Also see voltage , resistance , and Ohm's Law . Current is a flow of electrical charge carriers, usually electrons or electron-deficient atoms. Electrons, the most common charge carriers, are negatively charged. They flow from relatively negative points to relatively positive points.
Electric current can be either direct or alternating.
The number of complete AC cycles per second is the frequency , which is measured in hertz . An example of pure DC is the current produced by an electrochemical cell. Current per unit cross-sectional area is known as current density . It is expressed in amperes per square meter, amperes per square centimeter, or amperes per square millimeter. Current density can also be expressed in amperes per circular mil.