# magnetic circuit question

#### Jaafar Ali

Joined Dec 3, 2016
1
Hi,
I was wondering whether anyone could help with this question:

For an iron ring of rectangular cross-section with mean radius R, radial thickness 2r and height t: (a) derive an expression for the permeance P of the iron ring, and (b) obtain an expression for the approximate permeance Pʹ of the ring if R>>r.

Thanks a lot, any help is appreciated.

#### wayneh

Joined Sep 9, 2010
16,398
You can treat a ring as straight piece using the mean circumference as the length.

#### MrAl

Joined Jun 17, 2014
7,656
Hi,
I was wondering whether anyone could help with this question:

For an iron ring of rectangular cross-section with mean radius R, radial thickness 2r and height t: (a) derive an expression for the permeance P of the iron ring, and (b) obtain an expression for the approximate permeance Pʹ of the ring if R>>r.

Thanks a lot, any help is appreciated.
Hello,

Were you given a value to use for the permeability of iron?
That can vary quite a bit. If you were given a value then you can just use a small formula which includes the cross sectional area and mean magnetic path length.
If not, then maybe just call it 'mu' (Greek letter mu).

#### Kermit2

Joined Feb 5, 2010
4,162