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Magnetic fields: WJEC A‑Level Physics questions

Every WJEC A-Level Physics exam question on 4.4 Magnetic fields, 2016–2025, with its mark scheme and examiner’s report.

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Calculations

1,173 questions

  1. Q4(a)(i)

    Summer 2025 · Unit 4

    3 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(a)(i): Explain why a valid equation for the motion of the proton while inside a dee is: mω2r = Bqω r where m is the mass of the proton, ω is the angular velocity of th

  2. Q4(a)(ii)

    Summer 2025 · Unit 4

    3 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(a)(ii): Hence or otherwise, calculate the magnetic flux density. [3]

  3. Q4(b)

    Summer 2025 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(b): Each time the proton crosses between the dees, it is accelerated by a pd of 1.2 kV. Calculate the increase in kinetic energy in J of the proton each time it cro

  4. Q4(c)(i)

    Summer 2025 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(c)(i): Show that this happens when the proton has a kinetic energy of approximately 1 pJ. [2]

  5. Q4(c)(ii)

    Summer 2025 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(c)(ii): The proton is accelerated twice per cycle. Determine whether the proton spends more than a millisecond in the cyclotron if it is accelerated from rest. [2]

  6. Q4(d)

    Summer 2025 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2025 Unit 4, question 4(d): ‘All money spent on particle accelerators is wasted!’ Discuss this statement briefly. [2]

  7. Q5(a)

    Summer 2024 · Unit 4

    1 mark4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(a): is plotted using the corrected B -field. Measured Corrected a / m ln (a / m) ln (B / T) B -field / T B -field, B / T 0.010 0.000 529 0.000 499 −4.61 −7.60 0.020

  8. Q5(b)

    Summer 2024 · Unit 4

    3 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(b): Complete the table above and plot the missing point on the graph opposite (no error bars are required). [3]

  9. Q5(c)

    Summer 2024 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(c): The gradient of the steepest line is −1.03. Calculate the gradient of the least steep line. [2] ln (a / m) _ 5.00 _ 4.50 _ 4.00 _ 3.50 _ 3.00 _ 2.50 _ 2.00 _ 1.

  10. Q5(d)

    Summer 2024 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(d): to show that the expected mean gradient is −1 and that the 2  a expected ln(B) intercept is ln    I 0 . [2] 2 

  11. Q5(e)

    Summer 2024 · Unit 4

    3 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(e): . [3] 2 a 

  12. Q5(f)

    Summer 2024 · Unit 4

    5 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(f): Calculate the current in the wire along with its absolute uncertainty. [5]

  13. Q5(g)

    Summer 2024 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2024 Unit 4, question 5(g): a. 600 B /μT 500 400 300 200 100 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1 a / cm−1 Explain briefly why Michael’s log graph is more suitable than Bethan’s graph for this

  14. Q4(a)(i)

    Summer 2023 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(a)(i): Explain briefly why the magnetic force must be upward on the part XY of the wire. [2]

  15. Q4(a)(ii)

    Summer 2023 · Unit 4

    2 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(a)(ii): On the diagram, indicate which is the North pole of the magnet, and state below which rule you used to obtain your answer. [2]

  16. Q4(a)(iii)

    Summer 2023 · Unit 4

    1 mark4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(a)(iii): Explain why the vertical parts of the wire have no effect on the reading displayed by the electronic balance. [1]

  17. Q4(b)(i)

    Summer 2023 · Unit 4

    4 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(b)(i): Complete the table and plot the two missing points on the graph. [4] Magnetic force / 10–3 N Length of XY / cm Balance reading / g 1.0 0.56 5.5 2.0 1.22 3.0 1.7

  18. Q4(b)(ii)

    Summer 2023 · Unit 4

    3 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(b)(ii): The region of uniform magnetic field between the poles of the magnet is of length 5 cm only. Evaluate whether or not Bronwen has drawn the line of best fit corr

  19. Q4(b)(iii)

    Summer 2023 · Unit 4

    5 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 4(b)(iii): Determine the magnetic flux density, B, of the uniform magnetic field between the poles of the magnet and quote it to an appropriate number of significant figur

