Solution: Each charge applies a force on each other charge. There are, therefore, six forces, two at each vertex of thetriangle. The tension on a string is due to all forces acting along the string. These are shown in Figure 3.9b. The electric fieldintensity at the center of string A–B is due to the charge at C only since charges at A and B produce electric field intensities inopposite directions at point P and they cancel each other: