Question

Magnetic stored energy density for iron is given by ______

(a) 1/2 B/μ

(b) 1/2 B^2 μ

(c) 1/2 ∅^2 Rl

(d) 1/2 B^2/μ

I have been asked this question in homework.

This intriguing question comes from Singly Excited Magnetic Systems in portion Magnetic Circuits of Electrical Machines

Answer 1

Right option is (d) 1/2 B^2/μ

The explanation: Magnetic stored energy density for iron is given as

wfld=Wfld/((Length of the magnetic path through Iron)*(Iron area normal to the magnetic flux))=1/2  (F∅)/(length*Area)=1/2  F/length  ∅/area=1/2  H*B

Also, H = B/μ,thus wfld=1/2  B^2/μ.