A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E, as shown in the figure. It is placed in a uniform magnetic field of 0.55 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the force acting on section CD of this wire?
A) 0.066 N perpendicular into the page
B) 0.40 N perpendicular out of the page
C) 0.066 N perpendicular out of the page
D) 0.40 N perpendicular into the page
E) 0.20 N perpendicular out of the page

Question

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E, as shown in the figure. It is placed in a uniform magnetic field of 0.55 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the force acting on section CD of this wire? 
A) 0.066 N perpendicular into the page 
B) 0.40 N perpendicular out of the page 
C) 0.066 N perpendicular out of the page 
D) 0.40 N perpendicular into the page 
E) 0.20 N perpendicular out of the page

Quizplus · Accepted Answer

Using the right hand rule for a current-carrying wire in a magnetic field, the force on section CD is perpendicular to both the direction of the current and the magnetic field, and points out of the page. The magnitude of the force can be found using the formula F = I*L*B*sin(theta), where L is the length of section CD and theta is the angle between the current and magnetic field. Since both AB and CD are parallel to the magnetic field, theta = 0 degrees and sin(theta) = 0. Therefore, the force on section CD is F = I*L*B*sin(theta) = 0, and the answer is C (0.066 N perpendicular out of the page).

A Wire in the Shape of an "M" Lies in the Plane