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Magnetic lines

  1. Nov 13, 2009 #1

    A question which arises to me is about magnetic fields of a wire or a permanent magnet,
    Are they continuous? or are discontinuous like what we draw them when We want to show them in a paper? If they are continuous then why we see discontinuous lines when we make a test by iron's particles?
    Are they real LINES of filed or are just Continuous Fileds?

    Thanks a bunch.
  2. jcsd
  3. Nov 13, 2009 #2


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    Staff: Mentor

    A magnetic field is continuous in the sense that it exists (has a magnitude and direction) at every point in space. Are you familiar with vectors and using arrows to represent them? The most complete graphical representation of a vector field such as a magnetic field is to attach an arrow to every point in space, that represents the magnitude and direction of the field at that point. But with an infinite number of points, that makes a messy diagram that's hard to read, so we usually use a sampling of points. I can't find an actual magnetic field map that uses this idea right now, but here's a wind speed map that uses the same idea. Concentrate on the arrows:


    That's because iron filings act like little magnets in this situation, so they tend to stick together, and form clumps.
  4. Nov 13, 2009 #3
    Field lines are imaginary constructs only,they do not actually exist.Having said that they are very useful constructs particularly from a practical point of view.The lines are continuous. For an isolated permanent magnet or current carrying conductor the closer lines form closed loops joining the poles.More distant lines may link with other magnetic materials which themselves contributes to the resultant field pattern.It is believed that the field goes on forever but weakens with distance.The size of the paper and other factors put limitation on the field pattern you are able to observe.
  5. Nov 13, 2009 #4
    A major difference between magnetic field lines and electric field lines is that magnetic field lines are always continuous, and never abruptly change magnitude (for B (Tesla)). Electric field lines usually terminate on conductors (except when generated by magnetic fields), where there are charges (electric monopoles). There no (yet found) magnetic monopoles.
    Bob S.
  6. Nov 18, 2009 #5
    Thanks, so they are continous but we just show them as lines.
    I have a big problem undersatnding these:
    field lines!
    Density of flux, density of field?
    and specially flux!
  7. Nov 18, 2009 #6
    For starting out, thinking of magnetic lines of flux as continuous is fine....but there are more funadamental questions about whether anything is really "continuous" or actually discrete at the tiniest of scales....

    You might also ask are things analog or digital? I don't believe anyone knows for sure. But Einstein's relativity is continuous and works well for large scale activities; quantum mechanics is discrete and works better at the tiniest of scales.

    Here is one discussion:

    and here is another:
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