# Length of magnetic path?

Discussion in 'Electronic Design' started by amdx, Oct 27, 2006.

1. ### amdxGuest

I find the formula for the Reluctance of an air core solenoid as;

Reluctance = (length / cross-section) x (1/mu)

In the description length is just the length of the solenoid.
Why wouldn't the length be equal to
2 x the length plus some distance around both ends?
This would seem to be the distance the lines of flux travel.

Mike

2. ### Bob EldGuest

This assumes an infinitely long coil where the length is normalized unity
length or some other convienient number that is a small fraction of the
total. Per meter or per cm is usual. Indeed, in a short coil with defined
ends, the path is much more complicated and there are emperical formulas to
deal with it.

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