OCR Text |
Show Radio Club Notes Conducted by G. S. Morris Lesson 2, parts 1 and 2, indicated indicat-ed the action of inductance and capacity and the action of the two j in combinaion. A circuit comprising compris-ing inductance and capacity is known as an escillating circuit; the process of varying either of 1 the two is known as tuning that ' circuit; the final response of the circuit to another circuit, which may be either a radio transmiter or other source of A C, is called resonance. If the second circuit, 1 which we are not speaking of, is' in "tune", the circuit is then said to be in resonance, which condition condi-tion must always exist before an efficient transfer of energy will take place. Every circuit comprising inductance induc-tance and capacity has a resonance reson-ance point. When the units of inductance in-ductance and capacity are fixed the point of reasonance is fixed, when the units are variable, either both or one of either, the point of resonance is likewise variable. In addition to varying the point of resonance by variation of capacity, the variation of inductance may also take place either by use of taps on the coil or by use of a variometer, whidh has the same effect. A circuit comprising "pure" inductance, in-ductance, which means no capacity and no ohmic resistance will oscillate oscil-late of its own accord for an indefinite in-definite period. Experiments along this line are not new; in fact, at "absolute zero" fahrenheit, when the ohmic resistance is zero, a small ring of wire, which is inductance, in-ductance, will continue to oscillate for lengthy periods. So far we have dealt with properties pro-perties of inductance at radio frequencies. On low frequencies (adio frequencies) which would include house light frequencies of 2f, 50 or CO cycle A C current, we !find that the combination of in- ductance and ohmic resistance of ' the windings of a coil, is termed impedance, and, as it is a form of resistance is measured in "ohms," indicated in formulaes by the sign Reactance, which is the "self-inductance" "self-inductance" of a coil, is indicated by the sign "X". It is therefore possible by use of a rule, similar to ohms law, to obtain any one of the three units when two units are known. (Continued next week) |