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Magnetic powder in a solenoid - how would it react?

  1. May 12, 2015 #1
    Suppose I have a plastic tube about 70% full with magnetic powder, with a copper coil solenoid around the cylinder.
    By "magnetic powder" I mean each particle is actually a tiny permanent magnet with its own magnetic field. - like you can see in this video
    When there is no externally applied magnetic field, the particles of the powder do their best to clump together and find north and south poles to complete their magnetic circuit.
    What happens when we turn on the solenoid? How would the magnetic powder react? Would the orientation of resulting magnetic field resemble that of a standard iron core electromagnet? (like the one shown here - http://www.pirate4x4.com/tech/billavista/Wiring/Part2/images/elmag_400.jpg )
    Would the magnetic field of the powder interfere with the field in the current carrying copper?
    Last edited: May 12, 2015
  2. jcsd
  3. May 12, 2015 #2


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    Gold Member

    Assuming that you are only filling the tube 5% :

    Microscopically the powder will form theads ( or rather thin chains ) parallel to the tube.

    Macroscopically these chains will take a form like an ear trumpet at the ends of the tube.

    The powder magnets will always try to find some space in the neighbourhood, arranging themselves so that they will destroy ( eliminate ) the magnetic energy.

    You say:
    but I don't like this formulation: North and south poles are nothing ( but an educationally approach ). They are not "small particles" concentrated e.g. at each end of a permanent solenoid magnet. They are just a surface that is crossed by a magnetic field, where the permeabilities on each side of the surface are different. You cannot saw through a magnet and hold the north pole in your hand. You will just create a new surface that becomes a "south pole" ( out of nowhere ).
    Last edited: May 12, 2015
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