Capacitor charge and dischargeAQA A-Level Physics: Flashcards

What these 14 flashcards ask

What is the time constant of an RC circuit?
What does the time constant mean for a discharging capacitor?
State the equation for the charge on a discharging capacitor.
State the equation for current during discharge.
State the equation for the charge on a charging capacitor.
What happens to the current as a capacitor charges?
State the formula for the half-life of a capacitor discharge.
What does the gradient of a Q–t graph represent?
What does the area under an I–t graph represent?
What happens to the discharge time if R is doubled?
In RP9, what graph is plotted to find the time constant?
What are the gradient and intercept of the ln V against t graph?
Why should the voltmeter in RP9 have a high resistance?
After how many half-lives has the charge fallen to one eighth?

Exam questions on Capacitor charge and discharge

A 1000 µF capacitor is charged to 6.0 V and then discharged through a 22 kΩ resistor.
The 22 kΩ resistor is replaced by a 44 kΩ resistor. State and explain the effect on the initial discharge current and on the time taken for the capacitor to discharge.2 marks
A 470 µF capacitor charged to 9.0 V is discharged through a 10 kΩ resistor.
Calculate the discharge current at the start and 4.7 s later.2 marks
A 1500 µF capacitor, initially uncharged, is connected in series with a 3.3 kΩ resistor to a 12 V supply of negligible internal resistance, so that it charges through the resistor.
Calculate the p.d. across the capacitor 6.0 s after the circuit is connected.3 marks

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).