Two charges, each equal to q, are kept at x = – a and x = a on the x–axis. A particle of mass m and charge q0 = q/2 is placed at the origin. If charge q0 is given a small displacement (y << a) along the y–axis, the net force acting on the particle is proportional to
y
–y
$\dfrac{1}{y}$
–$\dfrac{1}{y}$