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

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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.

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The 20 questions

  1. What quantity is represented by the area under a charge against potential difference graph for a capacitor?

    • Capacitance
    • Electric current
    • Stored energy
    • Time constant

  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 energy stored in a capacitor equal to half of charge multiplied by potential difference?

    • Average pd is V/2
    • Charge is halved
    • Voltage remains constant
    • Capacitance decreases linearly

  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. An isolated capacitor has its plate separation doubled. What happens to the stored energy?

    • Remains constant
    • Quadruples
    • Doubles
    • Halves

  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

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