A · 15 V
Faraday's law gives |e| = N ΔΦ/Δt = 50 × (6 × 10⁻³)/0.02 = 15 V.
- B: The two flux values were added instead of subtracted.
- C: The number of turns was left out.
- D: The initial flux was used in place of the change in flux.
Remember this
Induced emf depends on the change in flux per unit time, multiplied by the number of turns.
Question 3 · Medium
A rod of length 40 cm slides at a constant 5 m/s on smooth parallel rails closed by a 2 Ω resistor. A uniform field of 0.5 T is perpendicular to the plane of the rails. Rod and rails have negligible resistance. What external force keeps the rod moving at this speed?
1. A0.1 N
2. B0.5 N
3. C1.0 N
4. D0.2 N
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Answer: A · 0.1 N
The motional emf is Blv = 0.5 × 0.4 × 5 = 1 V, so I = 1/2 = 0.5 A. The opposing force is BIl = 0.5 × 0.5 × 0.4 = 0.1 N, which the external force must balance. Check: Fv = 0.5 W equals I²R = 0.5 W.
- B: This is the value of the current, or of the power, not the force.
- C: This is the emf in volts, not a force.
- D: The factor R was left out of B²l²v/R.
Remember this
The retarding force on a sliding rod is B²l²v/R; mechanical power Fv appears as heat I²R.
Question 4 · Medium
Assertion A: A bar magnet dropped along the axis of a closed horizontal coil falls with an acceleration less than g while approaching the coil. Reason R: The current induced in the coil produces an effect that opposes the relative motion of the magnet and the coil. Choose the correct answer.
1. ABoth A and R are correct and R is the correct explanation of A
2. BBoth A and R are correct but R is not the correct explanation of A
3. CA is not correct but R is correct
4. DA is correct but R is not correct
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Answer: A · Both A and R are correct and R is the correct explanation of A
By Lenz's law, the induced current makes the coil's near face a like pole of the approaching one, which repels the magnet. This upward force on the magnet reduces its acceleration below g, so R explains A.
- B: The opposing force is the very cause of the reduced acceleration.
- C: A is what is observed with a closed coil.
- D: R is Lenz's law, which is correct.
Remember this
Lenz's law follows from energy conservation; the opposing force does work that appears as induced electrical energy.
Question 5 · Easy
Given below are two statements about the arrangement drawn, in which the magnet approaches the closed coil: Statement I: The induced current in the coil is anticlockwise when viewed from the magnet's side. Statement II: The face of the coil towards the magnet behaves as a south pole. Choose the correct answer.
Figure: MedExams
1. ABoth Statement I and Statement II are incorrect
2. BBoth Statement I and Statement II are correct
3. CStatement I is incorrect but Statement II is correct
4. DStatement I is correct but Statement II is incorrect
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Answer: D · Statement I is correct but Statement II is incorrect
By Lenz's law the coil opposes the approach, so its near face must repel the approaching north pole: it becomes a north pole. A face with anticlockwise current, as seen from that side, is a north pole. So Statement I is correct and Statement II is not.
- A: Rejects a correct application of the Lenz's law to the coil.
- B: A south face would attract the magnet and add energy from nowhere.
- C: Reverses the current and the pole that the coil forms.
Remember this
Lenz's law: an approaching pole meets a like pole. Anticlockwise current seen from a face makes that face north.
Question 6 · Hard
Switch S is closed at t = 0 in this circuit; the cell is ideal and the inductor has no resistance of its own. Find the cell current just after closing S and the energy stored in the inductor a long time later.
Figure: MedExams
1. A3 A and 1 J
2. B1.5 A and 2.25 J
3. C6 A and 2.25 J
4. D1.5 A and 1 J
Answer and explanation in LearnFree account
Question 7 · Medium
A rod slides on smooth conducting rails with the speed marked, in a uniform field. Rails and rod have negligible resistance. Find the current in the circuit and its sense as seen in the figure.
Figure: MedExams
1. A2 A, anticlockwise
2. B1 A, anticlockwise
3. C0.5 A, clockwise
4. D0.5 A, anticlockwise
Answer and explanation in LearnFree account

Electromagnetic Induction

The current in an inductor of 200 mH rises from 2 A to 4 A. By how much does the energy stored in its magnetic field increase?

A coil of 50 turns has its flux per turn reduced steadily from 8 mWb to 2 mWb in 0.02 s. What emf is induced in the coil?

A rod of length 40 cm slides at a constant 5 m/s on smooth parallel rails closed by a 2 Ω resistor. A uniform field of 0.5 T is perpendicular to the plane of the rails. Rod and rails have negligible resistance. What external force keeps the rod moving at this speed?

Assertion A: A bar magnet dropped along the axis of a closed horizontal coil falls with an acceleration less than g while approaching the coil. Reason R: The current induced in the coil produces an effect that opposes the relative motion of the magnet and the coil. Choose the correct answer.

Switch S is closed at t = 0 in this circuit; the cell is ideal and the inductor has no resistance of its own. Find the cell current just after closing S and the energy stored in the inductor a long time later.

A rod slides on smooth conducting rails with the speed marked, in a uniform field. Rails and rod have negligible resistance. Find the current in the circuit and its sense as seen in the figure.