The particles are as follows: 10 uC at x = 0, y = 0; -5 uC at x = 20, y = 0; -15 uC at x = 20, y = 20; and 20 uC at x = 0, y = 20. Determine the force (magnitude and direction) on a 1 uC particle at the center of the square.
What is the electric field at the center of the square?