17. Conductors, Semiconductors and Insulators. 1430

Electronics has given us radar, automation, space vehicles, radio telescopes and a host of other inventions that have transformed our lives.

Electronics means putting electrons to work. An electron is one of the particles in an atom and travels at incredible speed round the nucleus. The electron has a negative charge, the nucleus has a positive one.

In cathode ray tubes, an electron beam is deflected by electric or magnetic fields, and passes over the face of the tube. These tubes are employed in TV receivers, oscilloscopes and other equipment.

Materials can be classed in three groups according to their electrical properties: conductors, semiconductors and insulators.

We use conductors to take current to the point where it is wanted. A conductor readily allows the free exchange of orbital electrons. Silver and copper are good conductors, for they allow current to flow freely.

We may need to direct current along a chosen path, and prevent its going elsewhere. Insulators help to do this. An insulator is a material which does not readily allow the passage of an electric current. A perfect insulator allows no exchange of electrons.

Glass, rubber and mica are good insulators, but there are many other substances. Rubber, cotton, silk or other insulating material on wires prevent the wires of touching each other or nearby metal parts where current is not wanted. What is the best kind of insulator depends on the work it must do.

18. Telecommunications: what is it and how does it work.

Part 1. 1257

Telecommunications embraces all devices and systems that transmit electronic signals across long distances. Telecommunications allows people around the world to contact one another, to access information instantly, and to communicate from remote areas.

Telecommunications usually involves a sender of information and one or more recipients linked by some form of telecom link.

The signals can then be transmitted by means of media such as telephone wires or radio waves. Telecom enables people to send and receive messages across towns, between countries, and to and from outer space. It also provides the key medium for news, data, information and entertainment.

Telecommunications messages can be sent in a variety of ways and by a wide range of devices. Messages can be sent from one sender to a single receiver (point-to-point) or from one sender to many receivers (point-to-multipoint).

Personal communications, such as a telephone conversation between two people involves point-to-point transmission. Point-to-multipoint telecommunications, often called broadcasts, provide the basis for commercial radio and television programming.

The messages to be transmitted are converted into electronic signals

and then decoded back into an understandable message.