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IssacNewton said:sorry for the confusion.
By the way I have related question about this problem. If we have a cavity(of some weird shape) in spherical metal ball and if we place charge in it, then we of course have induced charge on the cavity walls and then we have equal but opposite charge
on the outer surface on the sphere. Now Griffiths in his books says that the charge
on the outer surface get distributed uniformly irrespective of the cavity shape and the
location of test charge inside the cavity. He didn't really offer any explanation for this.
What would be the reason ?
Going back to your question here, I think I can give you a better answer.
Put a Gaussian spherical surface around O, radius between R1 and R2. The E field everywhere over this surface is zero since it's in a metallic environment. So the charges at the outside surface (at R2) do not experience a radial force. That means that the only force exetrted on them is that due to their neighbors, i.e. all on the surface R2, and that obviously will distribute the charges so that there is uniform distance between them, in other words, uniform charge density.