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Simple fundemental Electromagnetics question

  1. Mar 27, 2014 #1
    I'm just trying to get my head around electromagnetics for the first time, and need help understanding a question that asks:

    "Using BH curves find the maximum permeability of the cast iron forming the magnetic path."

    Now from wikipedia I know that the permeability of cast iron should be around 0.25H/m.

    What I don't understand is how to get this quantity from a B-H curve like this one:
    http://imgur.com/eiv6IuN

    Now what I do understand is that permeability is given by B/H essentially. That would imply it is the gradient of these lines.

    So to find the maximum permeability all we need to d is find the point with the most positive gradient.

    Is this logical correct?
     
  2. jcsd
  3. Mar 27, 2014 #2

    rude man

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    It depends on what permeability you have in mind.

    For small perturbations about an operating point H, the slope of the B-H curve is the permeability. In other words, dB/dH. It would be called dynamic permeability.

    But one can also talk of static permeability. To get it, you again pick your operating point H along the B-H curve but now permeability is simply B/H.

    In both cases the hysteresis curves show that the B corresponding to your picked H depends on the history of applied H.

    I'm sorry, your image does not show on my computer.
     
  4. Mar 27, 2014 #3

    NascentOxygen

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    The image referred to by Learnphysics ...

    eiv6IuN.png
     
  5. Mar 27, 2014 #4

    rude man

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    Thanks Nascent. As i suspected, those are not hysteresis curves, avoiding the ambiguity I referred to as 'history'.

    so my first comment applies except ignore the bit about history.

    @nascent - any idea why my pc didn't show the image?
     
  6. Mar 27, 2014 #5

    NascentOxygen

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    Yes, poster cited as an image a URL which is not an image file. Incorrect use of
     
  7. Mar 27, 2014 #6

    rude man

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  8. Mar 27, 2014 #7

    NascentOxygen

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    I found OP's URL and fed it to the browser, and copied the URL of the image that came up.
     
  9. Mar 27, 2014 #8

    rude man

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    Thanks!
    rm
     
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