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RC Circuit charging question

  1. Dec 2, 2015 #1
    1. The problem statement, all variables and given/known data
    Switch http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c27/math/math152.gif in Fig. 27-63 is closed at time http://edugen.wileyplus.com/edugen/courses/crs7165/halliday9781118230725/c27/math/math164.gif, to begin charging an initially uncharged capacitor of capacitance 15 microfarads through a resistor of resistance 20 ohms. At what time is the potential across the capacitor equal to that across the resistor?
    Figure 27-63
    Problems 57 and 96

    2. Relevant equations

    3. The attempt at a solution
    The answer winds up being .208 ms. so I am just looking for an answer. I want to know how to solve this. I tried using ohms law to figure out what the voltage is across R but of course that was a dead end because the emf is not given. next I tried iR=vmax(1-e^-t/RC). Again a dead end. Also I know that when the capacitor is fully charged the current is zero, hence the voltage across R will also be zero but I couldnt figure out how to implement that knowledge into a solution. Any help would be greatly appreciated.

    Attached Files:

    Last edited: Dec 2, 2015
  2. jcsd
  3. Dec 2, 2015 #2


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    None of the links to your figures are working.
  4. Dec 2, 2015 #3
    I just uploaded another pic. In case that one doesnt work, the circuit is just an RC series circuit with a battery and a switch.
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