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S.I. base units and derived units
S.I. base units and derived units
Published: 2015/09/16
Channel: Cowen Physics
Scientific Units the SI System and Metric Units - Chemistry
Scientific Units the SI System and Metric Units - Chemistry
Published: 2011/10/10
Channel: Mr. Causey
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SI Base Units
Published: 2010/10/07
Channel: National Physical Laboratory
A Level Physics - Base Units
A Level Physics - Base Units
Published: 2015/01/19
Channel: A Level Physics Online
Prefixes used with the base units
Prefixes used with the base units
Published: 2011/09/08
Channel: Alom Shaha
Units of Measure: Scientific Measurements & SI System
Units of Measure: Scientific Measurements & SI System
Published: 2016/03/05
Channel: ProEdify
SI base unit
SI base unit
Published: 2014/10/16
Channel: Audiopedia
SI Units Part One: The Second
SI Units Part One: The Second
Published: 2013/02/12
Channel: Because We Can- The Channel
SI Units and Metric Conversions
SI Units and Metric Conversions
Published: 2014/09/07
Channel: Nicole Stratton
Derived Units of SI Base Units
Derived Units of SI Base Units
Published: 2016/01/28
Channel: lscphysics
The metre
The metre
Published: 2010/10/06
Channel: National Physical Laboratory
SI Base units (IN URDU / HINDI)
SI Base units (IN URDU / HINDI)
Published: 2015/12/20
Channel: Pharero Academy
SI base units (IN URDU / HINDI)
SI base units (IN URDU / HINDI)
Published: 2015/12/23
Channel: Pharero Academy
A Brief discussion of SI Base Units
A Brief discussion of SI Base Units
Published: 2013/06/11
Channel: James Roaden
S I  base units and derived units
S I base units and derived units
Published: 2017/06/12
Channel: Love Basheer
What are SI units ?
What are SI units ?
Published: 2016/07/31
Channel: winscience
DEFINITIONS OF SI BASE UNITS
DEFINITIONS OF SI BASE UNITS
Published: 2017/02/16
Channel: 7activestudio
SI, Base and Derived Units
SI, Base and Derived Units
Published: 2015/09/23
Channel: Revision
A Level Physics: General Science Skills: SI and Base Units
A Level Physics: General Science Skills: SI and Base Units
Published: 2016/08/31
Channel: Burrows Physics
Unit Conversion & Significant Figures: Crash Course Chemistry #2
Unit Conversion & Significant Figures: Crash Course Chemistry #2
Published: 2013/02/19
Channel: CrashCourse
The second
The second
Published: 2010/10/06
Channel: National Physical Laboratory
S.I. units  #2 - Length, the Metre
S.I. units #2 - Length, the Metre
Published: 2013/09/12
Channel: Lincoln Central
SI base units and other derived units
SI base units and other derived units
Published: 2014/06/21
Channel: Understanding Physics
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Base Units of SI and Scientific Notation
Published: 2012/09/08
Channel: Massimo Bozzi
SI System ( significance and Base units )- By Vineet Khatri
SI System ( significance and Base units )- By Vineet Khatri
Published: 2016/09/15
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SI Base Units - A Level Physics Exam Practice Question - Multiple Choice
SI Base Units - A Level Physics Exam Practice Question - Multiple Choice
Published: 2017/01/18
Channel: GorillaPhysics
Express the Voltage in terms of the  relevant SI fundamental units.
Express the Voltage in terms of the relevant SI fundamental units.
Published: 2016/12/07
Channel: Andrew Jones
Basics of Chemistry: Units of measurement in chemistry
Basics of Chemistry: Units of measurement in chemistry
Published: 2015/08/31
Channel: Dr. B's Chemistry
SI Base Units Explained - Part 1
SI Base Units Explained - Part 1
Published: 2010/08/23
Channel: owigger
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Derive SI Base Units for Special Units
Published: 2016/01/15
Channel: lscphysics
SI Units and Density
SI Units and Density
Published: 2014/11/05
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converting to base units
converting to base units
Published: 2014/09/29
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Physics of Life / SI Units
Published: 2009/11/18
Channel: ESFTV
SI Base Units
SI Base Units
Published: 2016/11/19
Channel: Erudite Esotericist
FUNDAMENTAL UNITS
FUNDAMENTAL UNITS
Published: 2016/02/09
Channel: 7activestudio
XI_6.Fundamental Units definitions.mp4
XI_6.Fundamental Units definitions.mp4
Published: 2012/04/26
Channel: Pradeep Kshetrapal
What Is The Unit Of Time?
What Is The Unit Of Time?
Published: 2017/07/14
Channel: sparky SPARKS
The kelvin
The kelvin
Published: 2010/10/06
Channel: National Physical Laboratory
Conversion of SI Unit to Its Base Unit | Introduction to Physics
Conversion of SI Unit to Its Base Unit | Introduction to Physics
Published: 2014/07/14
Channel: myhometuition
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The kilogram
Published: 2010/10/06
Channel: National Physical Laboratory
deriving equation by using base SI units
deriving equation by using base SI units
Published: 2015/12/24
Channel: Pharero Academy
Units and measurements part 1 : Base units, derived units and the SI system
Units and measurements part 1 : Base units, derived units and the SI system
Published: 2016/08/12
Channel: Physics ab initio
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Published: 2014/11/05
Channel: OCHS Physics
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Published: 2015/01/12
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Published: 2012/02/13
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Published: 2013/08/22
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Ch 7. Fundamental Dimensions and Base Units
Published: 2017/02/23
Channel: Jangwoon Park
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What Is The Unit Of Acceleration In The SI System?
Published: 2017/07/22
Channel: tell sparky
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Derived Quantities - Studi Physics
Published: 2014/06/17
Channel: Binogi
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What Is The SI Unit Of Mass?
Published: 2017/07/14
Channel: sparky SPARKS
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WIKIPEDIA ARTICLE

From Wikipedia, the free encyclopedia
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The seven SI base units and the interdependency of their definitions: for example, to extract the definition of the metre from the speed of light, the definition of the second must be known while the ampere and candela are both dependent on the definition of energy which in turn is defined in terms of length, mass and time.

