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Electric field in capacitors

  1. Mar 25, 2010 #1
    1. The problem statement, all variables and given/known data
    In a capacitor, is the potential difference at the battery causing an electric field flow inside the wire connected to the two plates of the capacitor? But like at the negative terminal of the battery, the potential is zero, so does that mean that the negative plate of the capacitor is also zero and that means that the electrons will move so that the potential difference is zero between the two plates? But like apparently the electric field once equilibrium is reached becomes zero...why is that because I thought that there is still a potential difference in the battery? It says in my textbook that 'once this equilibrium is reached, a potential difference no longer exists between the terminal and the plate; as a result no electric field is present in the wire and the electrons stop moving.'


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 25, 2010 #2

    ehild

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    At the instant when you connect a plate of the capacitor to the negative terminal of a battery, electrons will be transferred to the plate till the potential on the plate is the same as that of the terminal. After this happens, there is no electric field inside the wire and the electrons stop moving. When you connect the other plate to the positive terminal, the same happens, but the electrons will flow away from the plate to the positive terminal of the battery and the plate takes the same potential as the positive terminal of the battery. This happens in a very short time, depending on the resistance of the connecting wires and the the value of the capacitance.
    After this short time, steady state is reached and the potential of one plate is equal to the potential of the terminal it is connected with. Therefore the potential difference between the plates is the same as the potential difference between the terminals, and this potential difference is determined solely by the battery.

    You can not measure potential itself, but potential difference only. With respect to infinity, with respect to the ground, or with respect to any point of an electric circuit. This reference point with zero potential can be the negative terminal of the battery.

    ehild
     
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