Summary of the 4 main quantities

Summary of the 4 main quantities

There are four main quantities we need to think about when working with electrical circuits.

These are explained much more over the next few pages, but here is a summary:

QuantitySymbolUnitUnit SymbolDefinition
ChargeQCoulombC$1C = 6.25\times10^{18} electrons
CurrentIAmpereARate of flow of charge
Potential differenceVVoltVwork done per coulomb charge
ResistanceROhm\OmegaOpposition to current flow, ratio of p.d. to current