Question

A current-carrying rectangular loop of wire is placed in an external magnetic field with the directions of the current and field as shown in the diagram. Now if the loop were rotated so that the plane of the loop was parallel to the magnetic field lines, would there be a magnetic torque acting on the loop?

Answer 1

When a current-carrying loop is rotated to be parallel to the magnetic field lines, there is no magnetic torque acting on the loop.

Step-by-step explanation:

When a current-carrying rectangular loop of wire is placed in an external magnetic field, it experiences a torque. The torque can be calculated using the formula τ = IABsinθ, where τ is the torque, I is the current, A is the area of the loop, B is the magnetic field strength, and θ is the angle between the normal to the loop and the magnetic field lines. If the loop is rotated so that its plane becomes parallel to the magnetic field lines, the angle θ becomes zero, and the torque becomes zero as well.

This can be explained using the right-hand rule. The force on the loop is given by the cross product of the current vector and the magnetic field vector. When the loop is perpendicular to the magnetic field, the force is maximum, resulting in a torque. However, when the loop is parallel to the field, the cross product becomes zero, and no torque is exerted.

Therefore, if the current-carrying loop is rotated so that its plane is parallel to the magnetic field lines, there would be no magnetic torque acting on the loop.