Momento torcente in un anello di corrente in un campo magnetico

Consider a rectangular current-carrying loop of lengths a and b placed in a uniform magnetic field, with an axis of rotation passing through point O at distance m from one end.

The magnetic forces acting along the plane of the loop lie on the same axis passing through O; thus, the sum of their torques about the axis is equal to zero.

Similarly, the torques due to the forces perpendicular to the plane of the loop can be determined.

By adding all the torques acting on the loop, the net torque can be determined, where A is the area of the loop.

A current-carrying closed loop can be referred to as a magnetic dipole. The magnetic dipole moment is a vector quantity, where the magnitude is the product of the area and the current flowing through the loop; its direction is perpendicular to the plane of the loop, following the right-hand rule.

Therefore, the torque on a current loop due to a uniform magnetic field can be described in terms of the magnetic dipole moment.