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Alternating currents: Eduqas A‑Level Physics questions

Every Eduqas A-Level Physics exam question on 3.A Alternating currents, 2016–2025, with its mark scheme and examiner’s report.

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1,592 questions

  1. Q9(a)(i)

    June 2025 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(a)(i): State two changes that could be made to the design of the coil in order to increase the peak emf (for the same angular velocity and magnetic field). [2]

  2. Q9(a)(ii)

    June 2025 · Component 3

    1 mark3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(a)(ii): Write an equation for the peak emf induced in a rotating coil. [1]

  3. Q9(a)(iii)

    June 2025 · Component 3

    5 marks3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(a)(iii): The sinusoidal emf produced by the coil rotating in the uniform magnetic field has rms value of 4.2 V and a frequency of 50.0 Hz. The coil is connected to the i

  4. Q9(b)

    June 2025 · Component 3

    3 marks3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(b): Sophie builds the following circuit. She claims that the rms voltage output, Vout, will be smaller at higher frequencies. Evaluate Sophie’s claim and state whet

  5. Q9(c)(i)

    June 2025 · Component 3

    1 mark3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(c)(i): State the mean power dissipated in the inductor. [1]

  6. Q9(c)(ii)

    June 2025 · Component 3

    4 marks3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(c)(ii): When the frequency of Vin is equal to 15 kHz, the rms current is at its maximum. Determine the value of the inductance of the inductor. [4]

  7. Q9(c)(iii)

    June 2025 · Component 3

    3 marks3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(c)(iii): Calculate the Q factor of the circuit. [3]

  8. Q9(c)(iv)

    June 2025 · Component 3

    1 mark3.A Alternating currents
    The whole paper ↗
    June 2025 Component 3, question 9(c)(iv): State the effect of increasing the Q factor on the resonance curve. [1]

  9. Q9(a)(i)

    June 2024 · Component 3

    3 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(a)(i): Calculate the mean power dissipated in the resistor. [3]

  10. Q9(a)(ii)

    June 2024 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(a)(ii): Calculate the energy dissipated per cycle in the resistor. [2]

  11. Q9(a)(iii)

    June 2024 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(a)(iii): Determine the number of times per second the instantaneous power dissipation in the resistor reaches a maximum. [2]

  12. Q9(b)

    June 2024 · Component 3

    1 mark3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(b): The same alternating pd is now connected across a different component, X, and the following graphs are produced. 5 pd / V 0 0 Time / s 0.01 0.02 0.03 0.04 – 5 5

  13. Q9(c)(i)

    June 2024 · Component 3

    3 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(c)(i): Use a labelled phasor diagram to show that the impedance, Z, of the circuit is given by: [3] Z  X 2  R 2 L

  14. Q9(c)(ii)

    June 2024 · Component 3

    4 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(c)(ii): Morgan knows that no power is dissipated in an inductor with zero resistance. He therefore claims that adding the inductor will not affect the mean power dissip

  15. Q9(d)(i)

    June 2024 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(d)(i): Calculate the rms current in the circuit. [2]

  16. Q9(d)(ii)

    June 2024 · Component 3

    3 marks3.A Alternating currents
    The whole paper ↗
    June 2024 Component 3, question 9(d)(ii): Hence, calculate the value of the capacitor. [3]

  17. Q11(a)(i)

    June 2023 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2023 Component 3, question 11(a)(i): Show, in clear steps, that the resonance frequency, f0, of the circuit is given by: [2] 1 f0 = π 2 LC

  18. Q11(a)(ii)

    June 2023 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2023 Component 3, question 11(a)(ii): Calculate the maximum possible resonance frequency for the circuit. [2]

  19. Q11(a)(iii)

    June 2023 · Component 3

    2 marks3.A Alternating currents
    The whole paper ↗
    June 2023 Component 3, question 11(a)(iii): Explain why the maximum rms current in this circuit is approximately 5 A. [2]

