The two rails of a railway track, insulated from each other and from the ground, are connected to a millivoltmeter. What will be the reading of the millivoltmeter when a train travels on the track at a speed of 180 km h^–1? The vertical component of earth’s magnetic field is 0.2 × 10^–4 T and the rails are separated by 1 m.

Given:

Vertical component of earth’s magnetic field B=0.2× 10^-4T

Speed of train v=

Separation between rails l=1m

We know that,

motional emf produced due to a conductor of length l moving with velocity v in a magnetic field B is given by

…. (i)

Since v⃗ and B⃗ are perpendicular and their cross product is parallel to l⃗, eqn.(i) reduces to

Putting the values of v, B and l we get,

Therefore, the reading of millivoltmeter is 1mV