Magnetic pole

  • Thread starter ascky
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I started reading Lectures on Electrical Engineering Vol I, Steinmetz. I thought I should be able to understand most of it, but I don't get the first page! It says that: 'The total number of lines of force issuing from a magnet pole is called its magnetic flux. The magnetic flux, phi, of a magnet pole of strength m is, phi = 4*pi*m '.

What does this mean, and what are the units of m? I thought that because the magnetic lines always formed closed circuits that the flux through a closed surface around a magnetic pole should be zero. I'd really appreciate it if someone could explain this to me.
 

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  • #2
Meir Achuz
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ascky said:
I started reading Lectures on Electrical Engineering Vol I, Steinmetz. I thought I should be able to understand most of it, but I don't get the first page! It says that: 'The total number of lines of force issuing from a magnet pole is called its magnetic flux. The magnetic flux, phi, of a magnet pole of strength m is, phi = 4*pi*m '.

What does this mean, and what are the units of m? I thought that because the magnetic lines always formed closed circuits that the flux through a closed surface around a magnetic pole should be zero. I'd really appreciate it if someone could explain this to me.
If a magnetic pole existed, the equations for a pole of strength m would by much like those for a charge q.
1. "Magnetic flux" here means [tex]\oint{\bf B\cdot dS}[/tex].
2. Just like Gauss's law, [tex]\oint{\bf B\cdot dS}=4\pi m[/tex],
in Gaussian units.
3. In Gaussian units, the units of m would be gauss-cm^2.
In SI units, I think it would be Webers (Whoever he was).
3. "I thought that because the magnetic lines always formed closed circuits...". That is only in the absence of a magnetic monopole.
With magpoles, magnetostatics becomes just like electrostatics.
I suspect your text is using one end of a long bar magnet as an abstraction for a magnetic pole, and not including the B inside the magnet
in finding the flux of 4\pi m.
 
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vanesch
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Yes, it seems that this book starts off really badly...
 

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