1. The problem statement, all variables and given/known data A tiny, 0.60g ball carries a charge of magnitude 8.0 mircoC. It is suspended by a vertical thread in a downard 300 N/C electric field. What is the tension in the thread if the charge on the ball is (a) positive, (b) negative? 2. Relevant equations Fe=QE? 3. The attempt at a solution At first I thought the equation E=(kq)/(r^2) would be useful until I read that there was no radius. Also found that angle is not necessary. I'm completely clueless as to what equation to use. The book gives me the answer (a) 8.3 mN; (b) 3.5 mN.