What effect does an external magnetic field have on a current-carrying loop?

When a current-carrying loop is placed in an external magnetic field, the interaction between the magnetic field and the electric current creates a torque on the loop. This phenomenon is a direct result of the Lorentz force, which states that a current-carrying conductor experiences a force when in the presence of a magnetic field. The direction of this force can be determined using Fleming's left-hand rule, which indicates that it acts perpendicularly to both the current and the magnetic field.

As the magnetic field exerts forces on the sides of the loop, these forces create a torque that tends to rotate the loop. The amount of torque produced depends on several factors, including the strength of the magnetic field, the amount of current flowing through the loop, and the area of the loop. If the magnetic field is uniform and the loop is made of a conductive material, this effect becomes even more pronounced.

This principle is fundamental in devices such as electric motors, where the rotation induced by torque allows for mechanical work to be performed. The current-carrying loop's response to an external magnetic field exemplifies many core concepts in electromagnetism and electromechanical systems. Other options, such as the loop not being affected or producing no torque, do not