Q. A player with $3\ m$ long iron rod runs towards east with a speed of $30\ km/hr$. Horizontal component of earth’s magnetic field is $4 \times 10^{- 5}Wb/m^{2}$. If he is running with rod in horizontal and vertical positions, then the potential difference induced between the two ends of the rod in two cases will be
A) Zero in vertical and $1 \times 10^{- 3}V$ in horizontal position
B) $1 \times 10^{- 3}V$ in vertical position and zero is horizontal position
C) Zero in both cases
D) $1 \times 10^{- 3}V$ in both cases
Explanation
(b) If player in running with rod in vertical position towards east, then rod cuts the magnetic field of earth perpendicularly (magnetic field of earth is south to north).
Hence Maximum emf induced is
$e = Bvl - 4 \times 10^{- 5} \times \frac{30 \times 1000}{3600} \times 3 = 1 \times 10^{- 3}\ volt$
When he is running with rod in horizontal position, no field is cut by the rod, so $e = 0$
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Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.