1. The problem statement, all variables and given/known data A charge is placed at each corner of a square. The charges at the top corners are each +6μC and the ones at the bottom are each -4μC. Each side of the square has a length of 10.0 cm. Determine the electric field strength at the center of the square. 2. Relevant equations E = Kq/2a^2 3. The attempt at a solution I understand that the electric field at the center is the vector sum of the fields due to each of the point charges. I somewhat understand the problem if all the charges were the same, then the electric field strength would be 0. But I'm a little thrown with multiple charges. Is it: E = K(q1q2)/(2)(a^2) E = (9x10^9 Nm^2/C^2)*[(6x10^-6 C)(4x10^-6 C) / (2)(.01 m^2) E = 10.8 N/C Somehow I don't think so because this doesn't really give me N/C as the answer. So... considering it is supposed to be the vector sum.. am I just supposed to add the charges together? In which case q = (6μC+6μC+ (-4μC)+ (-4μC)) = +4μC?