Three charges are located at three corners of a square as shown in the figure. [ Answer in 3 significant figures] -1.0 JC 4 cm 4 cm 2.0 JC -3.0 JC a) [12 pts] How much work is required to bring in a fourth charge (q4=+4.0 uC) to the last corner of the square at constant speed? b) [13 pt] What is the net electric field magnitude and direction at the center of the square due to the four charges? c) [5 pts] Sketch the electric field for the system (you need to have at least 5 field lines for the smallest charge)