In the figure four particles form a square with edge length a = 2.21×10−2 m. The charges are q1 = q4 = 1.60×10−15 C and q2 = q3 = q. (a) What is q if the net electrostatic force on particle 1 is zero? (b) Is there any value of q that makes the net electrostatic force on each of the four particles zero? a) Number Units b)