clredwolf posted:

AC/Alternating Current - Useful circuits often have voltages and currents that change dramatically over time. The changing currents and voltages are often refered to as 'AC'. This varying voltage can follow a sine wave pattern, square wave, or various other mathematically-defined waveforms. AC even describes 'random' signals such as sounds and digital information! Basically, if the voltage/current changes, it's AC.

NOTE: There's often a good overlap between AC and DC in circuits of any complexity. Transistor radios, for instance, have DC characteristics but obviously the circuit must be AC in nature. Therefore, it's imperative to know the ins and outs of both DC and AC. Thankfully, that's not quite as hard as it sounds most of the time.