Question

To find the torque on a current carrying flat loop of wire in a uniform magnetic field you need to multiply the current times the cross product of the area vector of the loop with the magnetic field vector -- I ( A x B ). How would you determine the magnitude and direction of the area vector A ? What would happen to the loop if it were placed in the magnetic field with A perpendicular to B and were free to move? If you were making an electric motor and wanted to loop to keep rotating, in simple terms, what would you do.

Answer 1

Magnitude of area of loop is found using simple geometry, means using formula for the area of loop whether it is a circle, square or rectangle. Its direction is given by a normal drawn at the plane of the loop.

When loop is placed in the magnetic field such that its plane is perpendicular to the magnetic field, than direction of area vector becomes parallel to magnetic field so torque acting on it becomes zero. But if area vector is perpendicular to magnetic field, it experiences maximum torque.

In case of electric motor, to rotate the loop completely, there should be a split ring assembly attached with this loop.