# Capacitance

- Capacitors are used to store charge.
- The capacitance of a capacitor is the value that tells you how good a capacitor is at storing charge

Capacitance = Charge stored on a capacitor / Voltage across the capacitor

- Capacitance (C) = Q / V
- Q = Coulombs (c)
- V = Volt
- Coulomb / Volt = Farad (F)

Capacitors store Electrical Potential Energy:

- PE
_{electric}= QV

But, E_{of a capacitor} = 1/2 QV

- Not all of the charges drop through the voltage V
- As charge decreases, the voltage across the capacitor decreases
- Only the first charge drops through voltage V

Here we have two plates with charge of -6, and +6; denoted with the plus and minus symbols.

- The electrons are going to move to the positive plate
- Now, on the first go, the positive plate has 6/6 = 100%

- On the third one, the positive plate only has 4/6 at the ‘time of departure’, which is 66%

- The fifth one has 2/6 = 33%, and so on:

**Thus, E = 1/2 QV**