A small sphere is charged uniformly and placed at some point A (xo,yo) so that at point B(9 m,4 m) electric field strength is E→=(54i^+72j^)NC−1 and potential is 1800 V. Then

E→=54i^+72j^,E=90NC−1 90=9×109Qr2                      ....(i) V=1800=9×109Qr           ....(ii)From Eqs. (i) and (ii), we getr=20m,Q=4μCNow,9−x0i^+4−y0j^20=54i^+72j^90 or  x0=−3,y0=−12