As shown in the figure, I have a hollow shell which contains a charge at its centre and another charge is placed outside the shell (some distance apart).
I know that the situation this figure depicts is NOT in electrostatic equilibrium as, of course the field inside the conducting material is not zero, the charges will flow in such a way that the resulting field due to induced charges will exactly CANCEL out the field due to other charges.
What is don't understand is that inside the sphere (the region which is not filled with conducting material) there will be no contribution of the field due to the charge placed outside the shell (I was told this by my instructor) so the force on charge placed at centre is zero.
I can't deduce a reason for this fact. I want to understand why this happens. Any help will be appreciated.