A Flat Rectangular Loop of Wire Is Placed Between the Poles

Multiple Choice

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions $w = 0.60 \mathrm {~m}$ and $L = 1.0 \mathrm {~m}$ , and carries a current $I = 2.0 \mathrm {~A}$ in the direction shown. The magnetic field due to the magnet is uniform and of magnitude $0.80 \mathrm {~T}$ . The loop rotates in the magnetic field and at one point the plane of the loop makes a $30 ^ { \circ }$ angle with the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?

A) $0.83 \mathrm {~N} \cdot \mathrm { m }$
B) $0.30 \mathrm {~N} \cdot \mathrm { m }$
C) $0.40 \mathrm {~N} \cdot \mathrm { m }$
D) $0.96 \mathrm {~N} \cdot \mathrm { m }$
E) $0.48 \mathrm {~N} \cdot \mathrm { m }$