Principle of superposition
Find the force on any one of the charges if three charges each of 5C is placed on the vertices of an equilateral triangle of side 3cm( figure) Let us consider the 5 C charge at B F 1 be the force acting on 5 C charge at B by A and F 2 be the force acting on charge B by charge at C since it is an equilateral triangle and all charges the same F 1 =F 2 = F from the figure these two forces F is inclined with each other at an angle of 60 0 (since equilateral triangle) • • • by the parallelogram law of forces resultant R =SQRT( F 2 + F 2 +2 FF cos60)=√3 F but F =(1/4πε 0 )(Q×q)/r -2 ie F =(1/4πε 0 )(5×5)/9×10 -4 F =9×10 9 ×25×10 4 /9=25×10 13 N The resultant force R ,on charge at B= 25√3×10 13 N ( the force on each charge on the other vertices also will be the same)