A flat circular loop of wire is in a uniform magnetic field of $0.30 \mathrm {~T}$. The diameter of the loop is $1.0$ $\mathrm { m }$, and a 2.0-A current flows in it. What is the magnitude of the magnetic torque on the loop when the plane of the loop is parallel to the magnetic field?
A) $0.00 \mathrm {~N} \cdot \mathrm { m }$
B) $0.47 \mathrm {~N} \cdot \mathrm { m }$
C) $0.52 \mathrm {~N} \cdot \mathrm { m }$
D) $0.41 \mathrm {~N} \cdot \mathrm { m }$

Question

Quizplus · Accepted Answer

The magnetic torque on a current loop is given by $\tau = NIAB \sin \theta$, where $N$ is the number of turns in the loop, $I$ is the current in the loop, $A$ is the area of the loop, $B$ is the magnetic field strength, and $\theta$ is the angle between the normal to the loop and the magnetic field. In this case, the loop is flat and parallel to the magnetic field, so $\theta = 0$ and $\sin \theta = 0$. Therefore, the magnetic torque on the loop is zero.

A Flat Circular Loop of Wire Is in a Uniform 0.30 T0.30 \mathrm {~T}0.30 T

A Flat Circular Loop of Wire Is in a Uniform $0.30 \mathrm {~T}$