Torque on current loop in a magnetic field
By When a current-carrying loop of wire is placed in a magnetic field, the loop experiences a torque, which tends to rotate the loop. The magnetic torque on a current loop is given by \begin{align} \tau= N A B \sin(\theta) \end{align} where $\tau$ is the torque in Newton-meters, $N$ is the number of turns in the loop, $A$ is the area of the loop in square meters, $B$ is the magnetic field strength in Tesla, and $\theta$ is the angle between the magnetic field and the normal to the plane of the loop.
The direction of the magnetic torque is perpendicular to both the magnetic field and the plane of the loop. If the loop is free to rotate, it will tend to align itself with the direction of the magnetic field.
The magnetic torque on a current loop is the basis of many important devices, including electric motors and generators.
