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Question:

R-L Circuits and inductors?

I can't quite seem to understand how to solve this set of problems:A 12.0 V dc battery having no appreciable internal resistance, a 150 Omega resistor, an 11.0 mH inductor, and an open switch are all connected in series. 1.)After the switch is closed, what is the time constant for this circuit ?2.)After the switch is closed, what is the maximum current that flows through it ?3.)What is the current 73.3 microsecond after the switch is closed ?4.)After the switch is closed, what is the maximum energy stored in the inductor?------I got the answer to number one.but i don't understand why its 73.3 microsecond rather than 7.33 micro second. And i can't get the right answers for the rest of the questions even though I've tried using all the equations.

Answer:

1) time constant T L/R T 11*10^-3/150 T 7.33*10^-5 s T 73.3*10^-6 s T 73.3 us 2) After a long time the inductor will appear to be a short circuit, and the maximum current is I V/R I 12/150 I 0.08 A 3) i Io*(1 - e-t/T) i 0.08*(1 - e-73.3/73.3) i 0.05 A 4) W L*I^2/2 W 11*10^-3*(0.08)^2/2 W 0.0000352 J

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