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

22 NEET-UG practice questions on Electromagnetic Induction, part of Physics. The first 22 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
Question 8 · Medium
Two coils have a mutual inductance of 0.05 H. The current in the first coil rises steadily from 0 to 4 A in 0.02 s. What emf is induced in the second coil?
1. A0.004 V
2. B5 V
3. C10 V
4. D0.2 V
Answer and explanation in LearnFree account
Question 9 · Medium
A metal rod 1 m long rotates at 20 rad/s about an axis through one end, perpendicular to the rod and parallel to a uniform magnetic field of 0.5 T. What emf is induced between its ends?
1. A5 V
2. B2.5 V
3. C20 V
4. D10 V
Answer and explanation in LearnFree account
Question 10 · Hard
A flat coil of 100 turns and area 0.01 m² has a total resistance of 5 Ω. It lies with its plane perpendicular to a uniform magnetic field of 0.5 T and is quickly turned through 180° about a diameter. How much charge flows through the coil?
1. A0.2 C
2. B0.002 C
3. CZero
4. D0.1 C
Answer and explanation in LearnFree account
Question 11 · Easy
Lenz's law says the induced current opposes the change that produces it. This law is a consequence of the conservation of which quantity?
1. AEnergy
2. BCharge
3. CMass
4. DLinear momentum
Answer and explanation in LearnFree account
Question 12 · Hard
Two long vertical frictionless conducting rails, 40 cm apart, are joined at the top by a 2 Ω resistor. A horizontal metal rod of mass 20 g slides down them while staying in contact, in a uniform horizontal magnetic field of 0.5 T perpendicular to the plane of the rails. Neglecting the resistance of the rod and rails and taking g = 10 m/s², what terminal speed does the rod reach?
1. A2 m/s
2. B4 m/s
3. C5 m/s
4. D10 m/s
Answer and explanation in LearnFree account
Question 13 · Medium
A long solenoid of self-inductance L carries current I. Another solenoid of the same length and cross-section is wound with twice the number of turns and carries current I/2. Compared with the first, how much magnetic energy does the second store?
1. AThe same amount
2. BFour times as much
3. CTwice as much
4. DHalf as much
Answer and explanation in LearnFree account
Question 14 · Easy
Transformer cores are built from thin insulated sheets of soft iron rather than one solid block. What is the main purpose of this lamination?
1. ATo increase the mutual inductance of the coils
2. BTo reduce the hysteresis of the iron
3. CTo reduce energy loss by eddy currents
4. DTo make the core lighter and cheaper
Answer and explanation in LearnFree account
Question 15 · Medium
In a coil of self-inductance 0.2 H, the current falls steadily from 3 A to 1 A in 0.1 s. What is the magnitude of the self-induced emf?
1. A4 V
2. B0.04 V
3. C6 V
4. D8 V
Answer and explanation in LearnFree account
Question 16 · Hard
A coil of inductance 2 H and resistance 5 Ω is connected at t = 0 to a 10 V battery of negligible internal resistance. At the instant the current reaches 1 A, at what rate is the current increasing, and what is the final steady current?
1. A2.5 A/s and 2 A
2. B5 A/s and 2 A
3. C2.5 A/s and 0.5 A
4. D7.5 A/s and 2 A
Answer and explanation in LearnFree account
Question 17 · Medium
A long solenoid has self-inductance L. Its number of turns is doubled and its length is also doubled, the cross-sectional area staying the same. What is its new self-inductance?
1. A4L
2. B2L
3. CL/2
4. DL
Answer and explanation in LearnFree account
Question 18 · Medium
A bar magnet held vertically above a conducting ring lying flat on a table is moved quickly down towards it, north pole first. Seen from above, what is the direction of the induced current in the ring, and how does the ring act on the magnet?
1. AClockwise; the ring repels the magnet
2. BAnticlockwise; the ring attracts the magnet
3. CAnticlockwise; the ring repels the magnet
4. DClockwise; the ring attracts the magnet
Answer and explanation in LearnFree account
Question 19 · Easy
Which of these is equivalent to one henry?
1. A1 V s A⁻¹
2. B1 T m² s⁻¹
3. C1 V A s⁻¹
4. D1 Wb A
Answer and explanation in LearnFree account
Question 20 · Medium
A generator coil of 100 turns, each of area 0.05 m², rotates at 100 rad/s about an axis perpendicular to a uniform magnetic field of 0.1 T. What is the peak emf?
1. A8 V
2. B50 V
3. C0.5 V
4. D35 V
Answer and explanation in LearnFree account
Question 21 · Easy
A coil of 100 turns, each of area 0.02 m², is placed with its plane perpendicular to a uniform magnetic field of 0.5 T. What is the total magnetic flux linked with the coil?
1. A50 Wb
2. B1 Wb
3. CZero
4. D0.01 Wb
Answer and explanation in LearnFree account
Question 22 · Medium
Given below are two statements: Statement I: No motional emf is induced in a straight conducting rod that moves along its own length through a uniform magnetic field. Statement II: The self-inductance of an air-cored coil depends on the current flowing through it. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BBoth Statement I and Statement II are incorrect
3. CStatement I is incorrect but Statement II is correct
4. DStatement I is correct but Statement II is incorrect
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.

Two coils have a mutual inductance of 0.05 H. The current in the first coil rises steadily from 0 to 4 A in 0.02 s. What emf is induced in the second coil?

A metal rod 1 m long rotates at 20 rad/s about an axis through one end, perpendicular to the rod and parallel to a uniform magnetic field of 0.5 T. What emf is induced between its ends?

A flat coil of 100 turns and area 0.01 m² has a total resistance of 5 Ω. It lies with its plane perpendicular to a uniform magnetic field of 0.5 T and is quickly turned through 180° about a diameter. How much charge flows through the coil?

Lenz's law says the induced current opposes the change that produces it. This law is a consequence of the conservation of which quantity?

A long solenoid of self-inductance L carries current I. Another solenoid of the same length and cross-section is wound with twice the number of turns and carries current I/2. Compared with the first, how much magnetic energy does the second store?

Transformer cores are built from thin insulated sheets of soft iron rather than one solid block. What is the main purpose of this lamination?

In a coil of self-inductance 0.2 H, the current falls steadily from 3 A to 1 A in 0.1 s. What is the magnitude of the self-induced emf?

A coil of inductance 2 H and resistance 5 Ω is connected at t = 0 to a 10 V battery of negligible internal resistance. At the instant the current reaches 1 A, at what rate is the current increasing, and what is the final steady current?

A long solenoid has self-inductance L. Its number of turns is doubled and its length is also doubled, the cross-sectional area staying the same. What is its new self-inductance?

A bar magnet held vertically above a conducting ring lying flat on a table is moved quickly down towards it, north pole first. Seen from above, what is the direction of the induced current in the ring, and how does the ring act on the magnet?

Which of these is equivalent to one henry?

A generator coil of 100 turns, each of area 0.05 m², rotates at 100 rad/s about an axis perpendicular to a uniform magnetic field of 0.1 T. What is the peak emf?

A coil of 100 turns, each of area 0.02 m², is placed with its plane perpendicular to a uniform magnetic field of 0.5 T. What is the total magnetic flux linked with the coil?

Given below are two statements: Statement I: No motional emf is induced in a straight conducting rod that moves along its own length through a uniform magnetic field. Statement II: The self-inductance of an air-cored coil depends on the current flowing through it. Choose the correct answer.