IP What is electric current? © Oxford University Press 2011 What is electric current?

IP What is electric current? © Oxford University Press 2011 An electric current is a flow of charge around a circuit. Negatively charged electrons flow from the negative terminal of a cell round the circuit to the positive terminal.

IP What is electric current? © Oxford University Press 2011 The charge carried by each electron is very small, so electric charge is measured in a much larger unit called the coulomb, with the symbol C. The size of the current is given by the amount of charge passing a point in a circuit each second. current (amperes, A) = If the current is called I, the charge Q and the time t, then I =

IP What is electric current? © Oxford University Press 2011 If a charge of 400 C passes a point in a circuit in 80 seconds, what is the current in the circuit? Using: I = I = 400 / 80 = 5 A

IP What is electric current? © Oxford University Press 2011  Scientists used to think that positive charge flowed from the positive terminal of a cell to the negative terminal. They called this conventional current.  Scientists now know that the negative electrons are the charges that flow in a circuit and they flow from the negative terminal of a cell to the positive terminal.  Be careful on circuit diagrams because the arrows still point in the direction of conventional current!