All courses › Electric Circuits › Capacitor

Capacitor

A capacitor stores energy in an electric field between two plates. The charge it stores is proportional to the voltage across it, and it prefers constant voltage – the current through it depends on how fast the voltage changes. In a DC circuit at steady state it behaves as an open circuit.

Q = CU

charge stored on a capacitor

i = C\dfrac{du}{dt}

current as a function of the rate of change of voltage

E = \tfrac12CU^2

energy stored in the electric field

Symbols

$Q$	charge	C
$C$	capacitance	F
$U$	voltage across the capacitor	V
$E$	stored energy	J

Example

$C=220$ µF charged to $U=15$ V:

$Q=CU=220\cdot10^{-6}\cdot15\approx3.3$ mC.

The voltage across a capacitor cannot jump instantaneously – only the current can.

Practise capacitors and inductors for free →

← Kirchhoff's Laws · Inductor →

Part of Electric Circuits: Capacitors and inductors.