Question

In Fig. the bar AC has a mass of 50 g. It slides frictionlessly on the metal strips 40 cm apart at the edges of the incline. A current I flows through these strips and the bar, as shown. There is a magnetic field `|B_x| = 0.02 T` directed in the -y direction. How much must I be if the rod is to remain motionless? Neglect the slight overhang of the rod.

Answer 1

Magnetic force is along the positive x-axis. If motion is to occur
along the incline, `sumF=0:IL|B_y|cos37^@=mgsin37^@` from
which
`I=(mg tan37^@)/(L|B_y|)=((0.050)(9.8)(0.75))/((0.40)(0.02))=46A`