Two very long straight parallel wires carry steady currents i and 2i in opposite directions. The
distance between the wires is d. At a certain instant of time a point charge q is at a point
equidistant from the two wires in the plane of the wires. Its instantaneous velocity

\[\overrightarrow{v}\]

is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is :-