100Gauss's laws

Gauss's law

In physics, Gauss's law, also known as Gauss's flux theorem, is a law relating the distribution of electric charge to the resulting electric field. Gauss's law states that:

The electric flux through any closed surface is proportional to the enclosed electric charge.

It is one of the four Maxwell's equations, which form the basis of classical electrodynamics, and is also closely related to Coulomb's law. The law was formulated by Carl Friedrich Gauss in 1835, but was not published until 1867.

Gauss's law has two forms, an integral form and a differential form. They are related by the divergence theorem, also called "Gauss's theorem". Each of these forms can also be expressed two ways: In terms of a relation between the electric field E and the total electric charge, or in terms of the electric displacement field D and the free electric charge. (The former is given in sections 1 and 2, the latter in Section 3.)

Gauss's law has a close mathematical similarity with a number of laws in other areas of physics. See, for example, Gauss's law for magnetism and Gauss's law for gravity. In fact, any "inverse-square law" can be formulated in a way similar to Gauss's law: For example, Gauss's law itself is essentially equivalent to the inverse-square Coulomb's law, and Gauss's law for gravity is essentially equivalent to the inverse-square Newton's law of gravity. See the article Divergence theorem for more detail.

Gauss's law can be used to demonstrate that there is no electric field inside a Faraday cage with no electric charges. Gauss's law is something of an electrical analogue of Ampère's law, which deals with magnetism. Both equations were later incorporated into Maxwell's equations.

Gauss line[]

5-gauss line

5-gauss line with 1.5T magnet

This line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than five gauss. Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public. Portable devices requiring a separation distance between the device and the MR magnet, should not be considered 'MR Safe', 'MR Compatible', or intended for use in the MR environment. Typically the 5 gauss line is the only location where the static magnetic field strength is specified around a MR scanner. Therefore, labeling specifying a separation distance between the MR magnet and the device to ensure safe or proper operation of the device should be avoided.[1]


  1. MRI Technology Portal. "5-gauss line". acessdate 12/14/2014.