Radio Broadcast - 1924, January - 84 Pages, 8.2 ... - VacuumTubeEra

Various Circuits and What They MeanPART IIWhat Inductance Is and How It's UsedBy ZEH BOUCKis a thing encountereda circuit to induce a current by electromagnetic inductionwhen the 1invariably in radio circuits, and so oftenoriginal supplied current varies.referred to, that a genuine comprehension For the simplicity of the illustration, weof circuits isimpossible with no idea of haveINDUCTANCE"spoken of two circuits, one close to thewhat inductance is.other, the original or primaryTo current flowingdefine it clearly we must go back to our in one wire, and the secondary or induced currentflowing (always in the opposite direction)high-school physics, or even to those first electricalbooks we read in the days when our in the adjacent conductor. But supposing weelectrical research was concerned mainly with make a coil of the original conductor (a piece ofan electric doorbell, a wet cell, and a horse-shoemagnet. Those books told, of a mysterioussomething called "induction," concerning and we will have an induced current in thewhich the only thing most of us were able to same circuit. It isapparent that the numbergrasp was the fact that if one circuit or wire was of turns in the coil, their closeness together, etc.,near another circuit or wire, and the currentwas turned on or off in the first circuit, a currentwould be "induced," i.e., created, and mostly to deal may be defined as the abilitymade ofto flow in the second circuit. And that a circuit, in which is is pretty nearly all we need to know generally included a coilconcerning of wire (which furnishes almost all of the inductance)to generate a secondary current (ininduction in order to comprehend inductance.Here are several things about inductance, itself or in a near by circuit) when the originalhowever, which young fellows, digging into current varies. So much for "inductance."school text-books, are likely to be unable toassimilate: WheneverWHATa current flows IS AN INDUCTANCE?througha conductor (most often a wire), a "magnetic INDUCTANCEfield" the same sort of thing that attracts AvI is something possessingthe quality of inductance. The name isnails to a horse-shoe magnet springs up about most commonly appliedit. When to a coil of wire, becausea coil isthe current is turned off, the fielddrops. If the current becomes weaker, orstronger, the field does likewise. So we may closely associated with smoke, that a cigarettesay that with any change of current, the magneticfield caused by this current, "moves." enger, generally payingis often referred to as "a smoke" or a pass-Now a fare in a public conveyance,who is often simply designated as " aif a circuit isfare."Hence any coil of wire may correctly be calledan inductance.FAMILIAR FORMS OF INDUCTANCESor secondary, alternating current is always flowingin a direction opposite (at the instant of THE circuit in Fig. i is the diagram of whatin-is becoming an exceedingly popular receiver,the one-tube reflex. The photograph in Fig. 2Just why these things are so,inductance can be measured, and its unit is the "henry,"we have left to the world's great scientists to named after Joseph Henry, one of America's pioneers in thefind out.field of electromagnetism. A circuit has an inductanceof oneAt any rate, this evidence of induction is exactlywhat inductance a second induces an E. M. F. (electromotive force)henry when a current changing at the rate of oneampereis, namely, the ability of of one volt.crossed by a moving magneticfield, a current is induced in the circuit.This sort of induction isvery pronounced inthe case of alternating currents, because, assuch currents are always changing, the magneticfield isdoing likewise and this induced,duction} to the direction of the primary currentwhich induces it.copper wire, let us say). Then the magneticfield about one turn will cut the adjacent turns,will directly determine the inductance of the coil.Thus the inductance with which we havepredominantly characterized byinductance. It is like a cigarette, which is so