4. (18%) (a) Two charges with charge 6x10-5C and 2x10-5C are located at points P and Q respectively as shown in Figure 1. The distance between point P and point Q is Y m and distance between point Q and point R is X m. 6x10-5C P Ym 2x10-5 Q Xm R Figure 1. (a)(i) What is the magnitude of force exerted on charge at point Q by the charge at point P if Y = 1. (3) (a)(ii) If we place another charge of 3x10-5C at point R, what is the net force experienced on charge at Q by the other 2 charges at points P & R if X = 0.5? (5) (a)(iii) What is the total electric field at point Q produced by other 2 charges at point P and R? (3) (b) Two parallel plates are separated by 26mm apart. The potential difference between the two plates is 6.4V. What is the electric field strength between these two plates? (3) (c) Two charges separated by distance 2m have electrostatic force 12N between them. How large is the electrostatic force if the distance between them is halved? (4)