Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.
Electricity is the flow of charge around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors.
Zener diode A zener diode can be used to maintain a fixed voltage.
A NOT gate can only have one input. The o on the output means not. The output of a NOT gate is the inverse (opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter.