Does a Condenser Condense?

Radio Record, Volume II, Issue 16, 2 November 1928, Page 5

Does a Condenser Condense?

A Non-technical Chat on Question often asked

HE condenser is known to most radio beginner's, or to those unacquainted with their sets as "the thing behind the dials." — It is known that. by altering the relation of one set of plates ( vanes) to another, stations operating on different wavyelengths can be brought in. Certainly that is a condenser but. its function cannot be limited there. It is one of the most important pieces of apparatus, or should it be said essentials, where electricity is at all made use of. A Condensing Condenser.

{t is not altogether clear just how the condenser earned its name, for so far as designating its function the name is very misleading. Probably it obtained the name from the fact that its electrical-storing capacity formed the first-known of its several valuable properties, for primarily the condenser is a storer. The condenser was invented about the middle of the 18th century when electricity was supposed to be an invisible and intangible fluid. Thus if may be supposed that the condenser received its name because, recognising its storing capacity the inventor colsidered that to store electricity it must first be condensed. ‘The earliest forms of condensers consisted of a vessel containing water "yinto which dipped a brass chain. An "electric charge was imparted to this crude condenser by placing the end of the chain in contact with a frictional electric machine. These, it will be remembered, were the days when static electricity only was known, and when electricity in any other form, e.g., that of a continuous or alternating current. was not conceived. Leydon Jar. (PHEN came the well-known Leydon jar consisting of a glass cylinder coated inside and out with tinfoil, a metallic chain, again making contact with the interior of the device. This was capable of storing up a considerable electric charge, as probably every schoolboy has found out to his disecownforture, for the charge can be raised to high voltage, but of little amperage. The charge is analagous to that held in the patches of ionised air referred to in a previous article.

Does an Accumulator Store ? T may be contended that an accumulator, such as used for the A battery. is a storer of electricity. Strictly speaking this is not the case. An acecumulator does not store electricity as such. What it really does is to convert electrical current into a form of reserve chemical energy which is reconverted into electrical energy when the accumulator is discharging. This is really an adaptation from Nature. All life receives energy froin the sun and food, changes its form into fat, sugar, starch, or oil, as the case may be, to reconvert it at a future time

when this supply is not available. This explains hunger, as well as the reasons for regular feeding and regular chareging of batteries. A Modern Condenser. T has been shown that the accumulator is not a true storer of electricity. The condenser, on the other hand, stores electricity as such. The simplest condenser comprises two metalic plates held close tagether, but not touching. They are separated by an insulator-air. Air is not the best insulator and so in practise miga, parafin wax, paper, and a host of other nonconductors are used in the making of the fixed condenser, or storer with a fixed capacity. Funetion of a Condenser. {t is now known that an electrical charge simply consists of an accumulation of electrons-those almost infinitisimally minute particles of matter which enter into the constitution of the atom, When these electrons are set in motion along a conductor we get the phenomenon associated with an electric current. In considering the stationary accumulation of these electrons let it be supposed that the condenser is charged so that there is an accumulation of electrons on, say, the upper plate or plates. Under these conditions the

electrons will rush away from the overcrowded plates, through the circuit (supposing the two plates to be connected by a suitable circuit, eg., an oscillatory cireuit such as in the ordinary receiving set) on to the lower plates. These plates rapidly become overcharged and the electrons rush back to the upper plates. This sequence of events will occur, provided outside circuit is suitable, with a ‘apidity of many thousands of times per second till the energy is frittered away by the resistence losses in the circuit. This surging backward and forward

of oryercrowding electrons gives rise to an oscillating current. and it is this property of the condenser which makes it of so much value for radio purposes. The Tuning. N the yariable condenser, through means of which the set is tuned, the areas of the opposing plates can be varied at will, and with this variation we have a complete contro] of the capacity or storing properties of the condenser. Thus it is obvious. that the rapidity with which the electrons rush from one set of plates to the other. This is tuning or governing the fre-

quencies of the oscillatory eurrent to which the condenser gives rise. By altering the relation of the moving to the fixed vanes, the circuit can be made to oscillate in harmony with that of the station desired. Frequencies are merely an expression of wavelength.