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Capacitor Electric Field

  1. Feb 16, 2009 #1
    Hi guys,

    This has bugged me for a while, if we have a battery (+ve) connected to one side of capacitor, and negative connected to ground. We are left with a wire coming from the other side of the capacitor. Is there a potential, and hence an electric field, between the wire and ground?

    Assuming the wire is a about 1 meter long (not in the immediate vicinity of the capacitor).

  2. jcsd
  3. Feb 16, 2009 #2


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    Yes there is. Conceptually you have two capacitors in series, the parallel plate one and the one formed by the wire hanging above the ground.
  4. Feb 16, 2009 #3
    Any piece of wire has capacitance,inductance as well as resistance. Often all three are largely ignored in elementary physics and electrical circuits because they are so small...

    But at very high frequencies or when information transmission rate is important such factors may become become critical. That's one reason why for several decades making circuits and components smaller has enabled us to make them faster...less delay considering the speed of electrical transmission, for example.
  5. Feb 16, 2009 #4
    Thats what I thought, but I'm not clear as to the charge distribution on the wires.

    The electric field (induced by the potential of the battery), exists in the dielectric between the capacitor (plate capacitor). The electrons arrange themselves on either plate to set up this field. Where do the electron in the wire arrange themselves? In particular, on the wire on the side of the capacitor not connected to anything. Also, the electrons at ground, how do they arrange themselves?

    If we had a 10V battery, and placed a test charge (1 electron) at ground (not touching) in between the free wire and ground, what kind of field would it feel?

    For arguments sake lets say the plate capacitor is 0.5microFarads.

  6. Feb 16, 2009 #5
    On the positive battery wire there is a dearth of electons, a positive charge; this attracts electons, weakly, on another wire or ground side...a few electrons gather....a weak field is established...

    In general ,a capacitance is directly proportional to plate (or wire) area area and inversely proportional to distance between plates (wires). The capacitance of the wires is small because there is a small area for electrons to gather and because the distance between is large.
  7. Feb 17, 2009 #6
    Good, so the capacitance between the wires in this case would be very small right? And the E-fied would exist between the plate capacitor (mainly). So an electron in betwen ground and the exposed wire does not really feel much force.

    Does this sound reasonable?
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