Telephone
A telephone , or 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.The word telephone has been adapted into the vocabulary of many languages.It is derived from the Greek : τῆλε , tēle , far and φωνή, phōnē , voice , together meaning distant voice.
The essential elements of a telephone are a microphone ( transmitter ) to speak into and an earphone ( receiver ) which reproduces the voice of the distant person.In addition, most telephones contain a ringer which produces a sound to announce an incoming telephone call, and a dial used to enter a telephone number when initiating a call to another telephone.Until approximately the 1970s most telephones used a rotary dial , which was superseded by the modern Touch-Tone push-button dial, first introduced by AT&T in 1963.The receiver and transmitter are usually built into a handset which is held up to the ear and mouth during conversation.The dial may be located either on the handset, or on a base unit to which the handset is connected by a cord containing wires.The transmitter converts the sound waves to electrical signals which are sent through the telephone network to the receiving phone.The receiving telephone converts the signals into audible sound in the receiver, or sometimes a loudspeaker.Telephones are a duplex communications medium, meaning they allow the people on both ends to talk simultaneously.
A landline telephone is connected by a pair of wires to the telephone network , while a mobile phone , such as a cellular phone, is portable and communicates with the telephone network by radio transmissions.A cordless telephone has a portable handset which communicates by radio transmission with the handset base station which is connected by wire to the telephone network.
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| Telephone from Swedish Ericsson 1001 model, from 1939 |
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| 1896 Telephone from Sweden |
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