DEFINITIONS OF BASIC and SUPPLEMENTARY UNIT
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITmetre ( SI unit of
Length)1m is defined as length of path travelled by light in vacuum
in 1/299792458 th of a second.(1,650,763.73 wavelengths in vacuum
of radiation corresponding to orange red light of Krypton-86)
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITkilogram ( SI unit of
mass )The mass of a cylinder made of platinum-iridium alloy kept at
International Bureau of Weights and Measures is defined as 1 kg
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITkelvin ( SI unit of
Temperature)1 K is defined as fraction 1/273.16 of the
thermodynamic temperature of triple point of water
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITampere ( SI unit of
Electric current) 1 ampere is a constant current that will produce
an attractive force of 2107newtonper metre of length between two
straight, parallel conductors of infinite length and negligible
circularcross sectionplaced onemetreapart in avacuum
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITmol (SI unit of
amount of substance)Amount of substance that contains as many
elementary entities as there are number of atoms in 0.012 kg of
C-12(Which is equal to 6.023*1023 ---> Avogadro number)
Elementary entities one word used for electrons, protons, atoms,
molecules etc.
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITcandela ( SI unit of
Luminous Intensity)1 candela is luminous intensity in a given
direction of a source that emits monochromatic radiations of
frequency 540* 1012 Hz and that has radiant intensity of 1/683
W/str in that direction.
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITradian (SI unit of
plane angle)1 radian is angle subtended at the centre of a circle
by an arc equal in length to radius of the circle.
DEFINITIONS OF BASIC and SUPPLEMENTARY UNITsteradian ( SI unit
of solid angle i.e. angle in space )1 steradian is defined as solid
angle subtended at the centre of a sphere, by that surface of the
sphere, which is equal in area, to the square of radius of the
sphere.
= surface area / r2
PREFIXESPhysical quantities whose magnitude is either too large
or too small, can be expressed more compactly by using certain
prefixes
Power of 10 PrefixSymbolPower of 10 PrefixSymbol101decada101
decid102hectoh102centic103kilok103 millim106megaM106
micro109gigaG109 nanon1012teraT1012picop1015petaP1015
femtof1018exaE1018attoa
Practice Questions
Ques : Write below with values using prefix1.6* 1012 m =
_____________ Pm0.876 * 10 -5m = ____________mm3.5*10-7s =
_____________s480 * 10-11m = ____________nmQues : What is
difference between Nm, nm and Mm ?
Practical UnitsApart from fundamental and derived units we also
use very frequently practical unitsPractical units of length
Practical units of Area
Practical units of Mass
Practical units of Time Macroscopic unitsMicroscopic unitsUsed
to measure large amount of physical quantity Used to measure very
small amount of physical quantity Practical units of
LENGTHMacroscopic
Microscopic Units Astronomical unit ( AU)Light year (ly)Parsec (
Parallactic Second)Micron Angstrom FermiPractical units of
lengthAstronomical unit ( AU)Mean distance between centre of the
sun and centre of the earth
Average distance between sun and earth is 1.496 x 1011 m1 AU =
1.496 x 1011 m
Practical units of lengthLight Year (ly)Distance travelled by a
ray of light in 1 year in vacuumIt is equal to 9.46 x 1015 m
Practical units of lengthParsec (parallactic second) Distance at
which arc of length 1 AU subtends angle of 1s of arc
Practical units of length