  20. Q5(b)

    Summer 2023 · Unit 4

    6 marks4.4 Magnetic fields
    The whole paper ↗
    Summer 2023 Unit 4, question 5(b): Explain how a Hall voltage arises in a Hall probe, how it is measured and how this can be used to measure the magnetic flux density. A diagram should be include
All 41 questions on Magnetic fields, as a list
  1. Summer 2025, Unit 4, Q4(a)(i) (3 marks): Explain why a valid equation for the motion of the proton while inside a dee is: mω2r = Bqω r where m is the mass of the proton, ω is the angular velocity of th
  2. Summer 2025, Unit 4, Q4(a)(ii) (3 marks): Hence or otherwise, calculate the magnetic flux density. [3]
  3. Summer 2025, Unit 4, Q4(b) (2 marks): Each time the proton crosses between the dees, it is accelerated by a pd of 1.2 kV. Calculate the increase in kinetic energy in J of the proton each time it cro
  4. Summer 2025, Unit 4, Q4(c)(i) (2 marks): Show that this happens when the proton has a kinetic energy of approximately 1 pJ. [2]
  5. Summer 2025, Unit 4, Q4(c)(ii) (2 marks): The proton is accelerated twice per cycle. Determine whether the proton spends more than a millisecond in the cyclotron if it is accelerated from rest. [2]
  6. Summer 2025, Unit 4, Q4(d) (2 marks): ‘All money spent on particle accelerators is wasted!’ Discuss this statement briefly. [2]
  7. Summer 2024, Unit 4, Q5(a) (1 mark): is plotted using the corrected B -field. Measured Corrected a / m ln (a / m) ln (B / T) B -field / T B -field, B / T 0.010 0.000 529 0.000 499 −4.61 −7.60 0.020
  8. Summer 2024, Unit 4, Q5(b) (3 marks): Complete the table above and plot the missing point on the graph opposite (no error bars are required). [3]
  9. Summer 2024, Unit 4, Q5(c) (2 marks): The gradient of the steepest line is −1.03. Calculate the gradient of the least steep line. [2] ln (a / m) _ 5.00 _ 4.50 _ 4.00 _ 3.50 _ 3.00 _ 2.50 _ 2.00 _ 1.
  10. Summer 2024, Unit 4, Q5(d) (2 marks): to show that the expected mean gradient is −1 and that the 2  a expected ln(B) intercept is ln    I 0 . [2] 2 
  11. Summer 2024, Unit 4, Q5(e) (3 marks): . [3] 2 a 
  12. Summer 2024, Unit 4, Q5(f) (5 marks): Calculate the current in the wire along with its absolute uncertainty. [5]
  13. Summer 2024, Unit 4, Q5(g) (2 marks): a. 600 B /μT 500 400 300 200 100 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1 a / cm−1 Explain briefly why Michael’s log graph is more suitable than Bethan’s graph for this
  14. Summer 2023, Unit 4, Q4(a)(i) (2 marks): Explain briefly why the magnetic force must be upward on the part XY of the wire. [2]
  15. Summer 2023, Unit 4, Q4(a)(ii) (2 marks): On the diagram, indicate which is the North pole of the magnet, and state below which rule you used to obtain your answer. [2]
  16. Summer 2023, Unit 4, Q4(a)(iii) (1 mark): Explain why the vertical parts of the wire have no effect on the reading displayed by the electronic balance. [1]
  17. Summer 2023, Unit 4, Q4(b)(i) (4 marks): Complete the table and plot the two missing points on the graph. [4] Magnetic force / 10–3 N Length of XY / cm Balance reading / g 1.0 0.56 5.5 2.0 1.22 3.0 1.7
  18. Summer 2023, Unit 4, Q4(b)(ii) (3 marks): The region of uniform magnetic field between the poles of the magnet is of length 5 cm only. Evaluate whether or not Bronwen has drawn the line of best fit corr
  19. Summer 2023, Unit 4, Q4(b)(iii) (5 marks): Determine the magnetic flux density, B, of the uniform magnetic field between the poles of the magnet and quote it to an appropriate number of significant figur
  20. Summer 2023, Unit 4, Q5(b) (6 marks): Explain how a Hall voltage arises in a Hall probe, how it is measured and how this can be used to measure the magnetic flux density. A diagram should be include
