Alternating current (AC) - Electric current that repeatedly reverses direction, twice each cycle. Usually at 60 cycles per second, or hertz (Hz), in North America, or 50 hertz elsewhere.
Ampere - SI unit of electric current, a flow of one coulomb of charge per second is one ampere (symbol A).
Diode - An electronic device that restricts current to flow in a single direction in an electric circuit,
Direct current (DC) - Electric current whose flow of charge is always in one direction.
Electric current - The flow of electric charge; measured in amperes (C/s).
Electric power - The rate at which electrical energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electrical energy).
Electric resistance - The resistance of a material to the flow of electric current through it; measured in ohms (symbol Ω).
Ohm (OM) - The SI unit of electric resistance. One ohm (symbol Ω) is the resistance of a device that draws a current of one ampere when a voltage of one volt is impressed across it.
Ohm's law - The statement that the current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit.
Potential difference - The difference in electric potential (voltage) between two points. Free charge flows when there is a difference, and will continue until both points reach a common potential.
Voltage source - A device, such as a dry cell or generator, that provides a potential difference.