1. The problem statement, all variables and given/known data Q a) A charge is placed at a distance x from the center of a conducting sphere of radius R.Find the charge flown through the switch(from ground) when it is closed . b) In the above question replace the switch with an ammeter .What is the reading of ammeter if charge is at distance 2R from sphere and charge is moved with velocity v towards sphere ? 2. Relevant equations 3. The attempt at a solution The charge Q will induce charges on the sphere .Before the switch is closed the potential at the sphere is entirely due to the charge Q,i.e positive potential at the sphere .When the switch is closed the potential on the sphere changes from positive to zero.For that net charge on the sphere must change from initial value zero. But how will we calculate the potential by charge Q at the sphere .Which point should we use because all points within the sphere are equipotential ? Any point on the surface is as good a candidate as the center or any other point. We may use center of the sphere as its distance from the charge is given .But why not some other point ? I would be grateful if somebody could help me with the problem.