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Electric charge on conductors , capacitors

  1. Nov 14, 2013 #1
    Hi I'm wondering why does the charge resides on the plates on a capacitor when it's charged but not on say two closely placed wires or circuit traces etc, well I do understand that charges stay on capacitor plates because the opposite charges tend to attract and with a distance between them they stay as close as possible for as long as possible.

    So the question is more like , given the same amount of voltage does the charge accumulation depends on the conductor geometry or spacing between them ?
    Say I have a parallel plate capacitor and two wires with the surface area the same as that of the plates , and the gap between each of the wires just as big as that of the plates will they ahve the same capacitance or no?

    P.S. although I think it's impossible but would it be possible to make a capacitor which looses it's charge right after the source or the supply is taken away , well it wouldn't be a capacitor anymore but still , say I needed a device with which I can use + charge to attract some negative charge on the other plate but let it go just as when I disconnect the positive charge ?
    As upon disconnecting a capacitor it would discharge slowly.
  2. jcsd
  3. Nov 14, 2013 #2


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    the 2 "parallel wires of a circuit will have a charge on the for as long as there's a voltage applied
    Remove the voltage and the charge will dissipate out into the attached circuitry

    yes of course it is possible ... you just make a capacitor that has a very leaky dielectric between the plates so that current (charge) flows between the plates and balances out.
    This of course would be a VERY poor capacitor

  4. Nov 14, 2013 #3
    Two wires laying next to each other will have a small but non-vanishing capacitance that indeed depends on the exact geometry of the wires such as their sizes and distances. That means that small but non-vanishing charges might indeed build up in those wires. For most purposes these charges can be considered negligible (but not always). Excellent question.
  5. Nov 14, 2013 #4
    @davenn , well yes a poor capacitor would do , but the problem is I need a good isolation between the plate so no current (in theory) runs between them but so that when I switch the negative potential off of one of the plates the + doesn't linger on the other as it would normally do.
    The purpose is so that I could switch a negative potential on the legs of two capacitors in series so that i could get charges to run back and forth between them.
    The thing is with a normal capacitor I can't do that just because the cap needs to be discharged or drained to ground for it to reverse polarity.

    @dauto , why would that be an excellent question , just asking ? :)
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