question_answer

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                                         [MP PET 1993]

A)            Zero in vertical position 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

Correct Answer: B

Solution :

                   If player is 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.