FACTS ABOUT CONDENSORS

Radio Record, Volume I, Issue 40, 20 April 1928, Page 12

FACTS ABOUT CONDENSORS

A CONDENSER is described as being | of a certain capacity-i.e., .0005mid, ‘The farad is the measure of capacity. ‘Ihe property which a condenser has of holding a charge of electricity is called its capacity. An excellent example of this property.of the condenser is that of a spiral spring. If a metal weight is attached to the end of the spring, the spring will be extended to a certain iength until the weight of the metal is exactly equal to the force ex--erted by the spring in the opposite direction.

DIKLECTRIC STRAIN. yy the same way, if ore plate of a condenser be charged with a certain electrical force, the dielectric or intervening material between the two plates of the condeuser will be strained electrically until the condenser exerts an electrical pressure equal and opposite to the electrical force applied to it. he two plates of a condenser are conductors of electricity; and reccive the electric charge upon them. They are separated froin each other by nonconductive material called the dielectric, which may be composed of mica, glass, or of air. ‘here may be more than two plates to a condenser-and generally are-dependent on the capacity required, but between the plates there must be a dielectric. CAPACITY OF CONDENSERS, WE find that the capacity of a condenser depends upon the arca of the plates of which it is formed, and the material of which the dielectric is composed. But there are other things which affect the capacity of the condenser, We say that the capacity of a water tank is of so many gallons, meaning that it will hold so many gallons of water when completely full. Ve do not fill a condenser with ecectricity in the same way. We apply an electrical pressure to the plates of the condenser, causing a state of strain to be set up upon the dielectric between the plates. The thicker or higher the water tank the greater the amount of water it will hold, and the greater its capacity. But, in the case of a condenser, the thicker the dielectric, or the greater the distance between the two plates, the less will be the state of straiu upon the dielectric, and the fess the capacity, The thinness of an india rubber tube "will allow of its greater expansion when Ub. pressure of water is applied to it. The thinner the dielectric the greater will be the state of strain existing in it, and the gveater will be the capacity of the condenser. The capacity of the aerial cireu’t has its effect on the wave-length to which that circuit is tuned. You will remember that in my last article I talked of tuning and coupling, aud I said that to facilitate: the tuning cf the acvial and closed circuits a variable condenser could be added to the circuits. By varying the capacity of the conéenser in such a circuit {he tuning of that cirenit is controlled. If a condenser is inserted in the acrial circuit-shall we say between the aerial and the tuning-coil-we reduce the capacity of the circuit, and, therefore, the wave-length. ‘Ike aerial itself has a capacity which can be increased by increasing the number of wires forming the aerial, and if a condenser is inserted in series with the acrial the total capacity of the circuit is not thereby increased as might be supposed, but decreased, and an increase of capacity causes a decrease of wave-length of the aerial. | TUNING ‘THI, AERIAL. , ON the other hand, the aerial itself. has inductatice, and if an inductance is inserted in the circuit the total (Continned on-Page 13.)