Capacitance
Capacitance measures how much charge a component can store per volt across it, and a charged capacitor holds energy in the electric field between its plates.
Practise this conceptA capacitor is built from two conductive plates separated by a small gap, and capacitance measures how much charge it can store on those plates per volt applied across them. A high-capacitance capacitor stores a lot of charge for a given voltage; a low-capacitance one stores comparatively little.
Once a capacitor in a simple DC circuit is fully charged, current stops flowing in that branch — not because the capacitor is somehow "used up," but because the buildup of charge on its plates opposes any further charge from arriving, until charging and opposing forces balance out exactly.
Capacitance is a property of the capacitor's physical construction — plate area, the gap between the plates, and what fills that gap — not of the voltage currently applied to it. Raise the voltage across a capacitor and you store more charge on it, but the capacitance itself, the ratio of the two, stays the same.
Key ideas
Requires: Voltage and resistance
Formulas
| Symbol | Name | Unit |
|---|---|---|
| electric charge | C (coulomb) | |
| capacitance | F (farad) | |
| voltage | V (volt) |
Common misconceptions
- A fully charged capacitor allows current to flow through it continuously, like a resistor.
- Increasing the voltage across a capacitor increases its capacitance.
- A capacitor stores current, not charge.