817_Physics ProblemsTechnical Physics

817_Physics ProblemsTechnical Physics - Chapter 28 (c) When...

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Chapter 28 157 (c) When the switch is opened, the branch containing R 1 is no longer part of the circuit. The capacitor discharges through RR 23 + bg with a time constant of RRC 15 0 3 00 10 0 0 180 += + = af .. . . k k F s ΩΩ µ . The initial current I i in this discharge circuit is determined by the initial potential difference across the capacitor applied to + in series: I V IR i C = + = + = + = 2 333 15 0 15 0 3 00 278 A k k A . . FIG. P28.71(c) Thus, when the switch is opened, the current through R 2 changes instantaneously from 333 A (downward) to 278 A (downward) as shown in the graph. Thereafter, it decays according to II e e t Ri tR RC t 2 278 0 0180 == > −+ f o r s . . (d) The charge q on the capacitor decays from Q i to Q i 5 according to qQ e Q Qe e t t i i i t t = = = = 5 5 5 180 0 180 5 290 a f . . ln .l n s s ms s m s *P28.72 (a) First let us flatten the circuit on a 2-D plane
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