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In physics (specifically electromagnetism), Gauss's law, also known as Gauss's flux theorem (or sometimes Gauss's theorem), is one of Maxwell's equations. It is an application of the divergence theorem , and it relates the distribution of electric charge to the resulting electric field .
If magnetic monopoles were to be discovered, then Gauss's law for magnetism would state the divergence of B would be proportional to the magnetic charge density ρ m, analogous to Gauss's law for electric field. For zero net magnetic charge density (ρ m = 0), the original form of Gauss's magnetism law is the result.
Gauss's law for magnetism: magnetic field lines never begin nor end but form loops or extend to infinity as shown here with the magnetic field due to a ring of current. Gauss's law for magnetism states that electric charges have no magnetic analogues, called magnetic monopoles; no north or south magnetic poles exist in isolation. [3]
Any inverse-square law can instead be written in a Gauss's law-type form (with a differential and integral form, as described above). Two examples are Gauss's law (in electrostatics), which follows from the inverse-square Coulomb's law, and Gauss's law for gravity, which follows from the inverse-square Newton's law of universal gravitation. The ...
A true magnetic monopole would be a new elementary particle, and would violate Gauss's law for magnetism ∇⋅B = 0. A monopole of this kind, which would help to explain the law of charge quantization as formulated by Paul Dirac in 1931, [40] has never been observed in experiments. [41] [42]
[3]: 192 Substituting this in Gauss's law gives =. Thus, the divergence of the magnetization, ∇ ⋅ M , {\displaystyle \nabla \cdot \mathbf {M} ,} has a role analogous to the electric charge in electrostatics [ 4 ] and is often referred to as an effective charge density ρ M {\displaystyle \rho _{M}} .
While Gauss's law holds for all situations, it is most useful for "by hand" calculations when high degrees of symmetry exist in the electric field. Examples include spherical and cylindrical symmetry. The SI unit of electric flux is the volt-meter (V·m), or, equivalently, newton-meter squared per coulomb (N·m 2 ·C −1).
In particular, it represents lines of inverse-square law force. The extension of the above considerations confirms that where B is to H, and where J is to ρ, then it necessarily follows from Gauss's law and from the equation of continuity of charge that E is to D i.e. B parallels with E, whereas H parallels with D.