Telegraph was the early form of telecommunication trough which messages or information’s were converted into electric pulses by a transmitter. The current of these pulses is received very far away passing through wires where these signals comprising electric pulses are converted into audible signals. Latest telecommunication devices are much better and more efficient. These will be studied in this chapter.
Telephone
Working principle of a telephone is similar to telegraph but direct conversation can be processed by it. A microphone is fitted in the telephone handset. It changes vibrations produced by conversation into electric signals (Fig.20.1) which are transmitted along a wire to the receiver at the other and of the line. Here an electromagnet and a vibrating diaphragm change the electric signals again into sound. Network of telephone provides a contact between two telephones. In modern network exchange. Contacts are made through optical fiber system, microwave transmission or via satellites.
Cellular mobile phone
Radio technology is applied in a mobile phone. It is a type of a radio having two way communications. A mobile phone carries a radio transmitter and a receiver inside it. Sends and receives the messages in the form of radio waves. Our sound waves are converted into radio waves and then reach a nearby station which is linked with the telephone network. The area of each station works as a cell. When a call reaches from one cell to the other, the radio signals emitted by telephone get connected with the nest station by an automatic system. Mobile receiver again changes the radio signals into sound.
Another latest form of the telephone is the photo- phone or video-phone. Contrary to a common telephone, speakers can see the pictures of each other. It is the height of electronic communication that the distant speakers feel acquainted with the physical existence of each other.
Interesting information
1. The speed of sound in air is just 1246 km per hour and it cannot go far away from its source. Therefore, it is converted into electromagnetic wave so that they can be sent to far off areas with the speed of light.
2. Telegraph: the first contact of telecommunication.
Do you know?
1. Marconi has the distinction that he transmitted the first radio signal in the air.
2. Radio waves are electromagnetic waves.
http://www.youtube.com/watch?v=pcru4K8wsxQ