B=ΦAandB=μH⟹H=Bμcap B equals the fraction with numerator cap phi and denominator cap A end-fraction space and space cap B equals mu cap H ⟹ cap H equals the fraction with numerator cap B and denominator mu end-fraction

(a) Total reluctance, (b) Flux (\Phi), (c) Compare flux with the no-gap case – why is it so much lower?

The sum of MMF drops around a closed loop equals the total applied MMF.

$$B = \frac\PhiA$$