Energy stored by a capacitor (A-level only) Flashcards – AQA A-level Physics (7408)

How is energy stored when a capacitor is charged?

Work is done to separate charge.

Why does adding further charge to a capacitor require increasing work?

As charge accumulates, the potential difference across the capacitor rises.

How are charge $Q$, capacitance $C$ and potential difference $V$ related for a capacitor?

$Q=CV$

How can stored energy be found from a graph of charge against potential difference for a constant-capacitance capacitor?

It is the area under the graph up to the final potential difference. This area is a triangle.

What are the three equivalent expressions for the energy $E$ stored in a capacitor, in terms of $C$, $V$ and the charge magnitude $Q$ on either plate?

$E=\frac{1}{2}QV=\frac{1}{2}CV^2=\frac{1}{2}\frac{Q^2}{C}$