A point charge 'Q' is placed at the centre of the line joining two equal charges '+q' and '+q'. The value of 'Q' when the system is in equilibrium is

Step-by-step solution

Let the two equal charges +q be placed at a distance r from each other. The charge Q is placed at the centre, so its distance from each +q charge is r 2 . For the system to be in equilibrium, the net force on each charge must be zero. The net force on the central charge Q is zero for any value of Q due to symmetry. For the charge +q to be in equilibrium, the force exerted by the other +q charge must be equal and opposite to the force exerted by Q . The force on +q due to the other +q is F₁ = 1 4 ₀ q^2 r^2 . The for