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Quick question about RLC circuits

  1. Nov 2, 2004 #1
    quick question about RLC circuits....

    Okay guys and gals.........

    I know this is a rather dumb question, but I dont have alot of reference material where I am at currently (I am in Kuwait as part of Operation Iraqi Fredom).......so if someone could give me an answer I would appreciate it.....

    I should really know this but I just cant remember the answer and Im having a brain fart at the moment...

    Here is the question....

    If we have a simple parallel LRC circuit with a DC source, what would the voltage be in such a situation?

    At DC the Capacitor behaves ideally like an open circuit and the inductor behaves ideally like a short circuit......so what exactly would happen in this situation?

    What would the Capacitor/Inductor voltage be?


    Last edited: Nov 2, 2004
  2. jcsd
  3. Nov 2, 2004 #2
    since the inductor is in short circuit mode, the voltage of capacitor n inductor should be zero. this circuit is shorted!! and this is not the purpose of RLC. RLC should be powered by an AC voltage in order to produce resonance response.
  4. Nov 3, 2004 #3


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    There is no current flow in an RC circuit with a DC source.

    The voltages on the inductor and resistor are zero. The voltage across the Capacitor is Vcc.
  5. Nov 3, 2004 #4
    Thanks for responding.....

    I realise that this is not the purpose of an RLC circuit..........but I was wondering what would happen at DC voltage.....

    You seem to be implying that in this case the short circuit of the inductor causes the voltages over the resistor and cap to be zero...while the inductor efferctively "shorts" out all other components....

    Is this conclusion correct?

  6. Nov 3, 2004 #5
    Hey enigma......thanks for the reply....

    Okay......so you are saying that the cap will have Vcc while the resistor and inductor have zero voltage.......since they are in parallel (at least it appears that they are) shouldnt they have the same voltage?

    Or is this specific situation different because of the behaviour of the components?

    Also.........are you saying that the inductor will have zero current flowing through it?

    Your conclusion seem to contradict the other reply in this thread.....

    Which one correctly describes the behaviour of this circuit?

  7. Nov 3, 2004 #6


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    There is some question about if you mean a parallel or serial configuration.
    And it depends on what period of time you are talking about.
    On initial turn on, current will flow in the resistor for either configuration.

    Enigma is giving the long term operation in serial configuration.
    Tmwong went for the parallel configuration.
  8. Nov 3, 2004 #7
    My original question was about parallel RLC circuits.....

    But this answer will do also.....

    So you are saying that for a series RLC combination at DC, after a long time the open circuit of the capacitor will cause no current to flow in the circuit....

    While for the parallel RLC combination at DC, after a long time the short circuit of the inductor will cause zero voltage across all components since the circuit is shorted.

    So in one case (series RLC at DC)the open circuit takes most of the voltage drop and prevents current flow......

    And in the other case (parallel RLC at DC) the short circuit shorts out the entire circuit causing current to flow but with very little voltage drop across the components.

    Am I understanding your answer correctly?

  9. Nov 3, 2004 #8


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    You seem to have it right.
  10. Nov 3, 2004 #9


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    Ah. Yes, yes. Sorry.

    I was doing work with series RLC circuits this summer and had them on the brain, apparantly. Everything I said is incorrect for parallel RLC's.
  11. Nov 4, 2004 #10

    Ah.....good then.

    This was what I expected would happen at DC, but I wanted to ask someone to make sure.......Im glad my original answer seems correct.

    Thanks for the confirmation.

  12. Nov 4, 2004 #11

    Thanks for the answer enigma.......this is what I originally thought but I wanted to get other opinions to make sure I wasnt screwing it up....

    You say you were working with series RLC circuits.....was this for work or are you a professor at a university?

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