# Electromagnetism formula question

#### Kai Jie

Joined Jul 11, 2016
3
Is the magnetic path length(L) equal to the mean circumference, 50π mm?
If yes, then for question (c), should I skip it and go to question(d)&(e) to calculate (R) and (Fm), then only answer (c)?

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#### MrAl

Joined Jun 17, 2014
7,757
Hello,

The magnetic path length is taken to be the mean circumference if the cross sectional area is constant and the material is uniform throughout.

#### wayneh

Joined Sep 9, 2010
16,399
Agreed. Think of it as the average length of all the various field lines. I suppose for an irregular cross section it would be the area-weighted average length. So if most of the material is at the outer perimeter, the average field line would be longer than if most of the cross section is at the inner edge.