Conductors and insulators

All substances have some ability of conducting the elec­tric current, however, they differ greatly in the ease with which the current can pass through them. Metals, for example, conduct electricity with ease while rubber does not ^llow it to flow freely. Thus, we have conductors and insulators.

What do the terms "conductors" and "insulators" mean? Substances through which electricity is easily transmitted are called conductors. Any material that strongly resists the electric current flow is known as an insulator.

Let us first turn our attention to conductance, that is the conductor's ability of'passing electric charges. The 4 factors conductance depends on are. the size of the wire used, =. its length and temperature as well as the kind of material to be employed. *

It is not difficult to understand that a large water pipe can pass more water than a small one. In the scum manner, a. large conductor will carry the current more readily than a thinner one. Fig. 7 illustrates this fact better than words alone!

It is quite understandable, too, that to flow through a short conductor is certainly easier for the current than through a long one in spite of their being made of similar ma­terial. Hence, the longer the wire, the greater is its opposi­tion, that is, resistance, to the passage of current.

As mentioned above, there is a great difference in the conducting ability of various substances. For example, almost all metals are good electric current conductors. Nevertheless, copper carries the current more freely than iron; and silver, in its turn, is a better conductor than copper.

Generally speaking, copper is the most widely used con­ductor. That is why the electrically operated devices in your home are connected to the wall socket by copper wires. In­deed, if you are reading this book by an electric lamp light and somebody pulls the metal wire out of the socket, the light will go out at once. The electricity has not been turned off but it has no path to travel from the socket to your electric lamp. The flowing electrons cannot travel'through space and get into an electrically operated device when the circuit is broken. If we use a piece of string instead of a metal wire, we shall also find that the current stops flowing.

A material like string which resists the flow of the elec­tric current is called an insulator.

There are many kinds of insulations used to cover the wires. The kind used expends upon the purposes the wire or cord is meant for. The insulating materials we generally use

^large

^{Fig. 7. Comparing water flow and current flow.}

to cover the wires are rubber, asbestos, glass, plastics and others.

Rubber covered with cotton, or rubber alone is the insu­lating material usually used to cover desk lamp cords and radio cords.

Glass is (he insulator to be often seen on the poles that carry the telephone wires in city streets. One of the most important insulators <rf all, however, is air. That is why . power transmission line wires are- bare wifes depending, on air to keep the current from leaking off.

Conducting materials are by no means the only, materials to play an important part Ш electrical engineering. Then£ must certainly be a conductor, that ife a path, akmg which., electricity is to travel and there must be insulators keeping it from leaking off the conductor.