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When magnets attract to each other or repel. Should I use Coulombs law? If not, why not? Some would say that I shouldn't because: "Coulomb's law deals with static charges and force due to them. Whereas magnetism is force due to moving charges!"

What do you all think?

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Possible duplicate: – Qmechanic Mar 7 '13 at 19:34

You can't use the formula in Coulomb's law to compute the force between two magnets

  1. because that would describe magnetic monopoles, which do not exist in nature (one of Maxwell's equations, $\vec{\nabla}\cdot \vec{B}=0$ expresses this fact), and more importantly,
  2. because this formula is incorrect. The force between two magnets should look like the formula I just linked to, which does not scale as $\frac{1}{r^2}$ with distance.
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this link is more pertinent where in some approximation one can use an 1/r pole to pole… – anna v Aug 9 '15 at 5:54

One way for finding the field of a magnet is to model it (as a polarized material inside volume $V$ ) with magnetic dipoles , as lots of dipoles near each other , and then sum the produced fields of all dipoles at the desired point.

To find the field of a dipole, You can model it as two (to date, fictitious) magnetic monopoles and use coulomb force law to find its magnetic field or its interaction with other dipoles. The method gives correct result, But the problem with this , is that the situation does not describe the reality .( magnetic poles have not been observed to date)

To put it another way, theoretically , in classical electrodynamics , Maxwell's equations let (and encourage) you define a magnetic charge density. And then , in the static case ( electro- and magneto- static) the complete solution for magnetic field will be given by coulomb's law for magnetic charge.

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Coulomb's Law for magnets is as follows $$F=\frac{\mu}{4\pi}\frac{q_1q_2}{r^2},$$

where: $F$=Force in newtons

$\frac{\mu}{4\pi}$=the constant of proportionality(in this case 0.0000001)

$q_1q_2$= the charge of the magnet poles in coulombs

$r^2$=the distance between the two poles squared

This will give you the force between two magnet poles. The only problem with this equation is figuring out what the coulomb charge rate is of each pole for $q_1q_2$. You need to know what $q_1$ is and what $q_2$ is in order to plug into the equation and solve for $F$.

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