Final answer:
A rectangular loop of wire in a magnetic field will rotate due to the magnetic torque. The rotation's direction is determined by the current direction and the magnetic field's orientation. This motion is predicted by the right-hand rule and calculated with the torque formula τ = μ × B.
Step-by-step explanation:
The direction in which a current-carrying rectangular loop of wire will tend to rotate in an external magnetic field can be determined by the magnetic torque exerted on the loop. The magnetic torque on a current loop can be calculated using the right-hand rule, where your thumb points in the direction of the current and your fingers curl in the direction of the magnetic field B. The sides of the loop perpendicular to the magnetic field will experience forces that are equal in magnitude but opposite in direction, leading to a torque that tends to rotate the loop.
For a rectangular loop in a uniform magnetic field that is perpendicular to the plane of the loop, the torque will be maximum and tends to rotate the loop to align its plane parallel to the magnetic field. This torque can be calculated using the formula τ = μ × B, where μ is the magnetic dipole moment and B is the magnetic field strength.
In summary, the loop will rotate in a way that the magnetic moments align with the magnetic field lines. The direction of this rotation depends on the direction of the current through the loop and the orientation of the magnetic field.