Capacitance
Capacitors
- Capacitors store energy by means of an electric field.
- A capacitor is made out of two plates with an insulating material (a
dielectric) placed between the two plates.
- In order to store energy (create the electric field), charge needs to be
moved from one plate to the other leaving one plate negatively charged and the
other plate positively charged. Work must be done to move charge from
one plate to the other. In the circuit shown below a battery is used to
do the work. Charge will continue to be moved until the potential
difference between the plates is equal to the potential difference across the
battery.
- According to the Law of Conservation if work is done on the capacitor the
capacitor has gained energy. In other words the capacitor has stored
energy.
- The amount of charge, Q that is moved from one plate to the other
is proportional to the potential difference across the plates, V.
| Charge on one plate
µ |
Potential Difference
between the plates |
| Q µ |
V |
| Q = |
Capacitance · V |
| Q = |
C · V |
Capacitance is measured in Coulombs / Volt or Farads.
A 1 Farad capacitor can store 1 Coulomb of charge at 1 Volt.
What determines how good a capacitor is?
Good sites on Capacitors
How Stuff Works