What is SI unit?
SI unit is an abbreviation of International System of Units which is widely used as a measurement system. The reason why SI units were derived is to make it easier to calculate worldwide. Other reasons why SI units were developed are because of CGS (centimetre-gram-second) and MKS (metre-kilogram-second) systems were insufficient to provide measurements for electrostatic and electromagnetic units. But there are countries which do not follow SI unit system and they are Myanmar, United States and Liberia. SI units are set of base units, derived units and prefixes that are used in Physics.
SI base units:
These are units which are used in science and technology for dimensional analysis which are independent of dimensions.
There are total seven base units and they are:
|Mole||mol||Amount of substance||N|
SI derived units:
These are units derived from seven base SI units that are either product of one or more base SI units or dimensionless.
There are a total of twenty-two derived SI units and few of them are given below:
|Name||Symbol||Unit used for|
|Hertz||Hz||Unit of vibration|
|Ohm||Ω||Unit of electrical resistance|
|Newton||N||Unit of force|
|Joule||J||Unit of work|
|Weber||Wb||Unit of magnetic flux|
In order to produce multiples and submultiples of the original unit, prefixes are used in unit names. All these prefixes are integers of powers ten and above hundred or below hundredth are having powre of thousand.
Following is the table with few prefixes that are used in International System of Units:
|Prefix||Symbol||Base 1000||Base 10||
|Short scale||Long scale|
Non-SI units accepted for use with SI
There are many non-SI units that are used in commercial, scientific and technical literature. Following is the group of non-SI units:
- Non-SI units accepted for use with the SI: There are units of time and angle like radian which are used in mathematics, but these are difficult to navigate.
- Non-SI units obtained by experiments: Units like dalton or atomic mass unit are the units that are used on the basis of natural phenomenon that equivalent to SI unit.
- Non-SI units associated with CGS and CGS-Gaussian system of units: Units like gauss, gal, stokes are the units used in classical and relativistic electrodynamics.
International System of quantities
International System of quantities (ISQ) are the equations and quantities that provide the context of SI units. In 2009, ISQ was defined in international standard ISO 80000-1. The basic seven base units are used to underlay the quantities of ISQ and quantities like area, electric resistance and pressure are derived from non-contradictory equations.
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