1. The problem statement, all variables and given/known data Find the points where the equipotential line is tangent to the thick black line 2. Relevant equations 3. The attempt at a solution I thought that it was A, G and K, because there, the electric field is horizontal and thus perpendicular to the black line and electric field is always perpendicular to equipotential line. However, I am getting the answer wrong. How do I approach this problem?