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Magnetic forces

  1. Jul 28, 2005 #1
    In giving directions of magnetic forces, we sometimes use the term "out of paper" or upwards, but what really is the difference between them?
     
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  3. Jul 28, 2005 #2

    quasar987

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    upward lies in the plane of the paper while "out of paper" is perpendicular to it.
     
  4. Jul 28, 2005 #3

    mukundpa

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    Perpendicular to the paper?? What do you thinK about normal?
     
  5. Jul 29, 2005 #4
    If there's just a wire placing horizontally, how can you determine whether the force lies in the plane or out of the plane?
     
  6. Jul 29, 2005 #5

    mukundpa

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    That will depend on direction of magnetic field and that of current. Use Fleming's left hend rule.
     
  7. Jul 29, 2005 #6

    quasar987

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    perpendicular and normal are synonim
     
  8. Jul 29, 2005 #7

    mukundpa

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    but I think that perpendicular is to a line and normal is to a plane.
     
  9. Jul 29, 2005 #8

    quasar987

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    After a bit of research, I think both terms are good here.

    Mathworld says for the definition of 'normal vector':

    "The normal vector, often simply called the "normal," to a surface is a vector perpendicular to it."

    So it makes sense to talk about a vector perpendicular to a surface (we knew that of course).

    'Normal' is just a more sophisticated way of saying the same thing.

    And it doesn't seem right to say that 'normal' and 'perpendicular' are synonim, because the term normal, as I understand it, can only be used when talking about a vector. So we can say that two planes are perpendicular to one another, but we cannot say that they are normal to one another.

    sources:
    http://mathworld.wolfram.com/NormalVector.html
    http://mathworld.wolfram.com/Perpendicular.html
    http://en.wikipedia.org/wiki/Surface_normal
     
    Last edited: Jul 29, 2005
  10. Jul 30, 2005 #9

    mukundpa

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    So will it be correct to say that two vectors are normal to each other if angle between them is 90.
     
  11. Jul 30, 2005 #10

    quasar987

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    I would say 'no'. 'Normal' is only used to describe perpendicularity of a vector wrt a plane.

    Have you seen this used in a textbook before? I think they mostly use the term 'orthogonal', which is a synomim to perpendicular when talking about simple object such as lines, vectors, planes, etc., but actually extend to more abstract mathematical objects as the generalisation of the notion of perpendicularity.


    See https://www.physicsforums.com/showthread.php?t=81294&highlight=orthogonal
     
    Last edited: Jul 30, 2005
  12. Jul 30, 2005 #11

    mukundpa

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    Thanks for your valuable explainations.
     
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