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# Magnetic fields help watch

1. Why is it that in a uniform magnetic field moving the magnetic poles further apart causes the magnetic flux density to decrease? Surely the number of field lines per unit area remains the same?

Thanks
2. (Original post by krisshP)
Why is it that in a uniform magnetic field moving the magnetic poles further apart causes the magnetic flux density to decrease? Surely the number of field lines per unit area remains the same?

Thanks
Generally the field between two poles isn't uniform. If the field is strong and the poles are close together you get a pretty reasonable uniform field. That shows up as straight lines of flux.
But the lines of flux coming out of magnetic poles are not straight, and as you move the poles further apart, more of the lines go off to the side and fewer directly between the poles.

Common sense should tell you that as the poles move further away, the field gets weaker. If they are moved to infinity the field is zero. The flux density is a measure of how strong the field is. So how can this remain constant as you separate the poles?
3. (Original post by Stonebridge)
Generally the field between two poles isn't uniform. If the field is strong and the poles are close together you get a pretty reasonable uniform field. That shows up as straight lines of flux.
But the lines of flux coming out of magnetic poles are not straight, and as you move the poles further apart, more of the lines go off to the side and fewer directly between the poles.

Common sense should tell you that as the poles move further away, the field gets weaker. If they are moved to infinity the field is zero. The flux density is a measure of how strong the field is. So how can this remain constant as you separate the poles?
Oh yeah, field lines try to spread out as much as they can and when moving the poles further apart they are allowed to do so and will.

Thank you very much for helping

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Updated: November 15, 2013
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