Electricity: The Wonder-Worker

New Zealand Herald, Volume LXIX, Issue 21296, 24 September 1932, Page 4 (Supplement)

Electricity: The Wonder-Worker

By A.M.1.M.&

First of all then, an electric current must have a closed path, or circuit in which to flow. Each of the electric lamps in a house has its own separate circuit Avhich forms a branch of tho main circuit. Similarly, the radiator, iron, toaster, etc., each form part of a separate circuit. Thus it becomes a very simple matter to control each lamp, or appliance by a switch, which " makes " or * breaks the circuit. In large buildings a number of lamps are generally connected on one circuit, and are thus controlled by a single switch.

Now, a most, important feature of an electric circuit is that the nature of the conducting path makes an enormous difference in the behaviour Of the current. Copper wire is used as a conductor bocause it offers very little resistance to the flow of current; of all metals, copper is the best conductor, with the exception of silver, which, of course, is too expensive for general use. The size and length of the wire are important factors, also, in the resistance of the circuit. The smaller the wire and tho greater its length the higher its resistance will be. Resistance may bo considered as electrical fiction, reducing the quantity of current flowing. You will think, then, that resistance is certainly a nuisance which should be got rid of as far as possible. Yet it is this property which enables us to utilise electricity for producing heat. The flexible cord connected to the glowing radiator, for instance, provides an easy path for the current; we can handle the cord without detecting even the slightest warmth in it. But at the " element, that closely coiled spiral of fine wire, what a difference! Here the current meets a path of very high resistance, and has to push hard to

get through. It does not take the opposition coolly, either, but makes this difficult portion of its circuit red hot in getting past! The current is weakened to a certain extent by the power,- ifc expends in passing through the element; what happens is that part of tho electric energy is transformed into heat, which is another form of energy. Tho high resistance of the element in the radiator, toaster, iron, etc., is obtained by making tho wire very thin and long (tho idea of tho coils is to crowd a great length into a small space) and composed of an alloy of two metals, nickel and chromium. This alloy is used because it has certain special properties which aro needed in a heating element. It has a high electrical resistance and a high melting point, and can bo kept red-hot without, burning away, also it retains its strength at high temperatures, and thus is not easily broken. An iron wire for instance, would have to be extremely thin to have enough resistance to generate the necessary heat, and it would quickly oxidise or burn away, leaving nothing but rust.

It is an interesting fact that metals can actually be burned up if they are made hot enough, the process of burning or combustion being just the same aa in the case of wood or coal, that is, the oxygen in the atmopshere combines with the substance and oxidises it. It was not until recent years, and after very many experiments, that alloys suitable ior electrical heating elements were 'produced. In this talk I have dealt very briefly with one of those great discoveries upon which the present development in electrical engineering is founded, and have tried to show you how much we owe to the genius of that pioneer scientist, Michael Faraday. I think you will see that the principle upon which electric generators work is really quite simple, even though the construction of the machines themselves is a very intricate subject. (Concluded)