1. The problem statement, all variables and given/known data A cone made of insulating material has a total charge Q spread uniformly over its sloping surface. Calculate the energy required to take a test charge q from infinity to apex A of cone. The slant length is L. 2. Relevant equations 3. The attempt at a solution Potential at the tip of the cone is calculated by adding potentials due to rings of charges . Let us consider a ring having charge 'dq' at a distance 'x' from the tip and at slant height L'. L'=xsecθ where θ is the half angle of the cone . The surface area dS of the ring = 2π√(L'2-x2)dx dq=Q(dS)/(πRL) V = ∫dV = ∫kdq/L' This doesn't give me correct answer .I am not sure if I have approached the problem correctly. I would be grateful if somebody could help me with the problem.