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

flashcards

QuestionAnswer
Charge (Q)Unit is Coulomb (C), where 1C = 6.25\times10^{18} electrons
Current (I)Unit is Ampere (A), defined as rate of flow of charge
Potential difference (V)Unit is Volt (V), defined as work done per coulomb charge
Resistance (R)Unit is Ohm (\Omega), defined as opposition to current flow, ratio of p.d. to current
What is the symbol for charge?Q
What is the unit of current and its symbol?Ampere, A
What is the definition of potential difference?Work done per coulomb charge
What is the definition of resistance?Opposition to current flow, ratio of p.d. to current
How many electrons make up 1 Coulomb of charge?6.25\times10^{18} electrons