  21. Summer 2022, Unit 4, Q1(a)(i) (3 marks): Lindsey calculates that a current of 3.57 A will produce a magnetic flux density of 0.121 T inside the long solenoid shown. Determine whether or not she is corr
  22. Summer 2022, Unit 4, Q1(a)(ii) (1 mark): State how the magnetic flux density inside the solenoid can be increased greatly without changing the current or the number of turns per unit length. [1]
  23. Summer 2022, Unit 4, Q6(a)(i) (4 marks): By considering the forces acting on free electrons passing through the wafer, explain why a Hall voltage is measured on the voltmeter shown. [4]
  24. Summer 2022, Unit 4, Q6(a)(ii) (3 marks): given by: VH = Bvd where B is the magnetic flux density, d is the width of the wafer and v is the drift velocity. [3]
  25. Summer 2022, Unit 4, Q6(a)(iii) (2 marks): Catrin states that her measured Hall voltage of 68.0 nV is consistent with a drift velocity of approximately 0.07mms–1. Determine whether, or not, she is correc
  26. Summer 2022, Unit 4, Q6(a)(iv) (3 marks): Calculate the number of free electrons per unit volume for the metal. [3]
  27. Summer 2022, Unit 4, Q6(b) (2 marks): After repeating the same experiment on a different metal, Catrin obtains a value of (5.85 ± 0.19) × 1028 m–3, for the number of free electrons per unit volume.
  28. Summer 2019, Unit 4, Q4(a) (3 marks): The current in a long wire is 290 A and is too great to be measured by an ammeter. Explain how you could use a Hall probe, calibrated in tesla (T), to determine
  29. Summer 2019, Unit 4, Q4(b) (4 marks): Another long wire carrying the same large current is placed parallel to the original wire as shown. Calculate the force per unit length on each wire also statin
  30. Summer 2019, Unit 4, Q4(c)(i) (4 marks): Tirion claims that an electron halfway between the wires, travelling at a speed of 2.9 × 107 m s–1 parallel to the wires will perform perfect circular motion be
  31. Summer 2019, Unit 4, Q4(c)(ii) (2 marks): Sketch the motion of the electron. [2] 290 A 5.0 cm 290 A
  32. Summer 2019, Unit 4, Q4(d) (5 marks): Suppose that an electron travels in a region with a magnetic field and an electric field due to two parallel metal plates as shown below. Deduce whether or not
  33. Summer 2018, Unit 4, Q4(a) (4 marks): Calculate the mean value of the gradient along with its percentage uncertainty. [4]
  34. Summer 2018, Unit 4, Q4(b) (3 marks): Calculate the number of turns in the solenoid along with its absolute uncertainty. The percentage uncertainty in the length of the solenoid is 0.4 %. [3]
  35. Summer 2018, Unit 4, Q4(c)(i) (4 marks): The solenoid manufacturer states that there are exactly 5 000 turns in the solenoid. Evaluate the accuracy of your value obtained in part (b) and whether or not
  36. Summer 2018, Unit 4, Q4(c)(ii) (2 marks): Suggest a reason for the disagreement between the manufacturer’s stated value (5 000 turns) and your value calculated in part (b). Suggest how the experimental
  37. Summer 2017, Unit 4, Q4(a)(i) (3 marks): Explain why the reading on the balance is negative for the direction of current and magnetic field shown in the diagram. [3] The student’s results are plotted o
  38. Summer 2017, Unit 4, Q4(a)(ii) (3 marks): and its percentage uncertainty. [3]
  39. Summer 2017, Unit 4, Q4(a)(iii) (4 marks): The length of wire in the uniform magnetic field is (8.0 ± 0.5) cm. Determine a value for the magnetic field strength and its absolute uncertainty, stating both
  40. Summer 2017, Unit 4, Q4(b)(i) (3 marks): Explain how the Hall voltage arises in the Hall probe shown. [3]
  41. Summer 2017, Unit 4, Q4(b)(ii) (6 marks): Discuss the effectiveness of the experiment in part (a) for confirming the relationship F=BIℓ and measuring the magnetic field strength, compared with using the

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