# Mean Path Length of a Magnetic core????

#### Jas69

Joined Feb 17, 2017
5
Hello,

I am first year Electrical and Electronic engineering student. I have a question about the mean length of magnetic circuit. Are you guys active members on this chat ?

Thanks
Jas

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#### Jas69

Joined Feb 17, 2017
5
Hello,

I need help on this question which I have attached to this message. All I want to know is how did they find out the mean magnetic length (l) in this question?

#### Kermit2

Joined Feb 5, 2010
4,162
If you do some simple arithmetic and calculate the distance from the center point of each side to the opposite center point you find that you must subtract 1cm from each edge to be centered.
1 cm from each end is 2 cm.
8 cm minus 2 cm equals the center to center distance of a side.
There are four sides
4 times 6 cm is the mean path length. MINUS the length of the gap.

#### Jas69

Joined Feb 17, 2017
5
Hey thanks for replying so quickly.

I'm sorry I'm actually a really dumb student studying electrical and electronic engineering and I don't understand what you mean. I understand that there are 4 sides and that you multiply by 4 and then subtract 0.5 because of the air gap, but I do not understand how you they got 6cm. Would it be possible if you could show me with a diagram about what you are trying to say ?

Thank you.

#### Jas69

Joined Feb 17, 2017
5
If you do some simple arithmetic and calculate the distance from the center point of each side to the opposite center point you find that you must subtract 1cm from each edge to be centered.
1 cm from each end is 2 cm.
8 cm minus 2 cm equals the center to center distance of a side.
There are four sides
4 times 6 cm is the mean path length. MINUS the length of the gap.

Hey thanks for replying so quickly.

I'm sorry I'm actually a really dumb student studying electrical and electronic engineering and I don't understand what you mean. I understand that there are 4 sides and that you multiply by 4 and then subtract 0.5 because of the air gap, but I do not understand how you they got 6cm. Would it be possible if you could show me with a diagram about what you are trying to say ?

Thank you.

#### Kermit2

Joined Feb 5, 2010
4,162

#### wayneh

Joined Sep 9, 2010
17,168
A possible way to make this really hard – for an exam question, for instance – is to have an asymmetrically shaped core. The important thing for computing the mean path is that each path must be weighted into the mean by the cross sectional area corresponding to that path. You want the average path length averaged over the cross-sectional area. It's not just the average of the max an min path as you can get away with above. That simple approach works for symmetric cores, such as squares, rectangles and it's been proven for toroids as well.

#### Jas69

Joined Feb 17, 2017
5
OMG!! Thank you so much. Seriously thank you so much. ))

#### MrAl

Joined Jun 17, 2014
9,194
Hi,

If you have a metal core that has uniform cross section but also have an air gap, then the core magnetic path length is the mean length of the core with the air gap filled minus the air gap. The length of the air gap is then just the length of the air gap.
So you actually have two lengths here: the core metal mean length and the air gap length. You need to have both of those to do anything with the construction.