A semicircle of radius a is in the first and second quadrants, with the center of curvature at the ori- gin. Positive charge +Q is dis- tributed uniformly around the left half of the semicircle, and negative charge -Q is distrib- uted uniformly around the right half of the semicircle . What are the mag- nitude and direction of the net electric field at the origin pro- duced by this distribution of charge?