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My textbook says:

  • Inside a conductor, electric field is zero.
  • The interior of a conductor can have no excess charge in static situation.
  • Electric field just outside a charged conductor is perpendicular to the surface at every point.

I know that these laws are meant for solid conductors or in other words conducting materials alone. But if we had a hollow spherical conducting sphere maybe with air (or any insulator) as the medium inside the sphere, how would these laws be affected if a positive charge ( or any charge for that matter) is placed inside the sphere in air (static condition).

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The macroscopic electric field inside the 'metal' of the conductor is zero in electrostatic conditions. In a hollow cylinder , if a positive charge is place inside the cavity, the field is non zero inside the cavity.

Again, the interior of a hollow shell can hold the positive charge there, because of the induced charges on the inner wall of the cavity. These charges, nullify the field due to the positive charge inside the 'metal' of the conductor. The last conclusion is always true in electrostatic conditions, when the conductor becomes an equipotential.

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  • $\begingroup$ But then in that case, shouldn't the second assumption be invalid? As a Gaussian surface drawn within the conductor would enclose some net amount of flux? $\endgroup$ – LeroyJD Jul 28 '16 at 14:59
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    $\begingroup$ No, it wont, because that gaussian surface would include your test charge inside the cavity + the charge induced on the INNER surface of the cavity, which gives a total charge enclose = 0 $\endgroup$ – Lelouch Jul 28 '16 at 15:13
  • $\begingroup$ if there was a negative charge inside the hollow sphere and a positive charge on the surface of the sphere, the positive charges would still remain on the surface? If so, why aren't they attracted by the negative charge? $\endgroup$ – LeroyJD Jul 28 '16 at 16:57
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    $\begingroup$ because the field of the negative charge inside will not penetrate the METAL of the conductor to affects the charges on the outside(shielding). $\endgroup$ – Lelouch Jul 28 '16 at 17:00
  • $\begingroup$ However, if charges are induced in the inner wall, wouldn't an equal amount of charge be induced on the outer surface of the wall. This would produce an electric field unless the sphere is grounded from the outside which is not what i'm assuming. $\endgroup$ – LeroyJD Jul 28 '16 at 17:40

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