I was reading about method of images from Griffiths and I was thinking about a situation where a charge is kept inside a spherical cavity of a conducting shell rather than placing it outside a conducting shell.
Here the Sphere is not grounded. Can I say that the charge Q is like a mirror charge to some other charge Q' to the right of the sphere? But the problem is, the sphere is not grounded. If I take Q to be the mirror charge of Q', then the potential at the surface of cavity becomes zero and that on the outer surface becomes non zero causing an electric field.
Given the position of Q (not at the centre of cavity), how will I locate the correct mirror charges?