Fig. 253.—The three conductors are connected in parallel.
This rule may be understood better if we consider the conductance of the conductors in parallel. Since the conductance of a two ohm wire is just one-half that of a one-ohm wire, we say that the conductance of a body is inversely as the resistance, or that it is the reciprocal of the resistance. The conductance of the 4-, 6-, and 3-ohm coils will therefore be respectively 1/4, 1/6, and 1/3, and since the combined conductance is the sum of the several conductances, the total conductance is 18/24. Also since this is the reciprocal of the total resistance, the latter is 24/18 or 1-1/3 ohms.
When two or more conductors are connected in parallel each one is said to be a shunt of the others. Many circuits are connected in shunt or in parallel. Fig. 254 represents four lamps in parallel. Incandescent lamps in buildings are usually connected in parallel, while arc lamps are usually connected in series. Fig. 255 represents four lamps in series.
Important Topics
1. Conditions affecting current flow, (a) E.M.F., (b) resistance.
2. Ohm's law, three forms for formula.
3. Resistance of conductors: (a) in series, (b) in parallel; how computed, illustrations.
Fig. 255.—The four lamps are connected in series.
Fig. 254.—The four lamps are connected in parallel.