Current and Time in RL Circuit

  • Thread starter musiliu
  • Start date
  • #1
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Homework Statement



An emf of 10V is connected to the RL circuit (R = 10 Ohms, L = 1.0 H)
shown below for long, long time (the switch is in position 1). Then, at t = 0
the switch is thrown into position 2. Find the current in the circuit at t = 0.2
s. When will the current drop to 0.001 A?
[PLAIN]http://img132.imageshack.us/img132/5139/physicsproblem.jpg [Broken]

Homework Equations



"Discharge" of RL circuit: I(t) = I0e-Rt/L

The Attempt at a Solution



Part 1:
This looks like simple plug-in problem:
I0 = E / R after "long, long time"
E = 10 V, R = 10 Ohms, L = 1 Henry
I(0.2) = 0.135 A

Part 2:
I set I = .001 A and solved for t:
t = 0.691 s

Are my answers correct and did i do this problem correctly?
 
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Answers and Replies

  • #2
1,860
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What did you use as Io, how did you do part 2?
 
  • #3
44
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I used Io equal to E / R, voltage over resistance from Ohm's Law, because for "long, long time", the initial current is equal to that...

so is my answer correct?
 
  • #4
ehild
Homework Helper
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1,914
Your answers are correct.


ehild
 

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