For electrical charge to flow through a closed circuit the circuit must include a source of potential difference. • Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge. Charge flow, current and time are linked by the equation: charge flow = current × time, Q = I t (charge flow, Q, in coulombs, C; current, I, in amperes, A (amp is acceptable for ampere); time, t, in seconds, s) • A current has the same value at any point in a single closed loop. • Students should be able to recall and apply this equation.