1. The problem statement, all variables and given/known data A spherical shell of radius 'a' and charge Q is expanded to radius 'b'. What is the work done by the electrostatic force in this process? 2. Relevant equations Method 1 Work done = initial energy - final energy Method 2 Work done = Q (potential difference between the two positions) 3. The attempt at a solution Method 1 Initial energy of the spherical capacitor = Q*Q / 2C = Q*Q / 2*4*pi*E*a (E= permittivity of the medium) Final energy = Q*Q / 2*4*pi*b Work done = Q*Q / 2*4*pi*E [ 1/a - 1/b] Method 2 Initial potential = Q / 4*pi*E*a Final potential = Q / 4*pi*E*b Work done = Q*Q / 4 *pi* E* [1/a - 1/b] The two methods do not lead to the same answer. I need to understand why this is so. Would appreciate some tips. Thanks.