Certified Radio-Trician's Course(REG. U. S. PAT. OFF.)
NATIONAL RADIO INSTITUTE
WASHINGTON, D. C.
RESITANCES IN SIMPLE CIRCUITS
Now that we have learned how to divide electrical and Radio circuits into groups of single circuits which can be traced (followed) through, we must learn how to calculate the values of the currents flowing in these circuits; knowing the voltages and the various electrical factors that oppose the flow of current, namely, resistance, inductance and capacity opposition. This text-book, however, will be devoted to the first of these--resistance. The e.m.f. in this circuit is produced
Fig. 1
by a dry cell and the load is a flash light bulb, such as used in electric Radio receivers to light up the tuning dial. An electric light bulb is nothing more than a resistance wire in a glass bulb out of which the air has been withdrawn---that is, a resistance wire in a vacuum.
Fig. 1(b) shows this simple circuit in diagram form, using the symbols for the apparatus. When a source of e.m.f. is connected to a resistance forming a complete circuit as shown in Figs. 1(a) and (b), a current will flow, its value being determined by the resistance of the circuit.
Ohm's Law, as you know, states that the current (I) is always equal to the e.m.f.) divided by the resistance (R). If the e.m.f. is measured in volts and the resistance in ohms, the
