A straight wire is bent into the shape shown.Determine the net magnetic force on the wire when the current I travels in the direction shown in the magnetic field
)
A)2IBL in the −z direction
B)2IBL in the +z direction
C)4IBL in the +z direction
D)4IBL in the −z direction
E)zero

Question

A straight wire is bent into the shape shown.Determine the net magnetic force on the wire when the current I travels in the direction shown in the magnetic field 
) 
A)2IBL in the −z direction 
B)2IBL in the +z direction 
C)4IBL in the +z direction 
D)4IBL in the −z direction 
E)zero

Quizplus · Accepted Answer

As the current I travels from bottom to top of the wire, using the right-hand rule, we can find that the magnetic forces on the horizontal sections of the wire cancel out because they are perpendicular to the magnetic field. Therefore, the net force acts only on the vertical sections of the wire. The magnetic force on each of the vertical sections is given by F = IlB, where l is the length of each vertical section. Since there are two vertical sections facing in opposite directions, the total force will be 2IlB. Also, using the right-hand rule, we can find that the direction of the force is upward for the left vertical section and downward for the right vertical section. Therefore, the net force will be 2IlB in the +z direction. Thus, the correct choice is B, 2IBL in the +z direction.

A Straight Wire Is Bent into the Shape Shown