Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.
A variable capacitor is used in a radio tuner.
Earphone A transducer which converts electrical energy to sound.
Preset variable resistor A preset is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than standard variable resistors so they are sometimes used in projects to reduce the cost.