Energy of a Capacitor

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`E_C = 1/(2* C ) q ^2`

Enter a value for all fields

The Energy in a Capacitor calculator computes the energy based on the capacitance and charge.

INSTRUCTIONS: Choose units and enter the following:

(C) Capacitance
(q) Charge

Energy in a Capacitor (E_C): The energy is returned in Joules. However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The Capacitor's Energy is found using the following formula:

`E_C = 1/(2C)q^2`

where:

E_C = Capacitor's Energy
C = Capacitance
q = charge

Capacitors

A capacitor's energy exists in its surrounding electric fields. It is proportional to the square of the field strength, which is proportional to the charges on the plates. If we assume the plates carry charges that are the same in magnitude, +q and -q, then the energy stored in the capacitor must be proportional to q ². For historical reasons, we write the constant of proportionality as `1"/"2C`,

`E_C=1/(2C)q^2`.

The constant `C` is a geometrical property of the capacitor, called its capacitance.

Based on this definition, the units of capacitance must be coulombs squared per joule, and this combination is more conveniently abbreviated as the farad, `1 F=1 C^2"/"J`. “Condenser” is a less formal term for a capacitor. Note that the labels printed on capacitors often use MF to mean μF, even though MF should really be the symbol for megafarads, not microfarads. Confusion doesn't result from this nonstandard notation, since picofarad and microfarad values are the most common, and it wasn't until the 1990's that even millifarad and farad values became available in practical physical sizes. Figure a shows the symbol used in schematics to represent a capacitor.

References

25.1 Capacitance and inductance by Benjamin Crowell, Light and Matter licensed under the Creative Commons Attribution-ShareAlike license.