Which one is correct for S.I. units?
options:-
a)They do not change with place or time
b)Different countries follow different S.I. units.
c)They are adopted from F.P.S system
Answers
Answer:
The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second (the unit of time with the symbol s), metre (length, m), kilogram (mass, kg), ampere (electric current, A), kelvin (thermodynamic temperature, K), mole (amount of substance, mol), and candela (luminous intensity, cd). The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units.[a] Twenty-two derived units have been provided with special names and symbols.[b] The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units,[c] which are adopted to facilitate measurement of diverse quantities. The SI also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten (i.e. decimal) multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.
The SI logo, produced by the BIPM, showing the seven SI base units and the seven defining constants[1]
SI base units
Symbol
Name
Quantity
s
second
time
m
metre
length
kg
kilogram
mass
A
ampere
electric current
K
kelvin
thermodynamic temperature
mol
mole
amount of substance
cd
candela
luminous intensity
SI defining constants
Symbol
Name
Exact value
ΔνCs
hyperfine transition frequency of Cs
9192631770 Hz
c
speed of light
299792458 m/s
h
Planck constant
6.62607015×10−34 J⋅s
e
elementary charge
1.602176634×10−19 C
k
Boltzmann constant
1.380649×10−23 J/K
NA
Avogadro constant
6.02214076×1023 mol−1
Kcd
luminous efficacy of 540 THz radiation
683 lm/W
Since 2019, the magnitudes of all SI units have been defined by declaring exact numerical values for seven defining constants when expressed in terms of their SI units. These defining constants are the speed of light in vacuum, c, the hyperfine transition frequency of caesium ΔνCs, the Planck constant h, the elementary charge e, the Boltzmann constant k, the Avogadro constant NA, and the luminous efficacy Kcd. The nature of the defining constants ranges from fundamental constants of nature such as c to the purely technical constant Kcd. Prior to 2019, h, e, k, and NA were not defined a priori but were rather very precisely measured quantities. In 2019, their values were fixed by definition to their best estimates at the time, ensuring continuity with previous definitions of the base units. One consequence of the redefinition of the SI is that the distinction between the base units and derived units is in principle not needed, since any unit can be constructed directly from the seven defining constants.[2]:129
The current way of defining the SI is a result of a decades-long move towards increasingly abstract and idealised formulation in which the realisations of the units are separated conceptually from the definitions. A consequence is that as science and technologies develop, new and superior realisations may be introduced without the need to redefine the unit. One problem with artefacts is that they can be lost, damaged, or changed; another is that they introduce uncertainties that cannot be reduced by advancements in science and technology. The last artefact used by the SI was the International Prototype of the Kilogram, a cylinder of platinum-iridium.
The original motivation for the development of the SI was the diversity of units that had sprung up within the centimetre–gram–second (CGS) systems (specifically the inconsistency between the systems of electrostatic units and electromagnetic units) and the lack of coordination between the various disciplines that used them. The General Conference on Weights and Measures (French: Conférence générale des poids et mesures – CGPM), which was established by the Metre Convention of 1875, brought together many international organisations to establish the definitions and standards of a new system and to standardise the rules for writing and presenting measurements. The system was published in 1960 as a result of an initiative that began in 1948, so it is based on the metre–kilogram–second system of units (MKS) rather than any variant of the CGS.
Introduction
Answer:
a) A unit is said to be a standard if it does not change with respect to space and time.
For example, the time has a standard unit 'second
b) Only three countries – the U.S., Liberia and Myanmar
all over world follow this country S.I unit only
c)The foot pound second system or (FPS )system is a system of units built on the three fundamental units foot for length, pound for either mass and second for time
Mark me brainiest pls