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About 100 years ago, Alexander Graham Bell invented the telephone by accident with his assistant Mr. Watson. Over many years, the modern version of the telephone makes the one that Bell invented look like a piece of junk. Developments in tone dialing, call tracing, music on hold, and electronic ringers have greatly changed the telephone.

This marvelous invention allows us to communicate with the entire globe 24 hours a day just by punching in a simple telephone number. It is the most used piece of electronic apparatus in the world. It is probably one of the most easy to use electronics available too. All you have to do is pick up the receiver, listen for the tone, and then select a number using either tone or pulsing dial.

A telephone can be separated into two main categories: there is the tone (touch tone) or the older rotary dial (pulse) telephones. Then you can divide those into other categories such as business line (multi -- line) or home line (single line). You can also have many other types of phones: there are those that hang on the wall, on the desk, etc.

THE HANDSET

No matter what kind of telephone you own, there has to be some device that allows you to talk to and listen to. This device is called the handset. The handset is usually made out of plastic and inside it are two main components: the transmitter and the receiver.

THE TRANSMITTER

It is the job of the transmitter to turn the air pressure created by your sound waves to

electrical signals so they can be sent to the other telephone. The waves hit a thin skin called the diaphragm that is physically connected to a reservoir of carbon granules. When the pressure hits the diaphragm, it shakes up the carbon granules. Then the carbon expands and contracts, depending on what force is exerted. At two points on the outer shell of the reservoir of the carbon are two outlets of electricity from the talk battery. By applying voltage, a current is made and is passed along the lines to the waiting telephone. At the other end the current is transformed back to speech.

THE RECEIVER

The receiver turns an ever varying current back to speech. A permanently magnetized soft iron core is covered in many turns of very fine wire. Through the wire, the electrical current is applied. The currents attract and repel an iron diaphragm. By the vibrating actions the diaphragm does, a different pressure is created and these pressures are translated by ear into intelligible speech.

TELEPHONE NETWORKS

If you have ever opened up a phone (do not try this at home, you might screw it up) you will probably see a PC (printed circuit) board. The board contains the needed electronics for the phone to work properly. In older models of a working telephone, this board may look like an electronic box. This board is called the telephone network.

The telephone network's function is to provide all the necessary components and termination points (screw on or push on terminals). The components and the termination points connect and match the impedance of a handset (transmitter and receiver) to a two -- wire telephone circuit.

Every component in the telephone has to be connected to the PC board. Usually, the board is the most reliable component inside the phone. All the delicate components are securely sealed by a metal enclosure. The PC board is a very fragile object and can be 本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。