Lesson 6.1.3

6.1.3 Charging and discharging capacitors Quiz: OCR Physics, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.1.3, Charging and discharging capacitors: 20 multiple choice questions for the OCR Physics (H156), Unit 5: Particles and medical physics, written with Revision Ninja.

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The 20 questions

  1. What is the SI unit for the time constant of a capacitor-resistor circuit?

    • Second
    • Farad
    • Ohm
    • Coulomb

  2. Which expression represents the energy W stored in a capacitor with charge Q and voltage V?

    • 0.5 Q / V
    • 0.5 Q V
    • Q V
    • Q V^2

  3. What is the time constant tau for a circuit containing capacitance C and resistance R?

    • C / R
    • 1 / CR
    • CR
    • R / C

  4. What is the time constant of a circuit with a 100 microfarad capacitor and 10 kilohm resistor?

    • 0.1 s
    • 1.0 s
    • 100 s
    • 10 s

  5. What percentage of initial charge remains on a discharging capacitor after one time constant?

    • 50%
    • 63%
    • 33%
    • 37%

  6. What property describes a graph where charge decreases by equal factors in equal time intervals?

    • Constant gradient property
    • Inverse square property
    • Linear property
    • Constant-ratio property

  7. Which formula gives the charge Q on a discharging capacitor after time t?

    • Q = Q0 (1 - e^(-t/CR))
    • Q = Q0 e^(-t/CR)
    • Q = Q0 / CR
    • Q = Q0 e^(t/CR)

  8. Which equation gives the charge Q on a capacitor being charged from zero over time t?

    • Q = Q0 (1 + e^(-t/CR))
    • Q = Q0 e^(t/CR)
    • Q = Q0 (1 - e^(-t/CR))
    • Q = Q0 e^(-t/CR)

  9. What is the gradient of a graph of natural log of charge against time for a discharging capacitor?

    • 1 / CR
    • -1 / CR
    • CR
    • -CR

  10. A capacitor stores 4.0 millijoules of energy when charged to 10 volts. What is its capacitance?

    • 40 microfarads
    • 0.8 microfarads
    • 800 microfarads
    • 80 microfarads

  11. In spreadsheet modelling of a discharging capacitor, what expression gives the rate of change of charge?

    • - Q / CR
    • Q / t
    • - Q CR
    • - CR / Q

  12. How many time constants does it take for a charging capacitor to reach 63 percent charge?

    • 1
    • 2
    • 0.63
    • 3

  13. What is the energy stored in a 200 microfarad capacitor charged to a potential difference of 12 volts?

    • 0.0288 J
    • 0.0144 J
    • 0.144 J
    • 1.44 J

  14. If the circuit resistance is doubled, what happens to the discharge time constant of a capacitor?

    • It quadruples
    • It stays constant
    • It halves
    • It doubles

  15. What is the y-intercept of a graph plotting natural log of voltage against time for a discharging capacitor?

    • -1 / CR
    • ln(V0)
    • V0
    • e^(V0)

  16. A capacitor discharges from 12 volts to 4.41 volts in 2.0 seconds. What is the time constant?

    • 0.5 s
    • 1.0 s
    • 4.0 s
    • 2.0 s

  17. Which electrical quantity does the letter C represent in the capacitor energy formula W = 0.5 C V^2?

    • Charge
    • Capacitance
    • Current
    • Coulombs

  18. What is the initial current drawn when a capacitor charged to voltage V0 begins discharging through resistance R?

    • R / V0
    • V0 / R
    • V0 / CR
    • V0 R

  19. What is the half-life time for the charge on a discharging capacitor in terms of CR?

    • CR / ln(2)
    • 2 CR
    • CR ln(2)
    • CR / 2

  20. Which equation gives the energy W stored in a capacitor in terms of charge Q and capacitance C?

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

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