Question

The two rails of a railway track, insulated from each other and the ground, are connected to a millivoltmeter. What is the reading of the millivoltmeter when a train travels at a speed of 20 m/sec along the track, given that the vertical component of earth’s magnetic field is 0.2 × 10^–4wb/m² and the rails are separated by 1 metre

• A. 4 Mv
• B. 0.4 Mv
• C. 80 mV
• D. 10 Mv

Answer 1

Answer: (B)

0.4 Mv

Answer 2

When a train runs on the rails, it cuts the magnetic flux lines of the vertical component of earth’s magnetic field. Hence a potential difference is induced between the ends of it’s axle. Distance between the rails l = 1m.

Speed of train $v = 36\frac{km}{hour} = \frac{36 \times 1000}{3600} = 10m/sec$By using e = Bvl ; e = 0.2 × 10^–4 × 20 × 1 = 4 × 10^–4 volt = 0.4 mV