Capacitance and energy storedEdexcel A-Level Physics: Flashcards

What these 12 flashcards ask

Define capacitance.
State the unit of capacitance.
Write 470 μF in farads.
What does the gradient of a Q against V graph give?
What does the area under a V against Q graph represent?
State three equations for energy stored in a capacitor.
Why is the energy stored ½QV and not QV?
What happens to the energy stored if V is doubled?
How much of the energy supplied by a battery is stored when a capacitor charges through a resistor?
When is W = Q²/2C the best equation to use?
How do you find the energy released when a capacitor discharges from V₁ to V₂?
What is the charge on a capacitor 'Q'?

Exam questions on Capacitance and energy stored

A 2200 μF capacitor is connected across a 9.0 V supply and allowed to charge fully.
Calculate the charge stored and the energy stored when the capacitor is fully charged.2 marks
The flash unit of a camera uses a capacitor of capacitance 120 μF, which is charged to a potential difference of 330 V before the flash is fired.
Calculate the energy stored in the capacitor at 330 V.2 marks
A memory-backup circuit uses a 0.47 F capacitor charged to 5.0 V. When the supply fails, the capacitor powers a data logger that needs a potential difference of at least 3.0 V across it to work. While it works the logger transfers energy at a constant 0.80 W.
Calculate the energy stored in the capacitor and the charge stored on it when it is fully charged.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).