18.7 Exercise 30

(a) Using the symmetry of the arrangement, determine the direction of the electric field at the center of the square in the figure, given that $q_{a} = q_{b} = - 1 . \text{00} \mu\text{C}$ and $q_{c} = q_{d} =+ 1 . \text{00} \mu\text{C}$. (b) Calculate the magnitude of the electric field at the location of $q$, given that the square is 5.00 cm on a side.