How are magnetic fields measured?
The strength of a magnetic field is measured in units of Gauss (G), or alternatively, in Tesla (T). In the MKS (metric) system of units, 1 T = 1 kilogram*ampere/second^2 = 10^4 G. For comparison, the magnetic field of the earth at the surface is on the order of 1 Gauss, where that of a Neodymium magnet is on the order of 10^4 Gauss. This means that Neodymium magnets produce magnetic fields tens of thousands of times stronger than those of the earth! Technically, Gauss and Tesla are units of magnetic induction, also known as magnetic flux density. (This term is described in an earlier question.) Quantitatively, the force on a charged particle q moving with velocity v is given by the vector equation F = qv x B, where B is the magnetic induction. Another common quantity of interest is the corecivity or corercive force of a magnet. Also measured in Gauss, the coercivity is the magnetic field required to demagnetize a material. For example, Neodymium magnets typically have a coercivity of a
The traditional CGS units for measuring magnetic fields are Gauss and Oersted. Magnetic flux density is measured in Gauss, while magnetic field intensity is measured in Oersted. The ratio of B, magnetic flux, in Gauss, to H, magnetic field, in Oersted, is defined as permeability, “” (pronounced “mew”). The B/H ratio, or “”, is a measure of the material’s properties. It is high for ferromagnetic materials. In air, however, Gauss and Oersted are identical numerically. The modern S/I or Metric system prefers the Tesla and Ampere-turns/meter units for magnetic flux density and magnetic field intensity, respectively. Conversions are shown in the table below.
