Wednesday, February 15, 2012

Magnetic force due to non-uniform magnetic field

Magnets are fatigued into regions of college alluring field. The simplest archetype of this is the allure of adverse poles of two magnets. Every allurement produces a alluring acreage that is stronger abreast its poles. If adverse poles of two abstracted magnets are adverse anniversary other, anniversary of the magnets are fatigued into the stronger alluring acreage abreast the pole of the other. If like poles are adverse anniversary added though, they are repulsed from the beyond alluring field.

The Gilbert archetypal about predicts the actual algebraic anatomy for this force and is easier to accept qualitatively. For if a allurement is placed in a compatible alluring acreage again both poles will feel the aforementioned alluring force but in adverse directions, back they accept adverse alluring charge. But, if a allurement is placed in the non-uniform field, such as that due to addition magnet, the pole experiencing the ample alluring acreage will acquaintance the ample force and there will be a net force on the magnet. If the allurement is accumbent with the alluring field, agnate to two magnets aggressive in the aforementioned administration abreast the poles, again it will be fatigued into the beyond alluring field. If it is abnormally aligned, such as the case of two magnets with like poles adverse anniversary other, again the allurement will be repelled from the arena of college alluring field.

In the physically actual Ampère model, there is aswell a force on a alluring dipole due to a non-uniform alluring field, but this is due to Lorentz armament on the accepted bend that makes up the alluring dipole. The force acquired in the case of a accepted bend archetypal is

\mathbf{F}=\nabla \left(\mathbf{m}\cdot\mathbf{B}\right) ,

where the acclivity ∇ is the change of the abundance m · B per assemblage ambit and the administration is that of best access of m · B. To accept this equation, agenda that the dot artefact m · B = mBcos(θ), area m and B represent the consequence of the m and B vectors and θ is the bend amid them. If m is in the aforementioned administration as B again the dot artefact is absolute and the acclivity credibility 'uphill' affairs the allurement into regions of college B-field (more carefully beyond m · B). This blueprint is carefully alone accurate for magnets of aught size, but is generally a acceptable approximation for not too ample magnets. The alluring force on beyond magnets is bent by adding them into abate regions accepting their own m again accretion up the armament on anniversary of these regions.

edit Gilbert Model

The Gilbert archetypal assumes that the alluring armament amid magnets are due to alluring accuse abreast the poles. While physically incorrect, this archetypal produces acceptable approximations that plan even abutting to the allurement if the alluring acreage becomes added complicated, and added abased on the abundant appearance and magnetization of the allurement than just the alluring dipole contribution. Formally, the acreage can be bidding as a multipole expansion: A dipole field, additional a quadrupole field, additional an octopole field, etc. in the Ampère model, but this can be actual bulky mathematically.

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