A ferrite fridge magnet is a thin disc of diameter and thickness
PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Magnetostatics · Magnetic materials
Electricity, Magnetism and Electromagnetism, Ch Magnetisation, bound currents and the auxiliary field H
Problem
A ferrite fridge magnet is a thin disc of diameter 30mm and thickness 3.0mm, magnetised uniformly across its flat faces with M=1.4×105Am−1. There is no free current anywhere. For the shapes quoted in this chapter, the interior auxiliary field of a uniformly magnetised body is: in a thin disc magnetised across its faces, H close to −M; in a long thin needle magnetised along its length, H close to zero.
((a)) Predict the magnitude of H inside the disc and state its direction relative to M and relative to the disc's north face.
((b)) Hence predict the magnitude of B inside the disc.
((c)) A needle of the same ferrite, magnetised along its length to the same M, is compared with the disc. Predict the magnitude of B deep inside the needle.