Magnetic Force Inverse Cubed Law?

In summary: Think,A "monopole" field goes like 1/r2. Magnetic monopoles don't actually exist as far as we know to date, but some situations can produce a field which is approximately a monopole field over a limited region. For example, if you have a long bar magnet and you stay close to one pole.A "dipole" field goes like 1/r3. This is what you get from a current loop or a bar magnet, when you get far enough away that it appears "small."Actually Dazza95 is more correct.The inverse square law applies even in real world applications where the magnet is sufficiently asymmetrical to represent a "virtual" monopole.Here
  • #1
Da Apprentice
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I was reading <crackpot link removed> and was wondering if the inverse cube law for magnetic force still applied for situations where the object being attracted isn't another magnet itself? E.g. if there is an electromagnet attracting an iron nut is the rule still inverse cube and not inverse square?

Thanks,
Z.C
 
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  • #4
Think,
A "monopole" field goes like 1/r2. Magnetic monopoles don't actually exist as far as we know to date, but some situations can produce a field which is approximately a monopole field over a limited region. For example, if you have a long bar magnet and you stay close to one pole.
A "dipole" field goes like 1/r3. This is what you get from a current loop or a bar magnet, when you get far enough away that it appears "small."
 
  • #5
Actually Dazza95 is more correct.

The inverse square law applies even in real world applications where the magnet is sufficiently asymmetrical to represent a "virtual" monopole.

Here is a link to an experiment which proves this assertion. The "bar magnet" in this experiment had an aspect ratio of over 100:1

http://www.u-picardie.fr/~dellis/Documents/PhysicsEducation/general%20rule%20for%20the%20variation%20of.pdf

I would surmise that in dipole magnets that are more symmetrical, the opposite pole is close enough to have a substantial influence on the overall net readings such as to reduce the field strength much more radically as the distance increases than with longer more asymmetric magnets where the opposite pole is at rather great distance . . .

Unfortunately most physics sources (wrongly) simply throw out the dogma that magnetic field with increasing distance is the inverse cube - - when it is not when extreme aspect ratios are encountered.

This is an important distinction.



willem2 said:
There would be an inverse square law for magnetic monopoles, but these don't exist as far as we know. A magnetic dipole produces a field that follows an inverse cube law.

see:

http://en.wikipedia.org/wiki/Force_between_magnets
 
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Related to Magnetic Force Inverse Cubed Law?

1. What is the magnetic force inverse cubed law?

The magnetic force inverse cubed law states that the force between two magnetic poles is inversely proportional to the cube of the distance between them. This means that as the distance between the two poles increases, the force between them decreases significantly.

2. How does the magnetic force inverse cubed law differ from the inverse square law?

The inverse square law states that the force between two objects is inversely proportional to the square of the distance between them. In contrast, the magnetic force inverse cubed law is specific to the force between two magnetic poles and involves the cube of the distance instead of the square.

3. What factors affect the strength of the magnetic force according to the inverse cubed law?

The strength of the magnetic force between two poles is affected by the strength of the poles themselves and the distance between them. The closer the poles are, the stronger the force will be. The strength of the poles can also be increased by using stronger magnetic materials.

4. How is the magnetic force inverse cubed law used in everyday life?

The magnetic force inverse cubed law is used in various technologies, such as speakers, motors, and generators. It is also used in medical imaging techniques, such as MRI machines, which use strong magnetic fields to produce images of the inside of the body.

5. Can the magnetic force inverse cubed law be applied to non-magnetic materials?

No, the magnetic force inverse cubed law only applies to magnetic materials and the force between two magnetic poles. It does not apply to non-magnetic materials or forces between non-magnetic objects.

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