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Homework Help: Some help with capacitors please

  1. Oct 2, 2009 #1
    At t=0 the switch S is closed with the capacitor is uncharged.

    .............. 3M ohm......... 102 micro F
    l l
    l ............... s........<----i--->....................l
    l-------l i-------/.--------------------------l
    17 V

    What is the charge on the capacitor when
    I = 2 mA? Answer in units of C.

    Need some help understanding it...
  2. jcsd
  3. Oct 2, 2009 #2


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    hello christianerik, welcome to PF

    you know that C=Q/V

    find the voltage between the resistance using the given values of current and resistance [since it’s connected in series with the capacitor, you should subtract this value from 17 volts to get the voltage between the capacitor plates]. then use the previous equation to solve.
  4. Oct 5, 2009 #3


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    christianerik, welcome to PF Forums! You will find many useful discussions and people willing to help you. Before we can do so, you need to show your own effort towards solving your problem. You may want to reread this https://www.physicsforums.com/showthread.php?t=94380" that is shown at the top of this topic. If you don't have a clue, start by stating all that you understand about your problem and lead us to the point where you are stuck.

    Using the homework template that is given, when you initiate a thread, is also helpful no only to us but it also helps you organize the question more clearly. Some good examples of homework threads may be viewed https://www.physicsforums.com/showthread.php?t=131568".
    Last edited by a moderator: Apr 24, 2017
  5. Oct 6, 2009 #4


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    Your drawing's not clear. I suggest sketching on paper, or using drawing software and uploading the image. Also recommend double-checking the values in your question, particularly for the resistor & current.
    Last edited: Oct 6, 2009
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