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S E C T I O N 3 2 . 2 • RL Circuits 1009 where ! is the emf of the battery and I 0 " ! /R is the current at the instant at which the switch is thrown to b. If the circuit did not contain an inductor, the current would immediately decrease to zero when the battery is removed. When the inductor is present, it opposes the ! L " # L (dI/dt) is now positive. I t /R ε Active Figure 32.7 Current versus time for the right-hand loop of the circuit shown in Figure 32.6. For t * 0, the switch S is at position a. At t " 0, the switch is thrown to position b, and the current has its maximum value ! /R. At the Active Figures link at http://www.pse6.com, you can observe this graph develop after the switch in Figure 32.6 is thrown to position b. Quick Quiz 32.2 The circuit in Figure 32.8 consists of a resistor, an induc- tor, and an ideal battery with no internal resistance. At the instant just after the switch R L ε S Figure 32.8 (Quick Quiz 32.2) Figure 32.9 (Quick Quiz 32.3) Quick Quiz 32.4 Two circuits like the one shown in Figure 32.6 are identical except for the value of L. In circuit A the inductance of the inductor is L A , and in cir- cuit B it is L B . Switch S is thrown to position a at t " 0. At t " 10 s, the switch is thrown to position b. The resulting currents for the two circuits are as graphed in Figure 32.10. Quick Quiz 32.3 The circuit in Figure 32.9 includes a power source that provides a sinusoidal voltage. Thus, the magnetic field in the inductor is constantly S L Iron bar |