# Homework Help: Total reluctance in a magnetic core

1. Jul 22, 2012

### kevinb

1. The problem statement, all variables and given/known data
I am looking for a general explanation of when the total reluctance of a magnetic circuit is not equivalent to the sum of the reluctances if each area. In several examples the text has added 2 areas in parallel and then added the third area. I'm not 100% sure on when this is required.

2. Relevant equations

I use R=l/(μA) to determine the reluctance of each area, but don't know if/when reluctances need to be added in parallel.

3. The attempt at a solution

For example, if I have a shape like this: where the shaded region is air and the rest (the white area) is iron, I calculated the reluctance for the left, middle, right and small air gap. However, is the total the simple addition of them or are the left and right "legs" in parallel?

Last edited: Jul 22, 2012
2. Jul 22, 2012

### Astronuc

Staff Emeritus
The center is in series with the two outer loops which are in parallel.

See page 11 of 35 in http://www.ece.msstate.edu/~donohoe/ece3183magnetic_circuits_and_transformers.pdf [Broken]

or page 29 of 33 in http://www1.mmu.edu.my/~wslim/lecture_notes/Chapter4.pdf [Broken]

It's a fairly standard magnetic circuit. One must treat the air gap as well.

Last edited by a moderator: May 6, 2017
3. Jul 22, 2012

### kevinb

Thank you very much. Those two documents were perfect explanations for this particular circuit, but I'll read them further so I gain a better grasp of the general principles as well.