Answer:
In most devices, including headphones, earphones, radios, televisions and computers, electrical energy is transformed to sound energy by an electrodynamic loudspeaker. A speaker consists of a coil of wire suspended in a magnetic field. Changes in the current in the wire cause motion of the coil--the same principle of conversion of electrical to mechanical energy first demonstrated by Michael Faraday in 1821. The electrodynamic loudspeaker is actually a specialized form of electric motor. Like other electric motors, an electrodynamic loudspeaker can be also used in reverse--as a generator--to transform sound energy into electrical energy.