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Understanding RC and RL circuits

  1. Mar 30, 2009 #1
    Hi everyone. I am having trouble understanding RC AND RL circuits. Specifically the charging and discharging of circuits. The current and charge that goes through the inductor or capacitor at various time(At time=0 or some time after the switch is closed or a long time after the switch is closed).
  2. jcsd
  3. Mar 30, 2009 #2


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    Science Advisor
    Homework Helper

    Hi there! :smile:

    I'm sorry to hear you're driedup … you need to get a nice little bowl like mine :wink:
    Inductors are difficult. Capacitors are easier.

    Concentrate on understanding the process with just a capacitor first.

    See the PF Library or wikipedia …

    what part is worrying you? :smile:
  4. Mar 30, 2009 #3


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    Staff: Mentor

  5. Mar 30, 2009 #4


    Staff: Mentor

    I usually just remember the following rule of thumb:

    At DC a capacitor is an open circuit and an inductor is a short circuit.

    The corolary is that for very high frequencies a capacitor is a short and an inductor is an open circuit.

    So when you first throw the switch you apply the high-frequency corolary. The capacitor is a short so all of the voltage is across the resistor and the current is given by Ohm's law. After a while it settles down and you apply the DC rule. The capacitor is an open circuit so all the voltage is across it and there is no current.
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