Lesson 7.6.1

7.6.1 Alternating current and root-mean-square values Quiz: Pearson Edexcel Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 7.6.1, Alternating current and root-mean-square values: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 7: Electric and Magnetic Fields, 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 value of direct current that would dissipate the same mean power in a resistor
    • The value of the current at the instant the voltage crosses zero
    • The average value of the current over one half-cycle, with no regard to direction
    • The maximum instantaneous value reached by the current in each cycle

  2. What is the peak value of an alternating voltage?

    • The voltage measured from the most negative point to the most positive point
    • The average of the voltage over a complete cycle, including its sign
    • The maximum value of the voltage reached during each cycle, measured from zero
    • The value of the voltage at the instant it reverses direction

  3. What is the period of an alternating voltage?

    • The time taken to complete one full cycle
    • The time between successive zero crossings in the same direction only
    • The number of cycles completed in one second
    • The time taken for the voltage to reach its peak value from zero

  4. For a sinusoidal alternating voltage, which equation relates rms voltage to peak voltage?

    • V_rms = 2 V0
    • V_rms = V0 / 2
    • V_rms = V0 sqrt(2)
    • V_rms = V0 / sqrt(2)

  5. The peak-to-peak voltage of an alternating supply is 2 V0. If the peak voltage is 16 V, what is the peak-to-peak voltage?

    • 23 V
    • 16 V
    • 8.0 V
    • 32 V

  6. The mains rms voltage is 230 V. What is the peak voltage?

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

  7. An alternating current has a peak value of 5.0 A. What is its rms value?

    • 7.1 A
    • 5.0 A
    • 3.5 A
    • 2.5 A

  8. An alternating supply has a frequency of 50 Hz. What is its period?

    • 0.050 s
    • 0.20 s
    • 0.0020 s
    • 0.020 s

  9. An alternating voltage has a steady rms value of 12 V across a 100 ohm resistor. What is the mean power dissipated?

    • 14 W
    • 2.9 W
    • 0.12 W
    • 1.4 W

  10. An alternating voltage has a peak value of 16 V. What is its rms value?

    • 16 V
    • 8.0 V
    • 11 V
    • 23 V

  11. A direct voltage of 9.0 V produces the same heating in a resistor as an alternating voltage. What is the peak value of that alternating voltage?

    • 4.5 V
    • 12.7 V
    • 9.0 V
    • 18 V

  12. A mains supply has frequency 50 Hz. What is its angular frequency?

    • 50 rad s^-1
    • 157 rad s^-1
    • 25 rad s^-1
    • 314 rad s^-1

  13. A resistor of resistance 50 ohm carries an alternating current with peak value 2.0 A. What is the mean power dissipated?

    • 141 W
    • 100 W
    • 200 W
    • 50 W

  14. An alternating voltage has a frequency of 0.5 kHz. What is the time between two successive peaks?

    • 2 ms
    • 0.5 ms
    • 5 ms
    • 20 ms

  15. The peak voltage across a resistor is doubled. How does the mean power dissipated in the resistor change?

    • It is unchanged
    • It halves
    • It quadruples
    • It doubles

  16. An alternating voltage of rms value 6.0 V is applied across a 12 ohm resistor. What is the peak current?

    • 0.71 A
    • 0.35 A
    • 0.50 A
    • 1.0 A

  17. A 240 V rms mains lamp dissipates a mean power of 60 W. What is its resistance?

    • 4.0 ohm
    • 1.4 x 10^4 ohm
    • 240 ohm
    • 9.6 x 10^2 ohm

  18. The rms value of a sinusoidal voltage is defined as which quantity?

    • The square root of the mean value of the square of the voltage over a complete cycle
    • The mean of the voltage over a complete cycle, with no squaring
    • The maximum voltage multiplied by the frequency of the supply
    • The mean of the squares of the peak and minimum voltages only

  19. A sinusoidal voltage V = V0 sin(omega t) has a frequency of 50 Hz. How long does it take to rise from zero to its first maximum?

    • 10 ms
    • 2.5 ms
    • 5 ms
    • 20 ms

  20. A student computes the mean power in a resistor by multiplying peak voltage by peak current. Which response is correct?

    • The student is wrong: the mean power is V0 I0 / 2, which equals Vrms Irms
    • The student is wrong, because mean power is V0 I0 multiplied by pi
    • The student is right, but only if the resistor has a reactance
    • The student is right, because peak values give the correct mean power directly

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