Physics 1st Chapter -World standard of Measurement :--

 World standard of Measurement :--

Standard of Length:----

(I)Earth Size as Standard of Length:-
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Paris academy of science in the year 1791 suggested a length standard called ''metre''.
# it is defined by paris academy of science 1 meter is One-ten millionth of the distance from the equator to North pole along the median line through Paris.
(II) Metre Bar as Standard of Length :--
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The international committee on weights and measures  adopted a  chemically stable metre bar of  platinum (90%) iridium(10% )alloys as standard of length.

#The distance between two lines engraved on gold plugs near the two ends of the platinum- iridium bar maintened at 0'C is considered to be one metre.
#This primary standard bar is preserved at the international Bureau of weights and measures at servers near Paris.

(III) Atomic standard of length :-
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In October 14, 1960 , the international scientific community agree to accept an atomic constant, namely wavelength of orange red light emitted by  Krypton-86 as a standard of length.

# 1 meter is 1,650,763.73 times the wavelength of orange red light of krypton-86.

(IV) Speed of light as Standard of length:-
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This is based on the distance travelled by light in vacuum.
A metre is the distance travelled by light in vacuum in    1/2,99 ,792,458          Second.

Standard of Mass :-
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(I) A Cylinder of a platinum Indium alloy, preserved at International Bureau of weights and measures at Severes near Paris,is designated as One Kilogram.

Standard of Time:-
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(I)Mean solar day As standard of Time:-
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1 second is defined as 1/86,400 of a mean solar day. The mean solar day is the average of  the time taken for one complete notation of earth around its own axis. This time is called  'Sideral time'.
(II) Tropical Year as Standard of Time :-
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In this case 1 second is defined as
1/31,556,925.9747 part of the Tropical year 1900 This time is called as 'Ephemeris time'.

(III) Atomic standard of Time:-
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In 1967, an atomic standard was adopted basing on a define periodic vibration of Cs-133 atom.
#One second is defined as the time required for 9192 631 770 cycles of the radiation corresponding to transition between the two hyperfine levels of the ground state of Cs-133 atom.

Standard of Current:-
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It is based on the force between two long parallel wires carrying same current.One UN ampere is that current which on flowing through two parallel conductors of infinite length and negligible processor and a place to 1 m apart in vacuum produces a mutual force of 2X10-7 Newton per Metre of each wire.
Standard of Temperature:-
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The Standard is defined on the basis of a thermodynamical scale of temperature in which zero point is at  absolute zero and reference point is the triple point of water.
Kellvin is the fraction 1/27316 of the triple point of water.

Standard of intensity of light :-
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One Candela is defenders the luminous intensity in the derection normal to the surface of 1/6,00,000 metre square of a black body the temperature of Solidification of a platinum at normal atmospheric pressure.

Standard of Amount of Substance:-
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One Mole is the amount of substance having ........