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Measure for how the magnetization of material is affected by the application of an external magnetic field H/m L M T −2 I −2: intensive Permittivity: ε s: Measure for how the polarization of a material is affected by the application of an external electric field F/m L −3 M −1 T 4 I 2: intensive Plane angle: θ: Ratio of circular arc ...
For example, the base unit of length is the metre, and distances much longer or much shorter than 1 metre are measured in units that are powers of 10 times a metre. This is unlike older systems of units in which the ratio between the units for longer and shorter distances varied: there are 12 inches in a foot, but the number of 5,280 feet in a ...
Every unit of length has a corresponding unit of area, namely the area of a square with the given side length. Thus areas can be measured in square metres (m 2 ), square centimetres (cm 2 ), square millimetres (mm 2 ), square kilometres (km 2 ), square feet (ft 2 ), square yards (yd 2 ), square miles (mi 2 ), and so forth. [ 13 ]
In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric current) and units of measurement (such as metres and grams) and tracking these dimensions as calculations or comparisons are performed.
As the SI Brochure states, [1]: 140 "this applies not only to technical texts, but also, for example, to measuring instruments (i.e. the instrument read-out needs to indicate both the unit and the quantity measured)". Furthermore, the same coherent SI unit may be a base unit in one context, but a coherent derived unit in another.
Size of a pixel on a 17-inch monitor with a resolution of 1024×768 560 μm Thickness of the central area of a human cornea [26] 750 μm Maximum diameter of Thiomargarita namibiensis, the second largest bacterium ever discovered 10 −3: 1 millimeter ~5 mm Length of an average flea is 1–10 mm (usually <5 mm) [27] 2.54 mm
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.
The SI system after 1983, but before the 2019 revision: Dependence of base unit definitions on other base units (for example, the metre is defined as the distance travelled by light in a specific fraction of a second), with the constants of nature and artefacts used to define them (such as the mass of the IPK for the kilogram).