ELECTRIC CURRENT Is made up of moving electron charge. A light will come on immediately when the pathway is complete because the wires are already full of electrons and every electron that leaves the negative terminal of the battery pushes the one ahead of it. ELECTRIC POTENTIAL (VOLTAGE) The electric potential or voltage is the electrical energy that an electron possesses. As the electrons move through the circuit, they release their electrical energy to the electrical load(s) in the circuit. Potential difference (or voltage drop) refers to the loss of electric potential as an electron moves through a circuit. It is measured in volts. In a dry cell, a chemical reaction occurs, and the stored energy released by the reaction exerts a force on the electric charges and pushes a certain number of them on to the terminals of the dry cell. An excess of electrons accumulates on the negative terminal, thus giving it a negative charge, and a matching number of positive charges remain on the positive terminal. Electrons can be released with their electric potential energy in a circuit only when the switch is closed and electrons can flow completely around the circuit. MEASURING CURRENT Electric current refers to the amount of charge that passes a point in a conducting wire every second. Current ( I ) Charge moving past a point (Q ) Time (t ) Where: Q = charge, measured in coulombs (C) I = current, measured in amperes (A) t = time, measured in seconds (s) NOTE: One coulomb of charge (1 C) is equal to the amount of charge on 6.25×1018 electrons. An ammeter is an instrument that is used to measure electric current. MEASURING POTENTIAL DIFFERENCE Potential difference (V ) Energy ( E ) Charge (Q ) Where: E = energy, measured in Joules (J) V = potential difference, measured in volts (V) Q = charge, measured in coulombs (C) A voltmeter is an instrument that is used to measure potential difference between two points in a circuit.