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Homework Help: A circuit with capacitor and resistor

  1. Apr 8, 2004 #1
    A circuit with capacitor and resistor !!

    Dear all,

    it is a simple electric circuit include one capacitor and one resistor in parallel. about 25V is provided. Then i assume I1 cross the capacitor and I2 cross the resistor. Therefore, when a capacitor has a constant change, can i assume the I1 current flowing to zero, then I2 is V=RI ??

    thanks a lot !!
  2. jcsd
  3. Apr 8, 2004 #2
    It's kind of tricky, I'm gonna do my best here but you might want to wait for another answer.

    I think it depends on what you mean by "a capacitor has a constant change". If you mean that it's fully charged, then yes, the current through it would be zero. However it can mean that the capacitor is constantly charging and discharging at the same rate, so the charge of it stays the same but there is still current through it. I think the latter is what's happening in this case, since I don't see how a capacitor can be fully charged when it's connected in parallel with a battery and a resistor.
  4. Apr 9, 2004 #3


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    One little nitpick on the phraseology: voltage is across, current goes through. This seems nitpicky, but it will probably help you understand circuits better if you are strict with it.

    BTW, if you assume ideal components, then this situation obtains immediately, since an ideal capacitor would take 0 time to charge to any arbitrary voltage supplied directly from an ideal voltage source.
    Last edited: Apr 9, 2004
  5. Apr 29, 2004 #4
    One caveat, this is a purely theoretical situation as there is no voltage source with zero internal resistance and infinite current to produce a charged capacitor instantaneously.
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