Figure shows a metal rod PQ resting on the rails AB and positioned between the poles of a permanent magnet. The rails, the rod and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = 180.0 $m\Omega$. Assume the field to be uniform.

The power required (by an external agent) to keep the rod moving at the same speed (= 12 $cms^{-1}$) when K is closed will:

$4.5 \times 10^{-3} W$

The correct answer is Option (3) → $4.5 \times 10^{-3} W$