Physics TELEPHONE

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TELEPHONE

Telephone

A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart 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.

In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice.

The telephone was the first device in history that enabled people to talk directly with each other across large distances.

`text(Parts of a Telephone)`
A telephone is not just the thing that sits on your table at home. It's a complete system: the handset at your end, the cable that runs into the wall, a whole collection of communication apparatus (copper cables, fiber-optics, microwave towers, and satellites) that carries telephone signals across country, some switching apparatus that makes sure calls get to the right place, and a handset at the other end.

The main parts of a telephone are:

Microphone
Earphone/Loudspeaker
Keypad
Transducer

A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart 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.

In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice.

The telephone was the first device in history that enabled people to talk directly with each other across large distances.

`text(Parts of a Telephone)`
A telephone is not just the thing that sits on your table at home. It's a complete system: the handset at your end, the cable that runs into the wall, a whole collection of communication apparatus (copper cables, fiber-optics, microwave towers, and satellites) that carries telephone signals across country, some switching apparatus that makes sure calls get to the right place, and a handset at the other end.

The main parts of a telephone are:

Microphone
Earphone/Loudspeaker
Keypad
Transducer

Basic Principles

A traditional landline telephone system, also known as plain old telephone service (POTS), commonly carries both control and audio signals on the same twisted pair (C in diagram) of insulated wires, the telephone line.

The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial. The ringer, or beeper, light or other device (A7), alerts the user to incoming calls.

The hook-switch signals to the central office that the user has picked up the handset to either answer a call or initiate a call. A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call.

Until the 1960s dials used almost exclusively the rotary technology, which was replaced by dual-tone multi-frequency signaling (DTMF) with push-button telephones (A4).

A major expense of wire-line telephone service is the outside wire plant.

Telephones transmit both the incoming and outgoing speech signals on a single pair of wires.

A twisted pair line rejects electromagnetic interference (EMI) and cross-talk better than a single wire or an untwisted pair.

The strong outgoing speech signal from the microphone (transmitter) does not overpower the weaker incoming speaker (receiver) signal with side-tone because a hybrid coil (A3) and other components compensate the imbalance.

The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line length. Telephones have similar adjustments for inside line lengths (A8).

The line voltages are negative compared to earth, to reduce galvanic corrosion. Negative voltage attracts positive metal ions toward the wires.

A traditional landline telephone system, also known as plain old telephone service (POTS), commonly carries both control and audio signals on the same twisted pair (C in diagram) of insulated wires, the telephone line.

The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial. The ringer, or beeper, light or other device (A7), alerts the user to incoming calls.

The hook-switch signals to the central office that the user has picked up the handset to either answer a call or initiate a call. A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call.

Until the 1960s dials used almost exclusively the rotary technology, which was replaced by dual-tone multi-frequency signaling (DTMF) with push-button telephones (A4).

A major expense of wire-line telephone service is the outside wire plant.

Telephones transmit both the incoming and outgoing speech signals on a single pair of wires.

A twisted pair line rejects electromagnetic interference (EMI) and cross-talk better than a single wire or an untwisted pair.

The strong outgoing speech signal from the microphone (transmitter) does not overpower the weaker incoming speaker (receiver) signal with side-tone because a hybrid coil (A3) and other components compensate the imbalance.

The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line length. Telephones have similar adjustments for inside line lengths (A8).

The line voltages are negative compared to earth, to reduce galvanic corrosion. Negative voltage attracts positive metal ions toward the wires.

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