Chapter Capacitance

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • 11CHAPTERCapacitanceELECTRICAL COMPONENTS CAN OPPOSE AC IN THREE DIFFERENT WAYS, TWO OFwhich you’ve learned about already.Resistance slows down the rate of transfer of charge carriers (usually electrons) by“brute force.” In this process, some of the energy is invariably converted from electricalform to heat. Resistance is said to consume power for this reason. Resistance is pre-sent in dc as well as in ac circuits, and works the same way for either direct or alternat-ing current.Inductance impedes the flow of ac charge carriers by temporarily storing the en-ergy as a magnetic field. But this energy is given back later.Capacitance, about which you’ll learn in this chapter, impedes the flow of ac chargecarriers by temporarily storing the energy as an electric field. This energy is given backlater, just as it is in an inductance. Capacitance is not generally important in pure-dc cir-cuits. It can have significance in circuits where dc is pulsating, and not steady.Capacitance, like inductance, can appear when it is not wanted or intended. As withinductance, this effect tends to become more evident as the ac frequency increases.The property of capacitanceImagine two very large, flat sheets of metal such as copper or aluminum, that are ex-cellent electrical conductors. Suppose they are each the size of the state of Nebraska,and are placed one over the other, separated by just a foot of space. What will happen ifthese two sheets of metal are connected to the terminals of a battery, as shown in Fig. 11-1?The two plates will become charged electrically, one positively and the other nega-tively. You might think that this would take a little while, because the sheets are so big.This is an accurate supposition.If the plates were small, they would both become charged almost instantly, attaininga relative voltage equal to the voltage of the battery. But because the plates are gigantic,199Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.