# Chap 29 SM - Chapter 29 Alternating-Current Circuits...

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747 Chapter 29 Alternating-Current Circuits Conceptual Problems 1 A coil in an ac generator rotates at 60 Hz. How much time elapses between successive peak emf values of the coil? Determine the Concept Successive peaks are one-half period apart. Hence the elapsed time between the peaks is () ms .33 8 s 60 2 1 2 1 2 1 1 = = = f T . 2 If the rms voltage in an ac circuit is doubled, the peak voltage is ( a ) doubled, ( b ) halved, ( c ) increased by a factor of 2 , ( d ) not changed. Picture the Problem We can use the relationship between V and V peak to decide the effect of doubling the rms voltage on the peak voltage. Express the initial rms voltage in terms of the peak voltage: 2 peak rms V V = Express the doubled rms voltage in terms of the new peak voltage peak V' : 2 2 peak rms V' V = Divide the second of these equations by the first and simplify to obtain: 2 2 2 peak peak rms rms V V' V V = peak peak 2 V V' = Solving for peak V' yields: peak peak 2 V V' = ) ( a is correct. 3 [SSM] If the frequency in the circuit shown in Figure 29-27 is doubled, the inductance of the inductor will ( a ) double, ( b ) not change, ( c ) halve, ( d ) quadruple. Determine the Concept The inductance of an inductor is determined by the details of its construction and is independent of the frequency of the circuit. The inductive reactance, on the other hand, is frequency dependent. ) ( b is correct. 4 If the frequency in the circuit shown in Figure 29-27 is doubled, the inductive reactance of the inductor will ( a ) double, ( b ) not change, ( c ) halve, ( d ) quadruple.

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