Lesson 3.7.4.3

3.7.4.3 Energy stored by a capacitor Quiz: AQA Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 3.7.4.3, Energy stored by a capacitor: 20 multiple choice questions for the AQA Physics (7408), Unit 7: Fields and their consequences (A-level only), written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. What does the area under a graph of charge against pd for a capacitor represent?

    • The capacitance of the capacitor
    • The resistance of the circuit connected to it
    • The energy stored by the capacitor
    • The charge on the capacitor

  2. Which expression gives the energy stored in a capacitor in terms of Q and C?

    • E = 2Q^2/C
    • E = Q^2 C/2
    • E = Q C^2/2
    • E = Q^2/(2C)

  3. A 100 microfarad capacitor is charged to 20 V. How much energy is stored?

    • 0.20 J
    • 2.0 J
    • 0.020 J
    • 0.0020 J

  4. A 470 microfarad capacitor is charged to 12 V. How much energy does it store?

    • 34 mJ
    • 340 mJ
    • 68 mJ
    • 17 mJ

  5. A capacitor holds 2.0 mC of charge at a pd of 50 V. What energy is stored?

    • 0.025 J
    • 0.10 J
    • 0.20 J
    • 0.050 J

  6. A capacitor with fixed capacitance has its pd doubled. By what factor does its stored energy change?

    • 1/4 times
    • unchanged
    • 2 times
    • 4 times

  7. Why is the energy stored in a capacitor given by (1/2)QV rather than QV?

    • Because the pd rises in proportion to the charge added, so the average pd during charging is V/2
    • Because half the charge leaks away from the plates during charging
    • Because the capacitance halves as the capacitor charges up
    • Because only the positive plate stores energy while the negative plate stores none

  8. A camera flash capacitor of 2200 microfarad is charged to 330 V. Roughly how much energy does it store?

    • about 120 J
    • about 240 J
    • about 60 J
    • about 12 J

  9. A capacitor stores 0.40 mC at a pd of 0.10 V. Which expression gives its energy?

    • E = 0.5 x 0.40 x 10^-3 x 0.10^2 = 2.0 x 10^-6 J
    • E = 0.40 x 10^-3 x 0.10 = 4.0 x 10^-5 J
    • E = 0.5 x 0.40 x 10^-3 / 0.10 = 2.0 x 10^-3 J
    • E = 0.5 x 0.40 x 10^-3 x 0.10 = 2.0 x 10^-5 J

  10. A capacitor stores 0.20 mJ of energy at a pd of 5.0 V. What is its capacitance?

    • 10 microfarad
    • 20 microfarad
    • 40 microfarad
    • 2.0 microfarad

  11. A capacitor is charged to a pd of 12 V and stores 36 mJ of energy. What is its capacitance?

    • 0.50 mF
    • 0.25 mF
    • 5.0 mF
    • 2.0 mF

  12. A capacitor's pd falls to half its initial value. What fraction of its original stored energy remains?

    • three quarters
    • one quarter
    • one eighth
    • one half

  13. A 4700 microfarad capacitor is charged to 25 V and then discharged through a motor. How much energy is delivered?

    • 1.5 J
    • 0.37 J
    • 2.9 J
    • 0.73 J

  14. A capacitor stores 0.50 J of energy with charge 0.10 C on its plates. What is the pd across it?

    • 5.0 V
    • 0.20 V
    • 20 V
    • 10 V

  15. A capacitor has charge 0.20 C and capacitance 0.010 F. How much energy is stored?

    • 0.20 J
    • 4.0 J
    • 2.0 J
    • 1.0 J

  16. A capacitor holds energy E0 at charge Q. Its capacitance is halved while its charge stays the same. What is the new energy?

    • E0/2
    • 4E0
    • 2E0
    • E0

  17. A capacitor of fixed charge has its plates pulled apart so that the separation doubles. How does the stored energy change?

    • It quadruples, because the separation has doubled
    • It is unchanged, because the charge is fixed
    • It doubles, because work must be done against the attraction of the plates
    • It halves, because the capacitance has halved

  18. A capacitor has a straight-line Q-V graph with gradient 2.0 mF per V. It is charged to 5.0 V. How much energy is stored?

    • 0.25 J
    • 0.0125 J
    • 0.050 J
    • 0.025 J

  19. A 100 microfarad capacitor is charged through a resistor from a 12 V supply. What fraction of the energy drawn from the supply is dissipated in the resistor?

    • one quarter
    • one half
    • all of it
    • three quarters

  20. A 1.0 mF capacitor is charged to 30 V. How much energy is stored?

    • 0.90 J
    • 0.015 J
    • 4.5 J
    • 0.45 J

All AQA Physics quizzes