Aerial (Antenna) A device to receive or transmit radio signals. It is also known as an antenna.
This type of variable capacitor is designed to be set when a circuit is made and then left without further adjustment.
A capacitor stores electric charge. It can be used with a resistor in a timing circuit, for smoothing a supply (it provides a reservoir of charge) and can be used as a filter (blocking DC signals but passing AC signals). Unpolarised capacitors usually have small values, less than 1µF.
Microphone A transducer which converts sound to electrical energy.