Current

1. Current is the flow of charge and is preserved in a circuit
2. The current at a junction rule states that any junction in a circuit, the sum of the currents flowing into it is equal to the sum of the currents flowing out of it

Voltage

1. Voltage is the electric potential energy per unit charge between two points, and is used up in a circuit
2. The voltage at a point is indicated by calculating the potential difference relative to a 0 V reference using the voltage drops of the components in the circuit
3. Analogue signals continuously vary and digital signals are two-state

Resistance

1. Resistance is the opposition to current flow and is measured in ohms Ω
2. The potential difference between two points is equal to the product of the current & resistance: V = IR

Power

1. Power is dissipated when current flows through resistance and is measured in Watts W
2. The power is equal to the product of the voltage & current: P = VI

Unit prefixes