Alternating Current

What makes a current alternating?

In an alternating current, abbreviated to a.c., the charge carriers move in one direction and then reverse, moving in the opposite direction. This reversal repeats while the alternating current is present.

Imagine observing one small region of a wire at successive times. At first, electrons move through that region one way. Later, their direction is reversed. They therefore move back and forth rather than continuing around the circuit in only one direction.

This back-and-forth movement can still transfer energy from an energy source to a device. The defining feature of a.c. is the changing direction of charge movement, not an absence of energy transfer.

Distinguishing a.c. from d.c.

With direct current, or d.c., charge moves in one direction only. With alternating current, charge movement repeatedly reverses. A current that merely switches on and off but always moves in the same direction is not alternating current.