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Can someone explain the iron shavings flux line experiment to me?

  1. Dec 19, 2013 #1
    In regards to the famous experiment where a magnet is put under a sheet of paper with iron shavings on top, i dont understand why they distribute according to the shape of the magnetic lines of flux. (as seen in the link below)

    https://www.google.ca/search?q=iron+shavings+magnetic+field&source=lnms&tbm=isch&sa=X&ei=QIuyUuevHubmyQHKhYCgCg&sqi=2&ved=0CAcQ_AUoAQ&biw=1454&bih=738

    I'll explain the way im thinking of it so someone can correct me.

    I imagine a magnet as giving off a fixed vector force in all directions, and that the magnitude and direction of the vector at any point is dependent on proximity to the negative/positive poles.

    So when you dump the iron shavings over the magnet, i dont understand what causes them to gravitate to these specific lines, and why there would be gaps without shavings between the flux lines.

    I imagine the distribution of the iron shavings to be relative to the magnetic vector frce applied to them from where they land.
     
  2. jcsd
  3. Dec 19, 2013 #2

    Philip Wood

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    Gold Member

    It's quite complicated… The magnetic domains in the filings are dragged partly into line by the magnet's field, making the filings themselves into temporary magnets. Each then experiences a torque tending to align it with its long axis parallel to the field. If the field is very non-uniform, as near the poles of the magnet, the filing will experience a net force towards where the field is strongest, so the magnet's poles tend to get coated with filings - especially if you tap the paper on which the filings are resting. There will also be forces between the (magnetised) filings themselves, tending to make them concatenate into lines.

    This answer is quick and misses out a lot. Perhaps its may have some use as a starting point.
     
    Last edited: Dec 20, 2013
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