The phone is a telecommunications device that permits two or more users to conduct a conversation when they are not in the same vicinity of each other to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals suitable for transmission via cables or other transmission media over long distances, and replays such signals simultaneously in audible form to its user.
Telephones became rapidly indispensable to businesses, government, and households, and are today some of the most widely used small appliances.
commonly carries both control and audio signals on the same twisted pair (C) of insulated wires: the telephone line. The signaling equipment, consists of a bell, beeper, light or other device (A7) to alert the user to incoming calls, and number buttons (A4) to enter a telephone number for outgoing calls.. The strong outgoing voice signal from the microphone does not overpower the weaker incoming speaker signal with a sidetone because a hybrid coil (A3) subtracts the microphone's signal from the signal sent to the local speaker. The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line's length. Telephones have similar adjustments for inside line lengths (A8).
