Thank for the reply, I don't know why I confused the total charge with the image point charge.
If you don't mind another rudimentary question, in the case of the sphere we find surface charge density by taking the gradient of the potential evaluated at the boundar, and to find total charge we...
For the charge +q inside, the induced charge on the boundary is -qR/p, so in a Gaussian surface outside shouldn't we see a charge equal to the sum of these and thus have electric field and potential difference?
Potential inside is given as in ,https://en.wikipedia.org/wiki/Method_of_image_charges, which is the sum of excitation and induced potential. When the charge is outside it is easy to argue potential is zero in the sphere. But when we have charge inside and image outside, what is potential...