Two parallel rails of a railway track insulated from each other and with the ground are connected to a millivoltmeter. The distance between the rails is one meter. A train is travelling with a velocity of 72 km/h along the track. The reading of the millivoltmeter (in mV) is : (Vertical component of the earth's magnetic induction is $2 \times 10^{-5} T)$

Question

$$\begin {array} {1 1} (a)\;1.44 & \quad (b)\;0.72 \\ (c)\;0.4 \; & \quad (d)\;0.2 \end {array}$$