Chapter 21 Alternating Current Circuits and Electromagnetic Waves Quick Quizzes 1.(a), (c). The average power is proportional to the rms current which is non-zero even though the average current is zero. (a) is only valid for an open circuit, for which . (b) and (d) can never be true because R→∞av0i=for AC currents. 2.(b). Choices (a) and (c) are incorrect because the unaligned sine curves in Figure 21.9 mean the voltages are out of phase, and so we cannot simply add the maximum (or rms) voltages across the elements. (In other words, RLVV V VC∆≠∆+∆even though ∆.) vv v v∆=∆ +∆ +∆C3.(b). Note that this is a DC circuit. However, changing the amount of iron inside the solenoid changes the magnetic field strength in that region and results in a changing magnetic flux through the loops of the solenoid. This changing flux will generate a back
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