Question

A 0.2 kg conductor of length 0.8 m carries 2 ampere current to the right in a magnetic field. What is the magnitude and the direction of the magnetic field acting on the conductor if the net force on the rod is zero? (Assume that the rod is hung by two insulating supports.)

Answer 1

if there is no net force, the magnetic force BIL equals the weight, M g.
Therefore
B = M g/(I L)
= 0.2*9.8/(2.0*0.8) = 12.25 T

The direction of the B field must produce an upward force. Use the right hand rule.

Answer 2

Selected Answer:
1.2 is the magnitude
Correct Answer:
Correct
Since the net force is zero, the weight of the rod should be balanced upward by the magnetic force on the rod. According to the right-hand rule, the magnetic field should be directed into the plane of paper and perpendicular to the direction of the current. Hence the weight of the rod should be balanced by the magnetic force.