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Homework Help: Basic capacitor question

  1. Aug 14, 2010 #1
    1. The problem statement, all variables and given/known data
    I have just started learning about capacitors and my question is when you have a DC voltage source connected in a circuit which also has a resistor and capacitor all in series, i.e. a basic charging circuit, is this circuit complete, since there is an air gap or non conductive dielectric in the capacitor there will no flow of current. Lets say to the same circuit we connect a light bulb in parallel to the capacitor than the capacitor will discharge and the light bulb will light up and than go off again. How this be possible if there is no flow current in the circuit since DC current cannot pass through capacitors. How is the circuit formed in this case.
    Code (Text):

    -------R-----
    |                |
    V               C
    |                |
    -------------

    -------R------------
    |                |        |
    V               C      Bulb
    |                |        |
    --------------------
     


    2. Relevant equations



    3. The attempt at a solution
    So in the case of capacitor charging i.e. without the light bulb there will be no current flow in the circuit because the capacitor will not pass DC current, i.e current across resistor R will be zero and in the case of capacitor discharging the current will also be zero since DC current does not flow through capacitor. When you put a capacitor in the DC circuit are you not just creating a break in the circuit than how can this circuit function, i.e. we do not have flow of electrons. The question is what am i missing to understand how the capacitors behave in a DC circuit and how is the circuit completed...
     
  2. jcsd
  3. Aug 14, 2010 #2
    Though current cannot flow through air gap/dielectric in the capacitor, charges can flow from both plates of capacitor (outwards) in to the circuit through R and V in order to charge the capacitor. So even in a DC circuit, current flows in the circuit (not through/inside the capacitor) when R and C is connected till C is charged to applied voltage V.
     
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