ELECTRIC CURRENT

Electric current is the flow of electric charge in the form of free electrons. Current is measured by the number of free electrons passing a particular point within a circuit per second. Therefore the flow of charge per unit second defines the amount of electric current. When the charge moves at the rate of 6.25 x 1018 electrons flowing past a given point per second, the value of the current is one ampere. This is the same as saying one coulomb of charge per second. The SI (International System of Units) unit of current is the ampere with letter symbol A.

Electric current has a direction associated with it. Conventional current flow is in the direction of positive charge movement from positive to negative. Electron flow is in the opposite direction from negative to positive. The arrow in a circuit specifies the direction of positive current flow. In solid metals only negatively charged free electrons move to produce a current flow, the positive protons can not move. But in a liquid or a gas, both the positive protons and negative electrons move to produce a current flow. Since electric circuits consist almost entirely of solid metal conductors such as copper wire, only negatively charged electrons produce a current flow. Current is also a measure of how intense or concentrated the electron flow is.