In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather...
76 KB (9,061 words) - 16:56, 10 June 2025
Dalton (unit) (category Units of chemical measurement)
units of mass. The 2019 revision of the SI redefined the kilogram by fixing the value of the Planck constant (h), improving the precision of the atomic...
39 KB (4,159 words) - 04:06, 6 July 2025
Avogadro constant (category Amount of substance)
determination of the number of atoms in 12 grams of carbon-12 (12C) before the 2019 revision of the SI, i.e. the gram-to-dalton mass-unit ratio, g/Da. Both the constant...
23 KB (2,738 words) - 23:25, 14 July 2025
Mole (unit) (redirect from The Mol)
With the 2019 revision of the SI, the numerical equivalence is now only approximate, but may still be assumed with high accuracy. Conceptually, the mole...
29 KB (3,714 words) - 16:30, 13 June 2025
On 20 May 2019, as the final act of the 2019 revision of the SI, the BIPM officially introduced the following new definitions, replacing the preceding...
13 KB (803 words) - 17:25, 16 September 2024
Austrian scientist Ludwig Boltzmann. As part of the 2019 revision of the SI, the Boltzmann constant is one of the seven "defining constants" that have been...
26 KB (2,946 words) - 19:42, 11 July 2025
Gas constant (category Amount of substance)
the 2019 revision of the SI, both NA and k are defined with exact numerical values when expressed in SI units. As a consequence, the SI value of the molar...
17 KB (1,839 words) - 08:41, 31 May 2025
Triple point (section Triple point of water)
the 2019 revision of the SI, where the kelvin was redefined so that the Boltzmann constant is exactly 1.380649×10−23 J⋅K−1, and the triple point of water...
18 KB (1,349 words) - 08:05, 15 July 2025
Faraday constant (category Units of electrical charge)
Since the 2019 revision of the SI, the Faraday constant has an exactly defined value, the product of the elementary charge (e, in coulombs) and the Avogadro...
5 KB (487 words) - 14:12, 4 June 2025
Elementary charge (redirect from Charge of the electron)
value of the elementary charge is exactly e = 1.602176634×10−19 C or 160.2176634 zeptocoulombs (zC). Since the 2019 revision of the SI, the seven SI base...
22 KB (2,582 words) - 13:26, 3 June 2025
Ampere (category SI base units)
(1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted. As of the 2019 revision of the SI, the ampere is defined...
16 KB (1,723 words) - 06:41, 25 July 2025
Electronvolt (category Units of chemical measurement)
coulombs (symbol C). Under the 2019 revision of the SI, this sets 1 eV equal to the exact value 1.602176634×10−19 J. Historically, the electronvolt was devised...
17 KB (1,967 words) - 08:01, 21 July 2025
Ohm (category SI derived units)
1861. Following the 2019 revision of the SI, in which the ampere and the kilogram were redefined in terms of fundamental constants, the ohm is now also...
27 KB (2,880 words) - 22:52, 6 July 2025
the 2019 revision of the SI, the Josephson constant has an exact value of KJ = 483597.84841698... GHz⋅V−1. The following physical equations use SI units...
15 KB (1,811 words) - 06:19, 27 June 2025
kelvin in terms of invariant constants of physics, ultimately resulting in the 2019 revision of the SI, which finally eliminated the need for any physical...
105 KB (12,426 words) - 17:44, 26 June 2025
Ideal gas (section Types of ideal gas)
compared to the empty space between them. One mole of an ideal gas has a volume of 22.71095464... L (exact value based on 2019 revision of the SI) at standard...
24 KB (3,821 words) - 02:41, 29 April 2025
Relative atomic mass (category Amount of substance)
quantities in the ratio are masses, the resulting value is dimensionless. These definitions remain valid: 134 even after the 2019 revision of the SI. For a...
18 KB (2,332 words) - 05:42, 15 June 2025
Metre (redirect from SI unit of length)
1/299792458 of a second. After the 2019 revision of the SI, this definition was rephrased to include the definition of a second in terms of the caesium frequency...
21 KB (2,768 words) - 22:35, 8 July 2025
metrology, as well as the International System of Units (SI) and Coordinated Universal Time (UTC). It is headquartered in the Pavillon de Breteuil in...
58 KB (6,010 words) - 15:16, 19 July 2025
molecular weight when referring to a weighted average of a sample. Prior to the 2019 revision of the SI, quantities expressed in daltons (Da) were by definition...
12 KB (1,495 words) - 11:48, 5 June 2025
Kelvin (redirect from Kelvin scale of temperature)
definition. The 2019 revision of the SI now defines the kelvin in terms of energy by setting the Boltzmann constant; every 1 K change of thermodynamic temperature...
46 KB (4,930 words) - 19:13, 25 July 2025
Einstein (unit) (category Units of amount of substance)
joule. If it were still in use, as of the 2019 revision of the SI, its value would be related to the frequency of the electromagnetic radiation by 1 einstein...
3 KB (400 words) - 21:46, 4 January 2025
Vacuum permittivity (redirect from Permittivity of free space)
the new quantity q by: q s = q 4 π ε 0 . {\displaystyle \ q_{\text{s}}={\frac {q}{\sqrt {4\pi \varepsilon _{0}}}}.} In the 2019 revision of the SI,...
17 KB (2,262 words) - 19:43, 20 July 2025
Caesium standard (category Wikipedia articles incorporating text from the Federal Standard 1037C)
that of the kilogram. From 1954 to 2019, the SI temperature scales were defined using the triple point of water and absolute zero. The 2019 revision replaced...
21 KB (2,492 words) - 19:17, 17 April 2025
World Metrology Day (category Use dmy dates from July 2019)
as one of UNESCO international days. 2019 revision of the SI "Australia's measurement system". 20 May 2019. Grant, Andrew (2018). "Revamped SI measurement...
2 KB (154 words) - 20:24, 20 May 2025
the International Prototype of the Kilogram and the International Prototype Metre, although both have been superseded during the 2019 revision of the...
5 KB (489 words) - 00:32, 21 October 2024
Rydberg constant (redirect from Rydberg unit of energy)
according to his model of the atom. Before the 2019 revision of the SI, R ∞ {\displaystyle R_{\infty }} and the electron spin g-factor were the most accurately...
12 KB (2,087 words) - 15:24, 11 September 2024
Realisation (metrology) (category Systems of units)
artefacts such as the standard kilogram. Following the 2019 revision of the SI all fundamental units of metrology are now defined in terms of natural physical...
8 KB (808 words) - 15:40, 7 June 2025
historical and practical reasons. See 2019 revision of the SI. A set of base dimensions of quantity is a minimal set of units such that every physical quantity...
10 KB (1,208 words) - 20:27, 9 March 2025
Tesla (unit) (redirect from Tesla (unit of measure))
The tesla (symbol: T) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla...
13 KB (1,364 words) - 11:20, 24 July 2025