A problem on electromagmetism.

Discussion in 'Homework Help' started by Kihaule, Dec 28, 2012.

  1. Kihaule

    Thread Starter New Member

    Dec 28, 2012
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    It's my hope to receive a solution for this problem at most in 72 hours.
    Thanks in advance!
     
  2. vk6zgo

    Active Member

    Jul 21, 2012
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    Perhaps you should use that 72 hours on revision,so that you can solve it yourself.
    All that you need should be in your textbooks,or if not there,in your University/Tech School Library.
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    This is the standard stuff for making and inductor. There should be thousands of sites with basic formulae for calculating inductance, flux density, etc.

    Here's why you should learn how to do this and why flux density is critical: in the real world you will make inductors and transformers for applications where you know the current requirement and you have to pick the core type and size to make the inductor/transformer. For example: a ferrite core saturates at about 3000 gauss, so you would need to make the core large enough (and with correct number of turns) to give you the inductance you need without letting the flux density get so high that it saturates the core.

    Go forth and search, you will learn something important.

    http://en.wikipedia.org/wiki/Magnetic_flux


    http://www.ehow.com/how_6695344_calculate-flux-density.html


    http://www.mceproducts.com/knowledge-base/calc/calc.asp
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Well, if you want to solve it in less than 72 hours and you want help from here, then let's not waste a bunch of time trying to get you to show your attempt at a solution -- please just post your efforts to this point and, if possible, some specific thoughts or questions regarding specific points that you are unsure of or that seem to be keeping you from making further progress.
     
  5. Kihaule

    Thread Starter New Member

    Dec 28, 2012
    6
    1
    vK6zgo;
    Thank you for your challenge, more than 24 hours are already gone and so we've less than 48 hours. I've already done plenty of research on this question before I posted it here. Can you join your effort to find its solution?

    bountyhunter;
    Thanks for your references, though they were not much of a help but I appreciate your concern.

    wBahn;
    The main problem is how determine the values of flux (Φ), flux density (B) and field intensity (H) according to the following formulas

    first I have to find "H" from the following relation
    H = NI/l but it's still not clear to me on how I can determine the value of mean length "l" from the given figure.

    Next; I have to determine "B" from the following relation
    B = µ0µrH, but since I was unable to determine the value of H, I couldn't find the value of B. Similarly, I couldn't obtain the value of Φ from the relation
    Φ = BA, since I couldn't determine the values of both "A" and "B".
     
    Last edited: Dec 29, 2012
  6. WBahn

    Moderator

    Mar 31, 2012
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    Are you sure there isn't any other information given for the problem?
     
  7. Kihaule

    Thread Starter New Member

    Dec 28, 2012
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    Yeah, there isn't any other clue given!
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Last edited: Dec 30, 2012
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You have a solid continuous core. Draw the flux lines as they loop around the core. Now how long is the mean length?

    Hint: how long does each flux line travel?

    Double hint:

    Why do you suppose there are given dimensions for the height, length and width of the core?

    Triple hint:

    To calculate mean length you only need to know the linear distance the flux line goes.

    To calculate flux density, you must know the cross sectional area the flux lines pass through.
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    But without knowing the dimensions of the hole in the core, how can you determine the mean linear distance traversed by the flux?
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I think the complete dimensions need to be given. Since they are not, I assume the dimensions should be taken from the drawing.

    I would go back and ask the teacher on that.
     
  12. Kihaule

    Thread Starter New Member

    Dec 28, 2012
    6
    1
    Thanks for your assistance brethren! I really appreciate it. Keep it up.
     
  13. Kihaule

    Thread Starter New Member

    Dec 28, 2012
    6
    1
    Thank you for your assistance brethren! Unfortunately, the teacher isn't cooperative. I appreciate your concern, keep it up.
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    He'd be cooperative when I got done with him.
     
  15. WBahn

    Moderator

    Mar 31, 2012
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    How have you approach him (or her)? Try asking specific questions that demonstrate that you are making a concerted effort. For instance, you might try something like, "In order to calculate xxxxx, I need to determine the mean length traveled by the flux as it goes around the core. However, I think I need to know the dimensions of the hole in the core as well as the outside dimensions in order to do that. But the fact that they aren't given implies that they probably aren't required and that there must be another way, but I'm not seeing it. Could you confirm that the hole dimensions aren't needed and, if not, could you give me a bit of hint as to what direction I should be looking in?"
     
  16. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Also ask him how can somebody calculate flux density without being able to calculate the cross sectional area the flux is passing through.
     
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