Lesson 3.7.5.5

3.7.5.5 Alternating currents Quiz: AQA Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.5.5, Alternating currents: 20 multiple choice questions for the AQA Physics (7408), Unit 7: Fields and their consequences (A-level only), written with Revision Ninja.

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The 20 questions

  1. What is the root mean square (rms) value of an alternating current?

    • the average of the current over one full cycle, which is zero for a sine wave
    • the value of the current at the mid-point of each half cycle
    • the steady direct current that dissipates the same power in a resistor
    • the maximum value reached by the current in each cycle

  2. For a sinusoidal current with peak value I0, which expression gives the rms current?

    • I0 x sqrt(2)
    • I0 / sqrt(2)
    • 2 I0 / pi
    • I0 / 2

  3. What is the peak-to-peak value of a sinusoidal waveform?

    • equal to the peak value
    • twice the peak value
    • the square root of two times the peak value
    • half the peak value

  4. The mains supply in the UK has an rms voltage of 230 V. What is its peak voltage?

    • 460 V
    • 163 V
    • 325 V
    • 230 V

  5. The mains supply has an rms voltage of 230 V. What is its peak-to-peak voltage?

    • 920 V
    • 460 V
    • 325 V
    • 650 V

  6. A sinusoidal current has a peak value of 4.0 A. What is its rms value?

    • 2.8 A
    • 5.7 A
    • 4.0 A
    • 1.4 A

  7. A sinusoidal voltage has an rms value of 12 V. What is its peak value?

    • 24 V
    • 17 V
    • 8.5 V
    • 12 V

  8. A 10 ohm resistor is connected across a sinusoidal supply of rms voltage 12 V. What is the average power dissipated?

    • 28.8 W
    • 7.2 W
    • 14.4 W
    • 1.44 W

  9. An oscilloscope shows one complete cycle of a waveform occupying 20 ms. What is its frequency?

    • 500 Hz
    • 0.050 Hz
    • 20 Hz
    • 50 Hz

  10. On an oscilloscope, one full cycle spans 8.0 divisions at a time base of 5.0 ms per division. What is the frequency?

    • 5 Hz
    • 200 Hz
    • 25 Hz
    • 40 Hz

  11. A sinusoidal source has a peak voltage of 6.0 V and is connected across a 2.0 ohm resistor. What is the average power dissipated?

    • 9.0 W
    • 4.5 W
    • 18 W
    • 36 W

  12. Why is the average of a sinusoidal alternating current over one whole cycle zero?

    • The positive and negative halves of the cycle cancel each other exactly
    • The current stays at its peak value for the whole cycle
    • The current is zero for half of every cycle
    • The frequency is too high for the average to be measured

  13. A d.c. supply produces the same heating in a resistor as a sinusoidal current of peak value 2.0 A. What is the d.c. current?

    • 1.0 A
    • 2.0 A
    • 1.4 A
    • 2.8 A

  14. A sine wave on an oscilloscope has a period of 4.0 ms. What is its frequency?

    • 4 Hz
    • 250 Hz
    • 500 Hz
    • 125 Hz

  15. When an oscilloscope is set to ac coupling, which part of the signal is blocked?

    • the high-frequency noise above 1 kHz
    • the dc component, so only the alternating part is displayed
    • the time base setting
    • the peak value of the signal

  16. A 2.0 kW appliance runs from a 230 V rms mains supply. What is the rms current it draws?

    • 8.7 A
    • 12 A
    • 0.12 A
    • 4.3 A

  17. A 325 V peak supply is across a 100 ohm resistor. What is the average power dissipated?

    • 530 W
    • 3.3 kW
    • 1060 W
    • 265 W

  18. A sine wave has a peak-to-peak value of 10 V. What is its rms value?

    • 5.0 V
    • 3.5 V
    • 2.5 V
    • 7.1 V

  19. Why is the rms value used for mains voltage rather than the average value?

    • Because power depends on the square of the current or voltage, so the rms value gives the correct heating effect
    • Because the average is always zero, so it cannot be used for anything
    • Because rms values are easier to read on a standard meter than other values
    • Because the average value is always larger than the peak value

  20. A 6 V, 3 W lamp runs correctly on an rms supply. What peak voltage is needed for the same brightness on a sine supply?

    • 6.0 V
    • 4.2 V
    • 12 V
    • 8.5 V

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