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Derived quantities can be expressed in terms of the base quantities. Note that neither the names nor the symbols used for the physical quantities are international standards. Some quantities are known as several different names such as the magnetic B-field which is known as the magnetic flux density , the magnetic induction or simply as the ...
Even when two physical quantities have identical dimensions, it may nevertheless be meaningless to compare or add them. For example, although torque and energy share the dimension T −2 L 2 M, they are fundamentally different physical quantities. To compare, add, or subtract quantities with the same dimensions but expressed in different units ...
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 ...
The former Weights and Measures office in Seven Sisters, London Units of measurement, Palazzo della Ragione, Padua. A unit of measurement, or unit of measure, is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. [1]
A systems of quantities relates physical quantities, and due to this dependence, a limited number of quantities can serve as a basis in terms of which the dimensions of all the remaining quantities of the system can be defined. A set of mutually independent quantities may be chosen by convention to act as such a set, and are called base quantities.
The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical ...
The fields D, H, P, and M also have the same dimensions as E and B. For vacuum, any expression involving D can simply be recast as the same expression with E. In SI units, D and P have the same units, as do H and M, but they have different units from each other and from E and B.
Examples of non-physical categories are: currency, quality indicator, and colour intensity. Quantities may be grouped together into categories of quantities which are mutually comparable. Lengths, diameters, distances, heights, wavelengths, and so on would constitute such a category. Mutually comparable quantities have the same dimensionality.