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https://en.wikipedia.org/wiki/Electrostatics says that "This pressure tends to draw the conductor into the field, regardless of the sign of the surface charge."

Does this mean that if I place a charge inside a hollow conductor, then the charge will always try to shrink the conductor, irrespective of whether there are other charges outside the conductor, or if the conductor is earthed?

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The hollow neutral conducting sphere will experience an induced charge separation if there is a point charge in the cavity. If the charge is negative, then

  • negative charge in the neutral conductor is repelled and will move far away.
  • Positive charge is attracted and moves closer.

So the inside surface will be positively charged and the outside surface negatively. And since electrostatic force decreases with distance, the inside is pulled in more strongly than the outside is pushed away. So yes, the charge in the cavity is trying to compress the sphere.

If it is earthed makes not difference. Then the outside charge is just able to move away from the sphere, and the inside will be able to acquire even more positive charge.

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  • $\begingroup$ I see, that's right it makes sense. Another question on what you said, will the negative induced charge that is on the surface, experience any force from the inside negative charge at all? Will it not be shielded? $\endgroup$ – Shodai Jun 7 '16 at 12:11
  • $\begingroup$ In my understanding, the force the surface feel is not from the negative charge on the cavity but from the induced surface density itself. I'm not sure about the inner urface but my guess is that, it will be attracted by the negative charge the same amount it is repealed by the positive surface density itself. $\endgroup$ – MarcoCiafa May 18 '20 at 23:22

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