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Can electric charge be enclosed ?

  1. Oct 16, 2004 #1
    Hi everybody

    I'm wondering if it is possible to enclose a relatively high electric charge in a non-conducting recipent (say plastic or glass -- macroscopic : centimeters) ?
    Is it possible technically ?
    if so, what is the limit amount of charge we can enclose ?
    if so, would the recipient stay uncharged externally : ie will the recipient attract opposite charges on its external surface OR will the global charge of the recipient stay different from 0 ?

    thanks,
    tabchouri

    PS:
    when I said "relatively high charges" I mean |q| > 10e-5
     
    Last edited: Oct 16, 2004
  2. jcsd
  3. Oct 18, 2004 #2
    To be much clearer:
    I meant an electrostatic charge (+ or -) that is in the center of a glass or plastic sphere: so that the overall charge of the object is not 0. I do not mean a capacitor as the overall electrostatic charge of capacitors is allways 0. Simply : an object that has (and won't lose) an overall electrostatic different from 0 (and in particular |q| > 1e-5),
    Can this be done (given current state of technology) ?
     
  4. Oct 19, 2004 #3
    You do not give units - do you mean 1e-5 coulomb? On a sphere 10 cm in radius the field at the surface would be 9e+6 V/m. Whether your charge configuration will be stable in the short run depends on the breakdown field of the insulator.

    Of course, things do get neutralized: corona, cosmic rays. After some time you will have a kind of Leyden jar with a compensating charge on the outside. In other words: a capacitor.

    A different limit is the mechanical strength of the material holding the charges together against their Coulomb repulsion. If a cluster or molecule gets too highly charged (by an Auger cascade for example), it will fly apart in fragments - a Coulomb explosion.

    PS: This seems off topic - what is the connection with quantum physics?
     
  5. Oct 19, 2004 #4
    Indeed, my question is pretty off topic, I'm sorry for that; but amongst the others, this sub-forum is the most suitable for it (I think)

    yes I meant a charge of 1e-5 coulomb,
    Assuming a sphere of 10 cm in radius made of glass, would it stand the field of 9e+6 V/m at its surface ? If not, is there any other insulator with high breakdown field that would stand it ?

    About the Leyden Jar effect, assuming that the sphere is in pseudo-vacuum (1e-6 torr inside a much bigger glass recipient), will we still have a capacitor after some time (concerning the little sphere, the external big recipient does not matter) ?

    Another silly question:
    In fact, I need some objects that will interact by great attraction or repulsion (1 to 10 Newton at a distance of 1 meter). That would be electrstatic charges or permanent magnets (neodymuim or other powerful ones). I think that force calculation and prediction for magnet is pretty complex (compared to electric charges). Besides, forces varies at 1/(r^3) for magnets.
    This explains my question.

    So here goes the silly new part:
    assuming a spherical capacitor (radius 10 cm) having in its center a charge +Q, and on the external surface another charge -Q, the global charge will be 0, just like a neutral atom.

    With all the shielding an insolation required, is there any configuration that will make the capacitor hold its charge for a very long time (1 year or longer), and more importantly, will this capacitor generate a net electric field outside the sphere (to have interactions between two capacitors).

    thank you very much for any help or remarks
     
    Last edited: Oct 19, 2004
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