A point charge Q is placed at the center of the line joining two equal point charges +q and +q . The value of Q if the system of the charges is equilibrium, is

Step-by-step solution

The forces on charge Q due to the other two charges will be equal and opposite and hence it will be in equilibrium. Force on + q due to the other two charges should also be equal and opposite. Their magnitudes will be equal if aligned & 1 4 ₀ q ^2 r ^2 = 1 4 ₀ qQ ( r 2 )^2 = 1 4 ₀ 4 qQ r ^2 & q =4 Q or Q = q 4 aligned Q must be negative, hence Q =- q 4