For electrical charge to flow through a closed circuit, the circuit must include a source of potential difference, such as a cell or a battery. Without one, the charge has nothing to push it round and there is no current.
Electric current is a flow of electrical charge. The size of the current is the rate of flow of charge, which means how much charge passes a point each second. Charge flow, current and time are linked by the equation: charge flow = current × time, or Q = I t. Charge flow Q is measured in coulombs (C), current I in amperes (A) and time t in seconds (s). Time must be in seconds, so 2 minutes must be changed to 120 s before it is used.
Worked example: a current of 3 A flows for 20 s, so the charge flow is 3 × 20 = 60 C. Rearranged, I = Q / t and t = Q / I. A current of 2 A for 50 s moves 2 × 50 = 100 C of charge.
In a single closed loop the current has the same value at any point. An ammeter placed anywhere in the loop gives the same reading, because charge is not used up as it goes round.