A Level Physics (A2) chapter 9: Magnetic fields MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

122 exam-style questions on Magnetic fields, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

122 questions · 5 topics · 10 per test

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What chapter 9 covers

Ten Magnetic fields questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. A proton moves at 3.0 × 106 m s−1 at right angles to a uniform magnetic field of flux density 0.25 T. What is the magnetic force on it?

  1. A
    1.2 × 10−13 N
  2. B
    1.3 × 10−21 N
  3. C
    3.6 × 10−7 N
  4. D
    1.3 × 10−26 N
Show answer

Answer: A. F = BQv = 0.25 × 1.60 × 10−19 × 3.0 × 106 = 1.2 × 10−13 N. The charge, not the mass, appears in the formula.

2. A magnet stands on a top-pan balance with a fixed horizontal wire between its poles, at right angles to the field. The length of wire in the field is 5.0 cm. When the current in the wire is 3.0 A, the balance reading changes by 2.4 g. What is the flux density between the poles?

  1. A
    0.016 T
  2. B
    0.16 T
  3. C
    1.6 × 10−3 T
  4. D
    160 T
Show answer

Answer: B. The force on the wire (equal to the change in force on the magnet) is 2.4 × 10−3 × 9.81 = 0.024 N. B = F/(IL) = 0.024 ÷ (3.0 × 0.050) = 0.16 T. Forgetting to multiply by g gives 0.016 T.

3. A soft-iron core is placed inside a solenoid carrying a constant current. Why does the magnetic flux density inside increase?

  1. A
    the iron lowers the resistance of the coil, so the current increases
  2. B
    the iron is magnetised by the field of the current, and its own field adds to it
  3. C
    part of the current flows along the iron core
  4. D
    the iron increases the speed of the electrons in the turns
Show answer

Answer: B. The iron is not part of the circuit. The field of the current magnetises it, and the iron's own field adds to the field of the solenoid, greatly increasing B.

4. A light aluminium ring rests on top of a coil wound on a vertical iron core. When a d.c. supply to the coil is switched on, the ring jumps up and then falls back, even though the current in the coil stays on. Why does the ring fall back?

  1. A
    the ring is attracted towards the core by the steady field of the coil
  2. B
    the induced current in the ring reverses direction and pulls the ring back down once the coil current becomes steady
  3. C
    aluminium cannot be magnetised, so the steady field has no effect on it
  4. D
    once the current in the coil is steady, the flux through the ring stops changing and no current is induced in it
Show answer

Answer: D. While the coil current is rising, the increasing flux induces a current in the ring that opposes the change, so the ring is repelled. When the current is steady, the flux is constant, no e.m.f. is induced and gravity pulls the ring back.

5. A circular loop of wire of radius 5.0 cm is perpendicular to a uniform magnetic field of flux density 0.040 T. What is the magnetic flux through the loop?

  1. A
    1.3 × 10−3 Wb
  2. B
    0.013 Wb
  3. C
    3.1 × 10−4 Wb
  4. D
    3.1 Wb
Show answer

Answer: C. Φ = BA = 0.040 × π × 0.0502 = 3.1 × 10−4 Wb. Using the diameter instead of the radius, or leaving the radius in centimetres, are the common slips.

6. Why can two magnetic field lines never cross?

  1. A
    the field at any point has only one direction
  2. B
    field lines repel each other
  3. C
    magnetic fields from different sources cannot overlap
  4. D
    the two fields would cancel at the crossing point
Show answer

Answer: A. A field line shows the direction of the resultant field. If two lines crossed, the field would have two directions at the same point, which is impossible. Fields from different sources do overlap: they add as vectors.

7. Which statement is Faraday's law of electromagnetic induction?

  1. A
    the induced e.m.f. is proportional to the rate of change of magnetic flux linkage
  2. B
    the induced e.m.f. is proportional to the magnetic flux linkage
  3. C
    the induced e.m.f. is proportional to the magnetic flux density
  4. D
    the induced current always flows so as to oppose the magnetic flux linkage
Show answer

Answer: A. Only a changing flux linkage induces an e.m.f., however large the flux itself. The direction of the e.m.f. (opposing the change) is given by Lenz's law.

8. A flat coil of 80 turns, each of area 25 cm2, starts with its plane perpendicular to a uniform magnetic field of flux density 0.20 T. It is turned through 180° in 0.050 s. What is the average e.m.f. induced?

  1. A
    0.80 V
  2. B
    0 V
  3. C
    0.020 V
  4. D
    1.6 V
Show answer

Answer: D. The flux linkage changes from +NBA to −NBA, a change of 2NBA = 2 × 80 × 0.20 × 25 × 10−4 = 0.080 Wb. Average e.m.f. = 0.080 ÷ 0.050 = 1.6 V. Missing the reversal of the flux halves the answer.

9. A taut horizontal wire passes at right angles through a steady, uniform horizontal magnetic field. The wire carries an alternating current of frequency 50 Hz. What is observed?

  1. A
    the wire is pushed steadily to one side
  2. B
    the wire stays still, because the average current is zero
  3. C
    the wire is pushed along its own length, first one way then the other
  4. D
    the wire vibrates at 50 Hz
Show answer

Answer: D. The force BIL reverses each time the current reverses, so it acts first one way then the other at right angles to the wire and to the field, making the wire vibrate at the supply frequency of 50 Hz.

10. Which statement about a magnetic field pattern drawn with field lines is correct?

  1. A
    the flux density is greater where the lines are further apart
  2. B
    the flux density is greater where the lines are closer together
  3. C
    the lines are closest where the force on a stationary charge is greatest
  4. D
    two lines may cross where the fields of two magnets overlap
Show answer

Answer: B. The spacing of the lines shows the strength of the field: closer lines mean a larger flux density. Lines never cross, because the field at a point has only one direction.

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Ways to practise this chapter

Magnetic fields: questions students ask

How many Magnetic fields MCQs are there?

122, each with the answer and a short explanation, across 5 topics: Concept of a magnetic field, Force on a current-carrying conductor, Force on a moving charge, Magnetic fields due to currents, Electromagnetic induction. Every chapter test draws ten of them, so you can take it many times.

Is the A Level Physics (A2) chapter 9 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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