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  4. 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 1 m. A train is travelling with a velocity of 72 kmh -1 along the track. The reading of the millivoltmeter (in mV ) is (vertical component of the earth's magnetic induction is 2 × 10-5 T )

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Q. 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 $1 \,m$. A train is travelling with a velocity of $72 \,kmh ^{-1}$ along the track. The reading of the millivoltmeter (in $mV$ ) is (vertical component of the earth's magnetic induction is $2 \times 10^{-5}\, T$ )

Electromagnetic Induction

Solution:

Induced emf, $\varepsilon=B v l$
$v=\text { velocity of train }=72 \times \frac{5}{18}=20\, ms ^{-1}$
Induced emf, $\varepsilon=2 \times 10^{-5} \times 20 \times 1$
$=2 \times 10^{-5} \times 20=40 \times 10^{-5} V$
$=40 \times 10^{-2}\, mV =0.4\, mV$