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The Incandescent Circuit

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-426

2025-12-15

690

Incandescent lamps are coupled in parallel across the mains, or wires leading from the dynamo. Figure 1 illustrates a simple incandescent circuit. The dynamo D is first run until its voltage is 110 volts, and then any lamp or group of lamps in the circuit can be turned on. The hot resistance of a 110-volt, 16-candle-power lamp is about 220 ohms; consequently each lamp requires a current of half an ampere.

The parallel resistance of 2, 3, or n lamps being on 1/2 ,1/3, 1/n th part of the resistance of a single lamp, the same dynamo that will light one lamp will light a number. If it were possible to build a dynamo without any internal resistance, the number of lamps that could be lighted would be very large. As this cannot be done, the number is limited. Several groups of wires are usually run from one dynamo. A group can be run from the mains at any point by coupling submains to them, that is, by attaching to each wire a branch wire large enough to carry the current for its group (Fig. 2). It is customary to put a fuse (Fig. 3) between each branch circuit and the main.

FIG. 2.- Branch Circuits Each arch in the line where one conductor crosses another indicates that the two do not touch, or that they are insulated from each other.