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The translational force on a piece of iron in a magnetic field 
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#1
Feb913, 12:09 PM

P: 108

Ok so if there be a piece of iron in a uniform magnetc field B, what will be the force on the iron?
You can assume any variable you want, but i want to find the magnetic force that causes the iron pieces to move towards the magnet in terms of any variables, like it corsssectional area, length, position etc. 


#2
Feb913, 02:46 PM

Mentor
P: 11,917

The net force is 0. There might be a torque, depending on the orientation of the iron and its magnetic field (if present) and the external magnetic field.
You need a field which is not uniform to move magnets. 


#3
Feb913, 10:04 PM

P: 108




#4
Feb1013, 07:13 AM

Mentor
P: 11,917

The translational force on a piece of iron in a magnetic field
The iron bar will get a magnetic field similar to the external field, and this multiplied with the gradient of the external field should give some reasonable estimate for the force.
http://en.wikipedia.org/wiki/Force_between_magnets 


#5
Feb1113, 02:58 AM

P: 108

But then what to do? I need to find the developed pole strengths first, right? How do I do that? 


#6
Feb1113, 12:15 PM

Mentor
P: 11,917

A magnet does not consist of two separate poles. If you know the magnetic field (and assume it is the same everywhere in the magnet), it is fine.



#7
Feb1113, 09:19 PM

P: 108

Have I got a misconception about these things? Please help me. I am absolutely at a loss now! 


#8
Feb1213, 09:36 AM

Mentor
P: 11,917

I think it is a detour. It is possible, but you just multiply with things (like the volume) and divide by them again afterwards.



#9
Feb1213, 09:51 AM

P: 108

Ok... One more thing, does the developed pole strength at each end of the iron bar change with its position? I think the pole strength will keep varying as a function of the field the iron bar is in. Am I right?
By using the properties of the material, I got an equation for the pole strength. Its given by, s=χBA/μ , where χ is the susceptibility of iron, B is the field it is kept in, A is its crosssectional area and μ is the permeability of the surrounding medium. Is this correct? 


#10
Feb1213, 02:54 PM

Mentor
P: 11,917




#11
Feb1213, 09:50 PM

P: 108

I^{→}=M^{→}/V=M^{→}/A.l=s.l.M^{^}/Al=M^{^}s/A Then again, χ=I^{→}/H^{→}=I^{→}μ/B^{→}... and then the above expression of the pole strength 


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