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After 14ms the current drops -- Find the capacitance at C

  1. Apr 26, 2017 #1
    1. The problem statement, all variables and given/known data
    IMG_20170426_121636.jpg Here is what I have so far. Am I going the right direction?
    If so, how do I go about finding the total current?

    2. Relevant equations
    See photo above.

    3. The attempt at a solution
    See above.
     
  2. jcsd
  3. Apr 26, 2017 #2

    cnh1995

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    Homework Helper

    Is that what you are asked?
     
  4. Apr 26, 2017 #3

    gneill

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    Staff: Mentor

    You are given two values for the current at different times. You'll want to use them at some point...

    What kind of circuit is this? If you simplified the circuit, combining the capacitors and combining the resistors, what are you left with? What kind of behavior would you expect when the switch closed? What's the general formula for the current with respect to time for such a circuit?
     
  5. Apr 26, 2017 #4
    Well, since the resistors are in series you can combine them to equal one resistor with a resistance of 3+1= 4kOhm.
    The capacitors in parallel would equate to one capacitor with 3+C= (3+C)microFerrads.
    Current with respect to time would be = Q/Δt ?
     
  6. Apr 26, 2017 #5

    gneill

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    Staff: Mentor

    Yes, so you have a basic RC circuit (resistor - capacitor circuit).
    Your class notes or textbook should show a general formula for the charge or voltage or current with respect to time for such a circuit. If not, do a web search on "RC circuit discharge". Here's an example hit:

    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html
     
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