  20. Q11(b)(i)

    June 2023 · Component 3

    4 marks3.A Alternating currents
    The whole paper ↗
    June 2023 Component 3, question 11(b)(i): Use a labelled phasor diagram to explain why the impedance of the circuit, Z, is given by: [4] R2 2 Z = + XC
All 57 questions on Alternating currents, as a list
  1. June 2025, Component 3, Q9(a)(i) (2 marks): State two changes that could be made to the design of the coil in order to increase the peak emf (for the same angular velocity and magnetic field). [2]
  2. June 2025, Component 3, Q9(a)(ii) (1 mark): Write an equation for the peak emf induced in a rotating coil. [1]
  3. June 2025, Component 3, Q9(a)(iii) (5 marks): The sinusoidal emf produced by the coil rotating in the uniform magnetic field has rms value of 4.2 V and a frequency of 50.0 Hz. The coil is connected to the i
  4. June 2025, Component 3, Q9(b) (3 marks): Sophie builds the following circuit. She claims that the rms voltage output, Vout, will be smaller at higher frequencies. Evaluate Sophie’s claim and state whet
  5. June 2025, Component 3, Q9(c)(i) (1 mark): State the mean power dissipated in the inductor. [1]
  6. June 2025, Component 3, Q9(c)(ii) (4 marks): When the frequency of Vin is equal to 15 kHz, the rms current is at its maximum. Determine the value of the inductance of the inductor. [4]
  7. June 2025, Component 3, Q9(c)(iii) (3 marks): Calculate the Q factor of the circuit. [3]
  8. June 2025, Component 3, Q9(c)(iv) (1 mark): State the effect of increasing the Q factor on the resonance curve. [1]
  9. June 2024, Component 3, Q9(a)(i) (3 marks): Calculate the mean power dissipated in the resistor. [3]
  10. June 2024, Component 3, Q9(a)(ii) (2 marks): Calculate the energy dissipated per cycle in the resistor. [2]
  11. June 2024, Component 3, Q9(a)(iii) (2 marks): Determine the number of times per second the instantaneous power dissipation in the resistor reaches a maximum. [2]
  12. June 2024, Component 3, Q9(b) (1 mark): The same alternating pd is now connected across a different component, X, and the following graphs are produced. 5 pd / V 0 0 Time / s 0.01 0.02 0.03 0.04 – 5 5
  13. June 2024, Component 3, Q9(c)(i) (3 marks): Use a labelled phasor diagram to show that the impedance, Z, of the circuit is given by: [3] Z  X 2  R 2 L
  14. June 2024, Component 3, Q9(c)(ii) (4 marks): Morgan knows that no power is dissipated in an inductor with zero resistance. He therefore claims that adding the inductor will not affect the mean power dissip
  15. June 2024, Component 3, Q9(d)(i) (2 marks): Calculate the rms current in the circuit. [2]
  16. June 2024, Component 3, Q9(d)(ii) (3 marks): Hence, calculate the value of the capacitor. [3]
  17. June 2023, Component 3, Q11(a)(i) (2 marks): Show, in clear steps, that the resonance frequency, f0, of the circuit is given by: [2] 1 f0 = π 2 LC
  18. June 2023, Component 3, Q11(a)(ii) (2 marks): Calculate the maximum possible resonance frequency for the circuit. [2]
  19. June 2023, Component 3, Q11(a)(iii) (2 marks): Explain why the maximum rms current in this circuit is approximately 5 A. [2]
  20. June 2023, Component 3, Q11(b)(i) (4 marks): Use a labelled phasor diagram to explain why the impedance of the circuit, Z, is given by: [4] R2 2 Z = + XC
  21. June 2023, Component 3, Q11(b)(ii) (2 marks): Hence show that: [2] 1 Z2 = + R2 ω2 C2
  22. June 2023, Component 3, Q11(b)(iii) (5 marks): Using the circuit, Daniel determines Z for a number of different values of ω and plots a graph of Z2 against 1 ω2 . 14.0 Z2 / Ω2 12.0 10.0 8.0 6.0 4.0 2.0 0 0 5
  23. June 2023, Component 3, Q11(b)(iv) (3 marks): While carrying out the investigation, Daniel notices that the pd across the resistor, VR, is small at low frequencies and approaches the supply pd at high frequ
  24. Autumn 2021, Component 3, Q9(b)(i) (1 mark): Show that the resonance frequency of the circuit above is approximately 10 000 Hz. [1]
  25. Autumn 2021, Component 3, Q9(b)(ii) (1 mark): Explain why the maximum rms current is approximately 50 mA. [1]
  26. Autumn 2021, Component 3, Q9(b)(iii) (3 marks): Show that the rms current in the circuit is approximately 17 mA when the frequency is 16 kHz. [3]
  27. Autumn 2021, Component 3, Q9(b)(iv) (3 marks): Use the results of parts (i), (ii) and (iii) to sketch a graph of rms current against frequency for the circuit on the axes provided. [3] 120 rms current / mA 1
  28. Autumn 2021, Component 3, Q9(c) (5 marks): Caitlin claims that the graph below shows the variation of rms current with frequency for the RCL circuit shown (the same circuit as in part (b) but with the re
