Four charged particles rest at the corners of a square of side a = 0.30 m. Charges 1 through 4 are 10, 20, 30 and 40 µC, respectively. Particle 1 is at the top left of the square, and the other charges are located counterclockwise from that charge.
a. Determine the electric field at the position of particle 3 as well as the electric force on particle 3.
b. Determine the electric field at the center of the square.