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- Dictionarybase unit
noun
- 1. a fundamental unit that is defined arbitrarily and not by combinations of other units. The base units of the SI system are the metre, kilogram, second, ampere, kelvin, mole, and candela.
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The SI base units, or Systéme International d'unités, consists of the metre, kilogram, second, ampere, kelvin, mole and candela. A unit multiple (or multiple of a unit) is an integer multiple of a given unit; likewise a unit submultiple (or submultiple of a unit) is a submultiple or a unit fraction of a given unit. [1]
Contents. SI base unit. The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all other SI units can be derived. The units and their physical quantities are the ...
- Length: Meter (m) The meter is the metric unit of length. It's defined as the length of the path light travels in a vacuum during 1/299,792,458 of a second.
- Mass: Kilogram (kg) The kilogram is the metric unit of mass. It's the mass of the international prototype of the kilogram: a standard platinum/iridium 1 kg mass housed near Paris at the International Bureau of Weights and Measures (BIPM).
- Time: Second (s) The basic unit of time is the second. The second is defined as the duration of 9,192,631,770 oscillations of radiation corresponding to the transition between the two hyperfine levels of cesium-133.
- Electric current: Ampere (A) The basic unit of electric current is the ampere. The ampere is defined as the constant current that, if maintained in two infinitely long straight parallel conductors with a negligible circular cross-section and placed 1 m apart in a vacuum, would produce a force between the conductors equal to 2 x 10-7 newtons per meter of length.
m. Length or distance. The metre is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m s−1, where the second is defined in terms of the caesium frequency ΔνCs. The metre is a unit of distance and is the basis for measuring length, area and volume.
- Second – Unit of Time. Symbol: s. The second is defined by taking the fixed numerical value of the cesium frequency ∆ν, the unperturbed ground-state hyperfine transition frequency of the cesium-133 atom, to be 9,192,631,770 when expressed in the unit Hz, which is equal to s.
- Meter – Unit of Length. Symbol: m. The meter is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299,792,458 when expressed in the unit m s, where the second is defined in terms of ∆ν.
- Kilogram – Unit of Mass. Symbol: kg. The kilogram is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015 ×10 when expressed in the unit J s, which is equal to kg m2 s, where the meter and the second are defined in terms of c and ∆ν.
- Ampere – Unit of Electric Current. Symbol: A. The ampere is defined by taking the fixed numerical value of the elementary charge e to be 1.602176634 × 10 when expressed in the unit C, which is equal to A s, where the second is defined in terms of ∆ν.
Jun 2, 2021 · The SI base units are standard units of measurement in the International System of Units (SI) for seven base quantities. All other SI units are derived from this simple set of seven units. Here is a list of the SI base units, their abbreviations, and a look at their current and past definition. The Seven SI Base Units
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The base units and the derived units formed as the product of powers of the base units with a numerical factor of one form a coherent system of units. Every physical quantity has exactly one coherent SI unit. For example, 1 m/s = 1 m / (1 s) is the coherent derived unit for velocity.