  29. Autumn 2020, Component 3, Q11(a) (3 marks): With the aid of a phasor diagram, explain why the impedance of an RCL circuit is given by: [3] 2 + R2 ( ) Z = XL − XC
  30. Autumn 2020, Component 3, Q11(b)(i) (3 marks): Show that the combined magnitude of the reactance of the inductor and capacitor is the same (to 3 s.f.) as the resistance of the resistor when the frequency is
  31. Autumn 2020, Component 3, Q11(b)(ii) (3 marks): Hence, calculate the rms current in the circuit when the frequency is 4 150 Hz. [3]
  32. Autumn 2020, Component 3, Q11(b)(iii) (1 mark): Calculate (or state) the phase angle between the applied pd and the current when the frequency is 4 150 Hz. [1]
  33. Autumn 2020, Component 3, Q11(b)(iv) (3 marks): The resonance frequency of the RCL circuit is approximately 9 800 Hz. By sketching a graph of rms current against frequency, explain why there is a second highe
  34. Autumn 2020, Component 3, Q11(b)(v) (2 marks): This second frequency occurs when the magnitude of the reactances of the inductor and capacitor are reversed from those in part (b)(i). Use this information to
  35. Autumn 2020, Component 3, Q11(c) (5 marks): Robyn is required to produce a wave trace on an oscilloscope for an a.c. power supply of frequency 3.0 kHz and rms pd 0.60 V. Deduce whether or not the settings
  36. June 2019, Component 3, Q11(a) (3 marks): Derive the expression for the resonance frequency, f0, of a series RCL circuit. [3] 1 f0 = 2π LC
  37. June 2019, Component 3, Q11(b)(i) (1 mark): Calculate the rms current at the resonance frequency (f0). [1]
  38. June 2019, Component 3, Q11(b)(ii) (4 marks): Calculate the rms current at twice the resonance frequency (2f0). [4]
  39. June 2019, Component 3, Q11(b)(iii) (2 marks): Calculate the Q factor of the RCL circuit. [2]
  40. June 2019, Component 3, Q11(b)(iv) (3 marks): Sketch a graph of the rms current in the RCL circuit versus applied frequency of the a.c. supply on the axes provided. Label this graph 28 Ω. [3] rms current /
  41. June 2019, Component 3, Q11(b)(v) (2 marks): The 28 Ω resistor is replaced by a 56 Ω resistor. On the same axes, sketch and label a second graph showing the rms current versus frequency for the new circuit
  42. June 2019, Component 3, Q11(c) (5 marks): Morgan claims that the rms output pd (Vout) in the following circuit is greater than 4.25 V when the frequency is greater than 82.5 Hz but less than 4.25 V belo
  43. June 2018, Component 3, Q11(a)(i) (2 marks): Calculate the rms pd of the oscilloscope trace shown. [2]
  44. June 2018, Component 3, Q11(a)(ii) (2 marks): Calculate the frequency of the oscilloscope trace shown. [2]
  45. June 2018, Component 3, Q11(b)(i) (2 marks): Use Faraday’s Law to explain why the peak emf induced in the coil is proportional to the angular velocity of rotation of the coil. [2]
  46. June 2018, Component 3, Q11(b)(ii) (2 marks): Use Faraday’s Law to explain why the emf induced in the coil depends on the angle, θ. [2]
  47. June 2018, Component 3, Q11(c)(i) (2 marks): In the following LCR circuit, explain why the rms resonance current is 125 mA. [2] variable frequency a.c. supply Vrms = 15 V 120 Ω 24 mH 4.2 nF
  48. June 2018, Component 3, Q11(c)(ii) (2 marks): Calculate the resonance frequency of the circuit. [2]
  49. June 2018, Component 3, Q11(c)(iii) (3 marks): Show that the rms current is 42 mA when the frequency of the supply is 17 kHz. [3]
  50. June 2018, Component 3, Q11(c)(iv) (5 marks): Alistair claims that the mean power dissipation in the circuit at 17 kHz is: P = IrmsVrms = 0.042 × 15 = 0.63 W Another student Michonne states that the correct
  51. June 2017, Component 3, Q10(a)(i) (2 marks): the rms current; [2]
  52. June 2017, Component 3, Q10(a)(ii) (2 marks): the resistance of the toaster. [2]
  53. June 2017, Component 3, Q10(b) (5 marks): Helen claims that the following circuit will have a minimum impedance of 68 Ω when the frequency is very low but that the impedance will be extremely large at h
  54. June 2017, Component 3, Q10(c)(i) (2 marks): Explain why the rms current at resonance of the following circuit is approximately 700 mA. [2] variable frequency a.c. supply Vrms = 12 V 18 Ω 5.2 mH 13.5 μF
  55. June 2017, Component 3, Q10(c)(ii) (2 marks): Show that the resonance frequency (f0) is approximately 600 Hz. [2]
  56. June 2017, Component 3, Q10(c)(iii) (4 marks): Calculate the rms current when the frequency of the supply is increased to 1.5 f0 [4]
  57. June 2017, Component 3, Q10(c)(iv) (3 marks): Explain why the rms current is the same when the frequency is decreased to f0 (iv) 1.5 . [3]

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