Current, Charge and Potential Difference — AQA GCSE Physics

Electric current is a flow of charge, and potential difference provides the energy to drive it.

Charge and current

Electric current is the rate of flow of electric charge around a circuit. Charge is measured in coulombs (C) and current in amperes (A).

$$Q = I \times t$$

Q = charge (C), I = current (A), t = time (s).

So a current of 1 ampere is a flow of 1 coulomb of charge per second.

Potential difference

Potential difference (p.d.), or voltage, is the energy transferred per unit charge as charge moves between two points. It is measured in volts (V).

$$E = Q \times V$$

E = energy transferred (J), Q = charge (C), V = potential difference (V).

So 1 volt means 1 joule of energy is transferred per coulomb of charge.

Putting it together

The current depends on the potential difference and the resistance of the circuit. A bigger p.d. pushes a bigger current (for a fixed resistance).

Worked example

A current of 2 A flows for 30 s: Q = 2 × 30 = 60 C.

Exam tips

Current = rate of flow of charge; learn Q = It.
Potential difference = energy per unit charge; learn E = QV.
1 A = 1 C/s; 1 V = 1 J/C.
Watch units: time in seconds, charge in coulombs.

Current, charge and potential difference