# When can charge reside on the inner surface of a conductor?

My confusion stems from the following exercise:

I've written sloppily: "Why are charges not induced on at least that portion of the inner surface?". As I ask, I don't see how the charge density on the interior of the hollow space is zero everywhere. Typically, at static equilibrium, (unless there's a cavity with a charge inside), a charged conductor's net charge will sit at the outer surface of the conductor. I don't know why, if a conductor has an empty cavity why charge on the conductor will sit on the outer surface rather the inner one. Will charge sit on the conductor's outer surface if it has no net charge? My guess is yes although there will be no net charge from these particles on the surface, but if it is a charged conductor, say with charge $$+Q$$, then all the positive charges making up this $$+Q$$ will sit on the outer surface.

With an empty cavity, I don't see how they couldn't theoretically sit on the inner surface, and in the instance below I don't see how this can't happen. As I've illustrated, the positive charge should polarize the conductor to some degree, with negative charges flowing towards it and positive charges flowing away to it. As such, I'd assume negative charge would collect on the half of the sphere closer to the $$+q$$ and more negative charge on the inner surface closer to the charge. This seems like what the charges would do given they can move freely within the conductor. Why is this wrong?