The telephone or phone (Greek: tele = far away and phone = voice) is a telecommunication device which is used to transmit and receive sound (most commonly voice and speech) across distance. Electromagnets inside a telephone handset allow the caller to hear another person speaking. The mouthpiece contains a diaphragm that is vibrated by sound waves from a voice. These vibrations are converted into a varying electric current and sent down the telephone line. The signals can be heard because the receiver in the handset contains another diaphragm and an electromagnet. The variations in the current traveling down the telephone line vary the magnetic field that the electromagnet produces, making the diaphragm vibrate and reproduce the sound waves.
