Could someone remind me of what we mean by zero electric field “inside” a conductor?

Question

If I have a spherical conductor (perhaps a shell) and "inside", as in the hollow area there is nothing. The electric field is 0. But what happens if there is a charge "inside" (not like inside the conductor, but in the hollow region) or some type of insulator with a nonzero net charge? Would there exist a field?

I drew a picture to illustrate. Not to scale by the way

Answer 1

For a static situation (i.e. no charges moving or current flowing) the net electric field is always zero inside of a conductor. Where by 'inside' I mean actually inside the material itself, not a region of free space that is simply enclosed by the material. The reason for this is, say there is an electric field $\vec{E}_0$, applied to the conductor- by definition there is an essentially infinite well of free charge that can move. This charge will move in response to the applied electric field and set up its own induced field, $\vec{E}_{ind}$. This field will oppose the orignal field and charge will keeping moving until it reaches equilibrium such that $\vec{E}_0+\vec{E}_{ind}= \vec{E}_{net} = 0 $. In practice this happens almost instantaneously. Above I haven't mentioned anything about shapes or charges outside the conductor so this holds for all static electric field configurations, including the one you describe above.