202CHAPTER 21 Answers to Even Numbered Conceptual Questions 2.At resonance, X. This means that the impedance LX=C)(22LCXX=+−ZRreduces to Z= R. 4.The purpose of the iron core is to increase the flux and to provide a pathway in which nearly all the flux through one coil is led through the other. 6.The fundamental source of an electromagnetic wave is a moving charge. For example, in a transmitting antenna of a radio station, charges are caused to move up and down at the frequency of the radio station. These moving charges set up electric and magnetic fields, the electromagnetic wave, in the space around the antenna. 8.Energy moves. No matter moves. You could say that electric and magnetic fields move, but it is nicer to say that the fields stay at that point and oscillate. The fields vary in time, like sports fans in the grandstand when the crowd does the wave. The fields constitute the medium for the wave, and energy moves.
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