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Magnetic field lines

  1. Aug 22, 2010 #1
    I have seen people write that there are no such things as "field lines", but that the magnetic field is a continuum. But
    iron filings on a paper over a magnet will arrange on lines of the magnet's field....Is this an illusion, or are there "lines" that make up the field?...thank you
  2. jcsd
  3. Aug 22, 2010 #2
    There are no lines.

    If you see icicles hanging from a roof in winter, You could say these grow 'along lines of gravity'.

    Same thing.
  4. Aug 22, 2010 #3
    thanks, so it is an illusion, created by the properties of magnetized iron filings ...
  5. Aug 22, 2010 #4


    Staff: Mentor

    I really like this analogy!
  6. Aug 22, 2010 #5
    I could be wrong on this, but isn't the term 'field lines' a mathematical construct to define the interaction and area between the two bodies? and this leads to confusion when it's miss-used to simplify the explanation.

    if it was a constant fixed field than it would exhibit influence over anything that was in the field, right? but if it's the field arising from the interaction between magnetic bodies then the field would be proportional to the force of those bodies. If I'm wrong let me know.
  7. Aug 22, 2010 #6
    Field lines do exist, but they are no more than a form of countour line.

    You can draw equipotential, equidirectional, equigradient lines in a field or continuum. All that means is the property of interest does not vary when moving along the line.

    What it does not mean is that there is some sort of 'string' pulling our test piece along such a line.
  8. Aug 22, 2010 #7
    Think of the lines like contour lines on a topographical map. There is no correct number of lines to draw. In fact, there are an infinite number of lines one could draw. What is important is that they communicate the proper relationship between one place and another. Where the magnetic field is stronger there are "more" lines. This is analogues to contour lines, where the mountain is steeper there are more lines. How many you have depends on the scale you choose.
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