Direct Current Circuit Analysis

Chapter Direct Current Circuit Analysis

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • 825CHAPTERDirect-current circuitanalysisIN THIS CHAPTER, YOU’LL LEARN MORE ABOUT DC CIRCUITS AND HOW THEYbehave. These principles apply to almost all circuits in utility ac applications, too.Sometimes it’s necessary to analyze networks that don’t have obvious practical use.But even a passive network of resistors can serve to set up the conditions for operationof a complex electrical device such as a radio amplifier or a digital calculator, by pro-viding specific voltages or currents.Current through series resistancesHave you ever used those tiny holiday lights that come in strings? If one bulb burns out,the whole set of bulbs goes dark; then you have to find out which bulb is bad, and re-place it to get the lights working again. Each bulb works with something like 10 V; thereare about a dozen bulbs in the string. You plug in the whole bunch and the 120-V utilitymains drive just the right amount of current through each bulb.In a series circuit, such as a string of light bulbs (Fig. 5-1), the current at any givenpoint is the same as the current at any other point. The ammeter, A, is shown in the linebetween two of the bulbs. If it were moved anywhere else along the current path, it wouldindicate the same current. This is true in any series dc circuit, no matter what the com-ponents actually are and regardless of whether or not they all have the same resistance.If the bulbs in Fig. 5-1 were of different resistances, some of them would consumemore power than others. In case one of the bulbs in Fig. 5-1 burns out, and its socket isthen shorted out instead of filled with a replacement bulb, the current through the wholechain will increase, because the overall resistance of the string would go down. Thiswould force each of the remaining bulbs to carry too much current. Another bulb wouldprobably burn out before long. If it, too, were replaced with a short circuit, the currentCopyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.