Chapter Inductance

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

  • 10CHAPTERInductanceTHIS CHAPTER DELVES INTO DEVICES THAT OPPOSE THE FLOW OF AC BY temporarily storing some of the electrical energy as a magnetic field. Such devices arecalled inductors. The action of these components is known as inductance.Inductors often, but not always, consist of wire coils. Sometimes a length of wire, ora pair of wires, is used as an inductor. Some active electronic devices display induc-tance, even when you don’t think of the circuit in those terms.Inductance can appear where it isn’t wanted. Noncoil inductance becomes increas-ingly common as the frequency of an altemating current increases. At very-high, ul-tra-high, and microwave radio frequencies, this phenomenon becomes a majorconsideration in the design of communications equipment.The property of inductanceSuppose you have a wire a million miles long. What will happen if you make this wireinto a huge loop, and connect its ends to the terminals of a battery (Fig. 10-1)?You can surmise that a current will flow through the loop of wire. But this is onlypart of the picture.If the wire was short, the current would begin to flow immediately and it would at-tain a level limited by the resistance in the wire and in the battery. But because the wireis extremely long, it will take a while for the electrons from the negative terminal towork their way around the loop to the positive terminal.The effect of the current moves along the wire at a little less than the speed of light.In this case, it’s about 180,000 miles per second, perhaps 97 percent of the speed of lightin free space. It will take a little time for the current to build up to its maximum level.The first electrons won’t start to enter the positive terminal until more than five secondshave passed.The magnetic field produced by the loop will be small at first, because current is183Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.