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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 ...
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density.
It is not defined for ratios of quantities of other kinds. Within the ISQ, all levels are treated as derived quantities of dimension 1. [citation needed] Several units for levels are defined by the SI and classified as "non-SI units accepted for use with the SI units". [4] An example of level is sound pressure level, with the unit of decibel.
For example, the physical quantity mass, symbol m, can be quantified as m=n kg, where n is the numerical value and kg is the unit symbol (for kilogram). Quantities that are vectors have, besides numerical value and unit, direction or orientation in space.
Derived units apply to some derived quantities, which may by definition be expressed in terms of base quantities, and thus are not independent; for example, electrical conductance is the inverse of electrical resistance, with the consequence that the siemens is the inverse of the ohm, and similarly, the ohm and siemens can be replaced with a ...
Gaussian units have only length, mass, and time as base quantities, with no separate electromagnetic dimension. Other quantities, such as power and speed, are derived from the base quantities: for example, speed is distance per unit time. Historically, a wide range of units was used for the same type of quantity.
Derived units are the units of the quantities which are derived from the base quantities and some of the derived units are the units of speed, work, acceleration, energy, pressure etc. [7] Different systems of units are based on different choices of a set of related units including fundamental and derived units.
Many of these quantities are related to each other by various physical laws, and as a result the units of a quantities can be generally be expressed as a product of powers of other units; for example, momentum is mass multiplied by velocity, while velocity is distance divided by time. These relationships are discussed in dimensional analysis.