The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units and their physical quantities are the metre for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the candela for luminous intensity, and the mole for amount of substance.

The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology.

The names and symbols of SI base units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter. For example, the metre (US English: meter) has the symbol m, but the kelvin has symbol K, because it is named after Lord Kelvin and the ampere with symbol A is named after André-Marie Ampère.

Several other units, such as the litre (US English: liter), are formally not part of the SI, but are accepted for use with SI.

Seven SI base units[edit]

SI base units
Name Symbol Measure Current (2005) formal definition[1] Historical origin / justification Dimension
symbol
metre m length "The metre is the length of the path travelled by light in vacuum during a time interval of 1  299792458 of a second."
17th CGPM (1983, Resolution 1, CR, 97)
 10,000,000 of the distance from the Earth's equator to the North Pole measured on the circumference through Paris. L
kilogram kg mass "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram."
3rd CGPM (1901, CR, 70)
The mass of one litre of water at the temperature of melting ice. A litre is one thousandth of a cubic metre. M
second s time "The second is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."
13th CGPM (1967/68, Resolution 1; CR, 103)
"This definition refers to a caesium atom at rest at a temperature of 0 K."
(Added by CIPM in 1997)
The day is divided in 24 hours, each hour divided in 60 minutes, each minute divided in 60 seconds.
A second is 1  (24 × 60 × 60) of the day.
T
ampere A electric current "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length."
9th CGPM (1948)
The original "International Ampere" was defined electrochemically as the current required to deposit 1.118 milligrams of silver per second from a solution of silver nitrate. Compared to the SI ampere, the difference is 0.015%. I
kelvin K thermodynamic temperature "The kelvin, unit of thermodynamic temperature, is the fraction 1  273.16 of the thermodynamic temperature of the triple point of water."
13th CGPM (1967/68, Resolution 4; CR, 104)
"This definition refers to water having the isotopic composition defined exactly by the following amount of substance ratios: 0.000 155 76 mole of 2H per mole of 1H, 0.000 379 9 mole of 17O per mole of 16O, and 0.002 005 2 mole of 18O per mole of 16O."
(Added by CIPM in 2005)
The Celsius scale: the Kelvin scale uses the degree Celsius for its unit increment, but is a thermodynamic scale (0 K is absolute zero). Θ
mole mol amount of substance "1. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is 'mol'.

2. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles."
14th CGPM (1971, Resolution 3; CR, 78)
"In this definition, it is understood that unbound atoms of carbon 12, at rest and in their ground state, are referred to."
(Added by CIPM in 1980)

Atomic weight or molecular weight divided by the molar mass constant, 1 g/mol. N
candela cd luminous intensity "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian."
16th CGPM (1979, Resolution 3; CR, 100)
The candlepower, which is based on the light emitted from a burning candle of standard properties. J
Name Symbol Measure Current (2005) formal definition[1] Historical origin / justification Dimension
symbol

Proposed redefinitions[edit]

Proposed SI System: Dependence of base unit definitions on physical constants with fixed numerical values and on other base units that are derived from the same set of constants.

The definitions of the base units have been modified several times since the Metre Convention in 1875, and new additions of base units have occurred. Since the redefinition of the metre in 1960, the kilogram is the only unit that is directly defined in terms of a physical artifact, rather than a property of nature. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinumiridium cylinder stored in a vault near Paris.

It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, in the same way that the metre is now defined in terms of the speed of light. The 21st General Conference on Weights and Measures (CGPM, 1999) placed these efforts on an official footing, and recommended "that national laboratories continue their efforts to refine experiments that link the unit of mass to fundamental or atomic constants with a view to a future redefinition of the kilogram." Two possibilities have attracted particular attention: the Planck constant and the Avogadro constant.

In 2005, the International Committee for Weights and Measures (CIPM) approved preparation of new definitions for the kilogram, the ampere, and the kelvin and it noted the possibility of a new definition of the mole based on the Avogadro constant.[2] The 23rd CGPM (2007) decided to postpone any formal change until the next General Conference in 2011.[3][needs update]

In a note to the CIPM in October 2009,[4] Ian Mills, the President of the CIPM Consultative Committee - Units (CCU) catalogued the uncertainties of the fundamental constants of physics according to the current definitions and their values under the proposed new definition. He urged the CIPM to accept the proposed changes in the definition of the kilogram, ampere, kelvin, and mole so that they are referenced to the values of the fundamental constants, namely the Planck constant (h), the electron charge (e), the Boltzmann constant (k), and the Avogadro constant (NA).[5]

See also[edit]

References[edit]

External links[edit]

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