1. The problem statement, all variables and given/known data I uploaded the Ex. 3.2. 2. Relevant equations 3. The attempt at a solution On the spherical surface, the potential due to q'' at center is going to be constant. q''= V0 R\k Let's say that the potential of the neutral conducting sphere is V0. Now, to calculate the force of attraction, I have to calculate potential due to both the image charges and the original charge in the region outside the sphere. For this I have to calculate q''. q'' is opposite to the charges induced on the sphere due to q. To calculate this induced charge, I have to differentiate V given in eqn. 3.17 wrt r, which will give the surface charge density (integrating which over the spherical surface will give the induced charge). Is there any other easier way to calculate this induced charge?