# How does charge develop inside a spherical shell (with non-negligible thickness)?

I read that if there were a charge $$+q \$$ kept inside a spherical conducting shell of thickness $$t$$, a charge of $$-q \$$ would develop on the inner surface of the shell. Not more, not less.

Why is this so? Why doesn't the charge accumulating on the inner surface depend on the geometry of the conductor? Why wouldn't the charge on the inner surface be different if I changed the radius of the shell?