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Magnetic forces

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In giving directions of magnetic forces, we sometimes use the term "out of paper" or upwards, but what really is the difference between them?
 

quasar987

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upward lies in the plane of the paper while "out of paper" is perpendicular to it.
 

mukundpa

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

mukundpa

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That will depend on direction of magnetic field and that of current. Use Fleming's left hend rule.
 

quasar987

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perpendicular and normal are synonim
 

mukundpa

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but I think that perpendicular is to a line and normal is to a plane.
 

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
 
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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.
 

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
 
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mukundpa

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Thanks for your valuable explainations.
 

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