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James Clerk Maxwell played a major role in developing the concept of a coherent CGS system and in extending the metric system to include electrical units.. A coherent system of units is a system of units of measurement used to express physical quantities that are defined in such a way that the equations relating the numerical values expressed in the units of the system have exactly the same ...
Planck units is system of geometrized units in which the reduced Planck constant is included in the list of defining constants. It is based on only properties of free space rather than of any object or particle. Stoney units is a system of geometrized units in which the Coulomb constant and the elementary charge are included.
The systems formalised the concept of a collection of related units called a coherent system of units. In a coherent system, base units combine to define derived units without extra factors. [4]: 2 For example, using metre per second is coherent in a system that uses metre for length and second for time, but kilometre per hour is not coherent.
This definition results in all SI electromagnetic units being numerically consistent (subject to factors of some integer powers of 10) with those of the CGS-EMU system described in further sections. The ampere is a base unit of the SI system, with the same status as the metre, kilogram, and second.
The International System of Units is the modern metric system. It is based on the metre–kilogram–second–ampere (MKSA) system of units from early in the 20th century. [20] It also includes numerous coherent derived units for common quantities like power (watt) and irradience (lumen).
=, where = (SI units) In this system, the unit for charge is defined by setting the Coulomb force constant to unity and the unit for electric potential was defined to ensure the unit of energy calculated by the relation = is one erg. The electrostatic units of measure were the statampere, statvolt, and so on.
A similar system, termed British Engineering Units by Halliday and Resnick (1974), is a system that uses the slug as the unit of mass, and in which Newton's law retains the form F = ma. [5] Modern British engineering practice has used SI base units since at least the late 1970s.
In physics, natural unit systems are measurement systems for which selected physical constants have been set to 1 through nondimensionalization of physical units.For example, the speed of light c may be set to 1, and it may then be omitted, equating mass and energy directly E = m rather than using c as a conversion factor in the typical mass–energy equivalence equation E = mc 2.