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Problem with Ampere's law

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  1. Jul 16, 2015 #1
    hello everybody!
    I have a problem with ampere's low.assume that we have an iron core with a winding in on side of it as sketched in the below image.we want to find H(magnetic field strength) and B(magnetic flux density) in the core in different condition shown in the right of image .the cross-section area of the core is constant in every points and we don't want to ignore core reluctance.in all of the conditions,the ampere loop, winding turns and the current pass through the conductor is constant. according to ampere's low, H must be equal in all of these conditions.but,simulations have different result and H change in each of the conditions.intuitively,the H should be different because of changing in the distance of winding from core.so,why ampere's low can't show the difference in H?
     

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  3. Jul 16, 2015 #2

    DEvens

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    Maybe I twill help if you write down Ampere's law. Then you can notice that it isn't just "H must be equal" but rather it is an equation. And the equation has various parts. And those parts relate to the things that are changing in the different cases.
     
  4. Jul 16, 2015 #3
    the ampere's low says:integration of dot product of H in l(where l is the unit vector of ampere loop that is tangent to path)over a closed loop will be equal to N*I.here ,we can assume that the angle between l and H in all of the points of ampere loop(shown in the image) is zero, so dot product converted to numeric product and we can say:the integration of (H magnitude)*(l) is equal to N*I.we neglect flux leakage(and the area of cross-section doesn't change ),so the magnitude of B and H is equal in each point of the core.and eventually the magnitude of H depends on N,I and l.in the above conditions all of these variables is equal so according to ampere's low H must be equal in all cases.(but it doesn't in fact)
     
  5. Jul 16, 2015 #4

    DEvens

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    Law. It is Ampere's Law.

    https://en.wikipedia.org/wiki/Ampère's_circuital_law

    I suspect that English may not be your first language. I apologize if that is the case. If I had to work in any language besides English I'm pretty sure I'd starve. But it's hard to look this stuff up if you don't spell it correctly.

    So you seem to have a contradiction. What did you forget?

    Are B and H really "equal in each point of the core"? How are B and H related?
     
  6. Jul 16, 2015 #5
    Ampere's Law.I am really sorry for my mistake,but It is better to focus on the context of passage instead of its spelling problems(it is clear that I made mistake).I have read your mentioned page before writing this thread.yes,you are right. "and H" was superfluous,but you could understand it from the next sentences.the correct sentence is:"the magnitude of B equal in each point of the core".I'm sorry for my English,but please read my posts patiently and think about it and then answer to it!Thank you
     
    Last edited: Jul 16, 2015
  7. Jul 17, 2015 #6

    DEvens

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    Pretty sure I did answer your question. I said: So you have a contradiction. What did you forget?

    What changes between your cases? Does the thing that changes appear anywhere in Ampere's Law?
     
  8. Jul 17, 2015 #7

    davenn

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    and also, how about putting spaces after your full stops and commas.... would make it a heck of a lot easier to read and understand than all your sentences just running together in one continuous stream of words

    learn something new and make it easier for people to help you :smile:

    Dave
     
    Last edited: Jul 17, 2015
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