Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: djc0245 on 07/06/2008 18:22:53

Title: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: djc0245 on 07/06/2008 18:22:53

Principle:    When using a coil for induction of a longitudinal magnetic field, the appropriate field strength selection is based upon the following formula:

                       I - Amperes required
     KD               K - 45,000 amperes turns
I = ----              L - Length of specimen
     NL               D - Diameter of Specimen (if solid)
                       N - Number of turns/wraps in coil

Effective area:   18 inches, 9 in. from center of coil/wrap both directions.
Given results:    Polarization of aligned electrons in specimen, N at one end, S at the opposite end.
Verified by:      Flux field leakage, demonstrated by lines of force at each end of specimen.

Inquiry:  Due to the lack of uniformity in most specimens' perimeter profile, Isn't there an existence of a neutrality point (maybe very narrow - almost indiscernible) in the center of the coil between the poles? Since a measurable reduction of applied field strength exists there? And shouldn't there be an established theoretical or industrial standard of identifying the neutral point, as a "Dead Zone"? Or for validity, at the least establish the practice of repositioning specimens?

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Title: Re: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: Bored chemist on 08/06/2008 14:11:48

Good question and I don't know the answer.
But I strongly advise you to remove your email address before it gets spammed to death.

Title: Re: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: lyner on 08/06/2008 22:13:43

The actual system description is a bit vague and I can't be sure what the actual question is  but my answer to the question as I understand it is:
I don't think there is any likelihood of a 'neutral point' (do you mean 'null')
The field might be a bit non-uniform along the axis of the coil due to  the finite spacing between the turns  but Ampere's Law, I think, precludes having nulls .
Perhaps a diagram would help to make the question more clear.

Title: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: Soul Surfer on 11/06/2008 08:10:51

No.  The magnetic field runs substantially uniformly along the axis of the coil.  outside the coil the field loops back substantially like a bar magnet.  Magnetic "poles" in this context are rather ill defined areas in the vicinity of the ends of the coil.

Title: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: daveshorts on 11/06/2008 09:17:52

A field line is the route that an unnattached N pole with no mass would follow, so it would go straight from the North end of the coil to the south end very rapidly.

[diagram=353_0]

But if you had two North poles near each other then there would be a 'dead zone' of no field between them.

Title: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: Atomic-S on 13/06/2008 04:41:16

The field inside a coil is nowhere zero.

Title: Is there a magnetic "dead zone" somewhere between the two poles of a coil?
Post by: qazibasit on 13/06/2008 13:39:54

good numerical and a real nice effort.