Q155 / 160 · TS EAMCET 2005 · Physics

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 metre. A train is travelling with a velocity of $72 \mathrm{~km} / \mathrm{h}$ along the track. The reading of the millivoltmeter (in $\mathrm{mV}$ ) is (vertical component of the earth's magnetic induction is $2 \times 10^{-5} \mathrm{~T}$ )

  • A
    1.44
  • B
    0.72
  • Correct answer
    C
    0.4
  • D
    0.2

Solution

Induced emf, $e=B v l$ where, $\begin{aligned} v & =\text { velocity of train } \\ & =72 \times \frac{5}{18} \\ & =20 \mathrm{~m} / \mathrm{s} \\ & =2 \times 10^{-5} \times 20 \times 1 \\ & =2 \times 10^{-5} \times 20 \\ & =40 \times 10^{-5} \mathrm{v} \\ & =40 \times 10^{-2} \mathrm{mV} \\ & =0.4 \mathrm{mV} \end{aligned}$

Hence, the correct answer is option: 'C'.

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