(a) A particle carrying charge \(+q\) is located at the center of a square with sides of length \(\ell\). Given four particles, two carrying charge \(+q\) and two carrying charge \(-q\), how should you place them at the four corners of the square, with one particle at each corner, such that the vector sum of the electric forces exerted on the center particle is zero? 

\((b)\) If you leave the corner particles in the arrangement determined in part \(a\) but move the center particle to the midpoint of one side of the square, what are the magnitude and direction of the vector sum of the forces exerted on this particle?