Question

Kindly answer with explanation and I beg you no spam.

Answer 1

Answer:

(b)

Explanation:

Force on -q due to each 4q charges = k(4q)(q)/a² (attractive in nature)

As the forces are equal and opposite, -q charge is in stable equilibrium.

Force on 4q due to -q charge =  k(4q)(q)/a² = 4kq²/a² (Attractive)

Force on 4q due to other 4q charge = k(4q)(4q)/(2a)² = 16kq²/4a² = 4kq²/a² (Repulsive)

As the forces are equal and opposite, the net force on each 4q is also 0. Hence, they are also in stable equilibrium.

Stable equilibrium - State in which Net force acting on the particle is zero and when small force is applied in any direction, the restoring force tends to move it back to its original position.