Definition
Capacitance
(E4.1.1) E4.1 · Definition of Capacitance →Statement
Charge stored per volt applied. Always positive.
Symbols and units
| capacitance | F = C/V | |
| charge on either conductor | C | |
| voltage between them | V |
When it applies
Two conductors carrying equal and opposite charge.
Derivation
Put charge ±Q on the two conductors. The field between them is proportional to Q:
The voltage is the field integrated across the gap, so it is proportional to Q as well:
The ratio therefore does not depend on how much charge you put on — it is a property of the arrangement:
Watch out for
C never changes when you disconnect the battery. Q or ΔV may — and which one stays fixed is the decisive question in nearly every capacitor problem.
Connects to