Question

A very long cylindrical iron rod of radius R is given a uniform longitudinal magnetization M, and then bent into a circle with a narrow gap of length w (this is essentially a toroid with a circular cross section from which a very small portion of_________.

Answer 1

Answer: Magnetisation M which will produce magnetic field at the center of the gap.

Explanation:

A bound surface current will flow around the square cross section in the direction perpendicular to the field.

This is like a torus and a square loop with a current flowing the opposite way.