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Calculate movement of steel in magnetic field

  1. May 19, 2015 #1

    A steel plate with dimensions a * b and thickness t is moving in a magnetic field of stationary permanent magnet. the movement of steel plate is parallel to the magnet field. One pole of the magnet is perpendicular to the axis of steel movement. what force will be required to move this steel plate in the magnetic field 'B'. let he distance between the magnet and steel be 'd'

  2. jcsd
  3. May 19, 2015 #2


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    Staff: Mentor

    Welcome to the PF.

    Is this for schoolwork? What is the context of the question?
  4. May 19, 2015 #3


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    Science Advisor

    What kind of steel? Different alloys have different magnetization properties. SS 304 is pretty much nonmagnetic.
  5. May 20, 2015 #4
    Low carbon steel. it has very good magnetic property.
    I want to analyse the force required to move a steel plate in magnetic field for a project.
  6. May 20, 2015 #5


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    Take a look at this

    You will need to know the magnetic field strength B at a distance from your magnet. If your metal plate is small compared to the distance to the magnet, then maybe you can approximate B as constant across the metal. Otherwise, it will get more complicated. Anyways, you might be able to get a gross estimate by assuming B is constant.

    You need to know the permeability of the steel. This can vary a lot between alloys and tempering. http://en.wikipedia.org/wiki/Permeability_(electromagnetism) has a table of some permeability values of some materials. You see "Ferritic stainless steel (annealed)" is given as 1000-1800.

    Then you can calculate the force on the metal, which will tell you the acceleration of it.
  7. May 26, 2015 #6

    thanks for your reply.
    the link has to do with electromagnets and the problem is very different.
    i know the magnetic field strength B. the steel is fairly bigger than the permanent magnet.
    there are two cases here.

    case1. steel is stationary at a distance d from the pole of magnet. i know the force with which the steel is pulled by magnet acting Normaly.
    steel can be moved in two directions.
    one, the steel is moved away from the magnet perpendiculary
    or , steel is moved horizontally.

    how to calculate the force acting on steel when it is moved
  8. May 26, 2015 #7
    I'd put the problem differently.
    A permanent magnet of known dimension and magnetic field strength B is fixed. A steel plate of known dimension and thickness and permeability is placed at a distance d, such that the pole of the PM faces the flat surface of steel. The force acting due to PM on steel is known.
    Now, if the steel plate is moved horizontally, i.e. parallel to the pole, then i'd like to calculate the force required to move the steel plate, ignoring friction.
  9. May 26, 2015 #8


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    If the steel is moving much slower than the speed of light and the steel is not charged, I don't think the motion of the plate will make any difference to the force.
  10. May 27, 2015 #9
    thanks for your anwer

    suppose the force on steel due to magnet kept below it at a distance of 1 cm is 20 N. and if this steel is moved horizontally just to be outside its magnetic field, then the force required, to move it disregarding friction, should be atleast 20 N.
    But it is observed that moving steel horizontally takes less force but towards the edge compared to moving it up along the axis.
    i have seen some links that say the energy gets distributed while moving steel parallel to the magnet, but there is no formula to support this.
    can you share some details on this

  11. May 27, 2015 #10


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    Hmm, I guess I missed an effect in my last post. If the steel is moving through a changing magnetic field, then there will be eddy currents formed in the steel which create some resistance to the motion. There will be more resistance in directions that change the magnetic field more.
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