Sign up ×  This is a past exam question from one of our
lectures, and we have an issue with (i), I believe I need to use
the equation $\rho=\frac{RA}{l}$, but I am not sure - could
someone enlighten me on the issue?  A mild steel ring of
magnetic permeability 380, having a cross sectional area of
$500mm^2$ and a mean circumference of $400mm$, has a coil of
$200$ turns wound uniformly around it.  Given that the magnetic
permeability of free space is $400 nH/m$ determine:    • (i) The
reluctance of the ring.    • (ii) The current required to
produce a flux of $800\mu$ Wb in the ring.  share|cite|improve
this question The equation above has nothing to do with the
problem below. In case the problem would be in SI units, I might
be able to solve it... :/ –  Pygmalion May 7 '12 at 17:03 That
figure for magnetic permeability of free space doesn't seem to
be right. –  Mark Beadles May 7 '12 at 19:19 I was puzzled by
N=200 in the numerator and I found it was NOT necessary. Please
check for the explanation. –  user3496