This device is used in broadcasting, recording, and sound-amplifying systems to convert sound into electrical energy. Its basic component is a flexible diaphragm that responds to the pressure or particle velocity of sound waves. In an electrostatic, or condenser, microphone, two parallel metal plates (electrodes) are given opposite electrical charges. One of the plates is attached to the diaphragm and moves in response to its vibrations, generating a varying voltage. An electorate microphone, the most widely used type, has a permanently charged dialectic (electorate) between the two electrodes. This device was invented in 1877.