I have this question which I need to solve . But I am unable to. Suppose I have a current ring of radius R and current I (constant). at a distance x from the centre of the ring, I have a iron disk (radius r and thickness t) present in the plane of the ring. This disk will be attracted to the ring due to magnetisation. How do I calculate the force it experiences due to the field? Should I use F = ∇(m · B)?? I just want a way to solve it not the complete solution.. Any help is appreciated.