Conventions for Magnetic Quantities in SI

Abstract

Magnetic equations written in International Standard (SI) units usually use either the Sommerfeld convention (m = IA, H = B/μ0−M) or the Kennelly convention [m′ = μ0IA, H = 1/μ0(B−M′)]. An alternative is the “SI electric” convention (m = IA, H = B−μ0M) proposed by Stopes-Roe. In this paper it is shown that the “SI electric” convention arises naturally from the comparison of pole and current loop models for magnetic materials, and hence overcomes the problems of illogical factors of μ0 inherent in the Sommerfeld and Kennelly formulations. This approach clarifies the roles of the field vectors B and H.