# Questions tagged [multipole-expansion]

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### From where does this equation of quadrupole potential of a quadrupole mass filter derive from?

Quoting from thesis "Chip-scale quadrupole mass filters for a Micro-Gas Analyzer" (page 23): As I am solving quadrupole mass filter equation, I am stuck from where quadrupole potential ...
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### The puzzling interaction between an anapole moment and external fields

Consider an electrical current distribution with only an [anapole, or toroidal moment] but no electrical or magnetic multipole moments, like this current on a torus: Its magnetic field is completely ...
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### How can a point source emit spherical EM waves when they are forbidden by Maxwell's equations?

I know that there exist plane wave solutions to the Maxwell equations in free space, and I tried solving them for a spherical wave emanating from a point but could find no solution consistent with the ...
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### Why does a group of charges with spherical symmetry, where each oscillates radially while retaining spherical symmetry, not radiate? [duplicate]

I am thinking about the problem, "Why does a group of charges with spherical symmetry, where each oscillates radially while retaining spherical symmetry, not radiate?" I figured out that ...
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### Can an oscillatory field produced by a time-dependent charge distribution fall off faster than $1/r$?

An electric charge has a field that decays at large distances like $1/r^2$. A charge distribution with total charge zero, but with a nonvanishing dipole moment, has a field that decays at large ...
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### Can a point charge be asymmetric?

The derivation of Coulombs law from Maxwell's first equation for a point charge assumes that the field is symmetric along a sphere. What happens if this assumption is removed? Could there be other ...
1 vote
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### Is quadrupole contribution to gravitational potential the sum of the contribution of all $m$ values?

Many of the sources I find on multipole expansions seem to be about electric potential and involve matrices. However, in my classical mechanics class we have not used matrices for multipole expansions ...
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### Is there a Lorentz invariant electromagnetic quadrupole moment tensor?

I'm familiar with the electric and magnetic quadrupole moment tensors. However, I'm bothered that these objects are tensors only in the sense of spatial rotations. After all, Maxwell's equations and ...
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### EM radiation from monopole v.s. dipole

I'm confused about two conflicting ideas: the first is that monopoles cannot emit EM radiation (see here), and the second is that an accelerating point charge does produce EM radiation (see here). I ...
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