Problem 5

  The drawing shows three identical rods (A, B, and C) moving in different planes. A constant magnetic field of magnitude 0.45 T is directed along the +y axis. The length of each rod is L = 1.3 m, and the speeds are the same, v_A = v_B = v_C = 2.7 m/s. For each rod, find the magnitude of the motional emf, and indicate which end (1 or 2) of the rod is positive.

SOLUTION:

A: The emf is zero because the velocity of the rod is parallel to the direction of the magnetic field, so the charges experience no force.

B: The emf is vBL = (2.7 m/s)(0.45 T)(1.3 m) = 1.6 V. The positive end is end 2.

C: The emf is zero because the magnetic force on each charge is directed perpendicular to the length of the rod.