 Magnetic Circuits

Section 9.7 of Electromagnetic Fields and Energy by Hermann A. Haus and James R. Melcher. Whole-book authorship applies. web.mit.edu/6.013_book/www/chapter9/9.7.html. Example 9.7.1 explicitly assumes a gap small compared with transverse dimensions and approximately uniform fields in circuit sections. The subsequent discussion distinguishes those estimates from a full magnetic scalar-potential solution.