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Capacitor charge and dischargeEdexcel A-Level Physics: Flashcards

What these 14 flashcards ask

  • Write the equation for the charge on a discharging capacitor.
  • Write the equation for the current when a capacitor discharges.
  • Write the equation for the p.d. across a discharging capacitor.
  • Define the time constant.
  • What percentage of the initial value remains after one time constant?
  • What is the unit of RC?
  • Write the log form of V = V₀e^(−t/RC).
  • What does the gradient of a ln V against t graph give?
  • What does the intercept of a ln V against t graph give?
  • Describe how the current changes as a capacitor charges through a resistor.
  • Describe how the p.d. across the capacitor changes as it charges.
  • What is the time for V to halve on discharge?
  • Why must the voltmeter in the core practical have a very high resistance?
  • What effect does doubling R have on the discharge?

Exam questions on Capacitor charge and discharge

  1. A 2200 μF capacitor is charged to 9.0 V and then discharged through a 47 kΩ resistor.
    Calculate the time constant and the potential difference across the capacitor one time constant after discharge begins.2 marks
  2. A 470 μF capacitor is charged to 12 V and then discharged through a 10 kΩ resistor. The discharge starts at time t = 0.
    Calculate the current in the resistor 6.0 s after the discharge begins.2 marks
  3. A 1000 μF capacitor is charged to 6.0 V and is then discharged through a 22 kΩ resistor.
    Calculate how long it takes for the potential difference across the capacitor to fall to 2.0 V.3 marks
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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).