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Homework Help: Calculating the time constant?

  1. Mar 28, 2012 #1
    1. The problem statement, all variables and given/known data
    I attached a picture of the RC circuit. The question asks to find the current as a function of time for light bulb 3 (R3). I know that I=Ioet/RC where Io is the initial current that runs through R3 but what about the R in the time constant RC? Is this resistance the total resistance of the circuit or is it just the resistance in R3?

    Attached Files:

  2. jcsd
  3. Mar 28, 2012 #2
    Do R1 and R2 have any effect on the current through C?
  4. Mar 28, 2012 #3
    Hmmm no, I think I kind of get it now, so the capacitor only affects anything on the outer loop. So the resistance I would use is just R3 right?

    (PS I forgot to mention the the switch is closed)

    Now let's say instead of a switch we had an extra resistor R4. Would that mean the R in t=RC would be R3+R4 since the capacitor is affected by both resistors that are in series?
  5. Mar 28, 2012 #4
    huh? :O
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