# Calculating reluctance in this circular shape?

#### MaxMeyer

Joined Oct 26, 2020
6
I do not quite understand how to calculate the resistance.

#### MrAl

Joined Jun 17, 2014
8,866
I tried to solve this question but I don't know how the reluctances are the different? (since we have the same width in all of the shape) what are the other factors that affect the reluctance value in the overall shape?

View attachment 220505
Hello,

In this section you are supposed to show your best attempt to solve it yourself first.
And in your post what reluctances are you saying are "different"? You should show those as well as how you tried to calculate it already.

#### Papabravo

Joined Feb 24, 2006
18,093
Just as there is a relationship called Ohm's Law for DC circuits with resistors, the problem statement suggests there is an isomorphic (same form) law that relates reluctance and two other quantities, and this law follows the same procedure as a DC circuit with resistors when there are series and parallel structures. So you have the length of the magnetic circuit and the cross sectional area of the magnetic circuit, and they give you the dimensionlessμ quantity μr. All you need is the value of μ0 and the rest should be easy.

Hint:
μ0 is the permeability of vacuum, equal to $$4\pi \; \times\;10^{-7}\; \frac{\text henry}{\text meter}$$

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