| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
25 Nov 2005 10:11:30 PM |
| Object: |
How to measure H (magnetic field strength)? |
Hi, I have a question and would appreciate any help:
The force on a moving electric charge is defined in terms of the
magnetic flux density B, thus B can be measured. B=mu_o(H+M). Is there
any way to physically measure H? If you remove the original B source,
and then use a Hall probe, the resulting value will be M, and knowing B
you can calculate H. But in the presence of a material with
non-negligible mu, can you actually physically measure H, and how so?
You must be able to physically measure H somehow, otherwise how would a
hysteresis curve be plotted? Or are hysteresis curves only made with
electromagnets, and with an electromagnet you can easily calculate H
due to the current, and thus avoid having to measure it.
Say I have a piece of steel in air, and apply a strong permanent magnet
to one side of it so that most of the flux from the permanent magnet
travels through the steel. Then on the other side of the piece of steel
(where there is no permanent magnet) I take a Hall probe and place it
very closely to the steel and orient it so that it measures the
tangential component comming out of the steel. Now what i'm measuring
on the side of the steel with the Hall probe in the air is about H,
since air has a negligible mu value. Since the tangential components of
H at the steel air boundary are equal so the value of H i measure in
air, should be about equal to the value of H in the steel. Is this
correct, would this be a method of finding the value of H in the steel
in this situation?
Thanks.
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| User: "Androcles" |
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| Title: Re: How to measure H (magnetic field strength)? |
26 Nov 2005 12:13:37 AM |
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<muknot@gmail.com> wrote in message
news:1132978290.108693.73060@f14g2000cwb.googlegroups.com...
Hi, I have a question and would appreciate any help:
The force on a moving electric charge is defined in terms of the
magnetic flux density B, thus B can be measured. B=mu_o(H+M). Is there
any way to physically measure H? If you remove the original B source,
and then use a Hall probe, the resulting value will be M, and knowing B
you can calculate H. But in the presence of a material with
non-negligible mu, can you actually physically measure H, and how so?
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/experiment/lab/expt3/expt3.html http://engr.astate.edu/jdg/Circuits/Lab/12RLC-ResonantCircuit.html http://www.intuitor.com/resonance/circuits.html http://www.du.edu/~etuttle/electron/elect20.htm http://www.du.edu/~etuttle/electron/elect34.htm http://www.ndt-ed.org/EducationResources/CommunityCollege/EddyCurrents/Physics/mutualinductance.htmhttp://www.faqs.org/docs/electric/AC/AC_12.htmlStart measuring. :o)Androcles> You must be able to physically measure H somehow, otherwise how would a> hysteresis curve be plotted? Or are hysteresis curves only made with> electromagnets, and with an electromagnet you can easily calculate H> due to the current, and thus avoid having to measure it.>> Say I have a piece of steel in air, and apply a strong permanent magnet> to one side of it so that most of the flux from the permanent magnet> travels through the steel. Then on the other side of the piece of steel> (where there is no permanent magnet) I take a Hall probe and place it> very closely to the steel and orient it so that it measures the> tangential component comming out of the steel. Now what i'm measuring> on the side of the steel with the Hall probe in the air is about H,> since air has a negligible mu value. Since the tangential components of> H at the steel air boundary are equal so the value of H i measure in> air, should be about equal to the value of H in the steel. Is this> correct, would this be a method of finding the value of H in the steel> in this situation?>>> Thanks.>
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| User: "jpolasek" |
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| Title: Re: How to measure H (magnetic field strength)? |
26 Nov 2005 08:11:57 PM |
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H is not magnetic field strength, B is. H is the forcing function which
you can specify ND DESIGN as so many amp turns per meter. You are not
specific enough how you get your B, or what your setup is, but you get
B from something you can specify: H.
Only God knows what B will result since it would ordinarily require
solution of insoluble partial differential equations with god-awful
boundary conditions. In the farfield of space the answer is easier. Be
sure you use SI equations or you'll never know what's going on. You
appear to appreciate the difference between B and H.
John Polasek
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