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CGS units have been deprecated in favor of SI units by NIST, [7] as well as organizations such as the American Physical Society [8] and the International Astronomical Union. [9] SI units are predominantly used in engineering applications and physics education, while Gaussian CGS units are still commonly used in theoretical physics, describing ...
One difference between the Gaussian and SI systems is in the factor 4π in various formulas that relate the quantities that they define. With SI electromagnetic units, called rationalized, [3] [4] Maxwell's equations have no explicit factors of 4π in the formulae, whereas the inverse-square force laws – Coulomb's law and the Biot–Savart law – do have a factor of 4π attached to the r 2.
Speed or velocity is defined by the change in distance divided by a change in time. The derived unit m/s uses the base units of the SI system. [1] The derived unit km/h requires numerical factors to relate to the SI base units: 1000 m/km and 3600 s/h. In the cgs system, m/s is not a coherent derived unit.
For example, the coherent derived SI unit of velocity is the metre per second, with the symbol m/s. [1]: 139 The base and coherent derived units of the SI together form a coherent system of units (the set of coherent SI units). A useful property of a coherent system is that when the numerical values of physical quantities are expressed in terms ...
Since the 2019 revision of the SI, the seven SI base units are defined in terms of seven fundamental physical constants, of which the elementary charge is one. In the centimetre–gram–second system of units (CGS), the corresponding quantity is 4.803 2047... × 10 −10 statcoulombs. [b]
In the CGS system, the unit of the H-field is the oersted and the unit of the B-field is the gauss.In the SI system, the unit ampere per meter (A/m), which is equivalent to newton per weber, is used for the H-field and the unit of tesla is used for the B-field.
The gal is a derived unit, defined in terms of the centimeter–gram–second (CGS) base unit of length, the centimeter, and the second, which is the base unit of time in both the CGS and the modern SI system. In SI base units, 1 Gal is equal to 0.01 m/s 2.
The CGS-to-SI correspondence of electromagnetic units as given was exact prior to the 2019 revision of the SI, until which the magnetic constant μ 0 was defined as 4π × 10 −7 N⋅A −2. As from the redefinition, μ 0 has an inexactly known value when expressed in SI units, with the exactness of the electromagnetic unit correspondence ...