Two rails of a railway track, insulated from each other and the ground, are connected to a millivoltmetre. What is the reading of the millivoltmetre when a train travels at a speed of 20 `ms^(-1)` along the track? Given that the vertical component of earth's magnetic field is `0.2xx10^(-4)"Wbm"^(-2)` and the rails are separated by 1 m