Special Units



Special Units

1. Length:

  • Micron(\mu )= 10^{-6}m = 10^{-4} cm
  • Angstrom (A) = 10^{-10}m = 10^{-8}cm
  • Fermi = 10^{-15}m = 10^{-13}cm
  • Astronomical Unit (A.U) = (1.5) 10^{11}m  = (1.5) 10^{13}cm;                                                                                                    
     
  • What is 1 A.U. ?                                                                                                                                                                                                                                Ans: 1 A.U(Astronomical Unit) is the distance between Earth and Sun. 1A.U=(1.496) 10^{8}km.
  • X ray unit (X.U) = 10^{-13}m (wave length of X-Rays)
  • Light year = Distance traveled by light in one year= 9.5\times 10^{15}m =9.5\times 10^{12}km
  • parsec = 3.26 light years = 3.1\times 10^{16}m
  • 1 mile = 1.609 km = 8 furlongs = 1760 yards = 5280 feet
  • 1 agate(typography) = 0.07 inch = 1.8 centimeter
  • 1 angstrom = 0.0000001 mm = 0.000000004 inch
  • 1 cable’s length = 720 feet = 219.46 meters
  • 1 chain (engineer’s) = 100 feet = 30.48 meters
  • 1 chain (Gunter’s or surveyor’s) = 66 feet = 20.12 meters
  • 1 cubit = 18 inches = 45.72 centimeter
  • 1 degree (geographical) = 69.05 miles = 111.12 kilometers
  • 1 decametre = 10 meters = 32.81 feet
  • 1 fathom = 6 feet = 1.83 meters
  • 1 hand = 4 inches = 10.16 centimeters
  • 1 league = 3 miles = 4.83 kilometers
  • 1 link (engineer’s) = 1 foot = 0.31 meter
  • 1 link (gunter’s or surveyor’s ) = 7.92 inches = 10.16 centimeters
  • 1 perch or pole = 16.5 feet = 5 meters
  • 1 point (typography ) = 0.1 inch = 0.35 millimeter

2.Time :

  • Solar day def: The time taken by earth to complete one rotation about its own axis with respect to sun is called solar day. (Avarage value for all the days of one year is Mean solar day).
  • Siderial day : It is 4.1min shorter than Mean solar day .
  • siderial year :365.26 Mean solar day  d ) Solar year = 365.24 Mean solar day
  • Lear year = The year in which February month has 29 days is called leap year.It is divisible by 4.
  • Lunar month :Time taken by moon to complete one rotation around earth is lunar month = 27.3 days.

3. Mass :

  • Atomic mass Unit ( a.m.u) : = \frac{1}{12}of mass of  C_{12}  atom =\frac{1}{12}\times\frac{12}{N} = \frac{1}{6.023\times10^{23}} gr = 1.67\times10^{-24}gr = 1.67\times10^{-27}kg.
  • 1 assay ton = 29.167 grams = 1.03 ounces
  • 1 carat = 200 milligrams = 3.09 grains
  • 1 decigram = 100 milligrams = 1.54 grains
  • 1 decagram = 10 grams = 0.35 ounce
  • 1 pound = 0.45 kilograms

4.Pressure :

  • Atmosphere =760 mmHg = 76\times13.6\times980 dyne/cm^{2} = 1.013\times10^6 dyne/cm^{2} = 1.013\times10^5 N/m^{2}or pa.
  • Bar = 750 mmHg = 75\times13.6\times980 dyne/cm^{2}=10^6 dyne/cm^{2} = 10^5 N/m^{2}or pa.
  • Torr =1 mm Hg =0.1\times13.6\times980 dyne/cm^{2}=1333 dyne/cm^{2}=133N/m^{2} or pa.

5.Area :

  • Barn: this is unit of area,it is used to measure cross section of nuclei.
  • Barn =10^{-28} m^{2}
  • 1 acre = 4047 sq meters = 4840 sq yards = 43560 sq ft
  • 1 are = 100 square meters = 1076.39 sq feet
  • 1 square(building) = 100 sq feet = 9.29 sq meters
  • 1 sq link = 62.73 sq inches = 404.69 sq cm
  • 1 township = 36 sq miles = 93.24 sq kms

6. Wind Speeds :

  • light wind = 7 miles/hr
  • light breeze = 11 miles/hr
  • gentle breeze = 16 miles/hr
  • moderate breeze = 20 miles/hr
  • fresh breeze = 25 miles/hr
  • strong breeze = 30 miles/hr
  • moderate gale = 35 miles/hr
  • fresh gale =45 miles/hr
  • strong gale = 50 miles/hr
  • whole gale = 60 miles/hr
  • storm = 70 miles/hr
  • hurricane = 80 miles/hr

7.Horse Power : It is the British Unit of power =746 w.
8.Special units of derived Physical Quantities:

S.NOPhysical QuantityC.G.S UnitS.I Unit
1ForceDyneNewton
2Work , EnergyErgJoule
3PowerWatt
4PressurePascal
5


Multiples,sub multiples of units.

Multiples and sub multiples of Units in S.I system :
Depending upon the magnitudes of physical quantities we measure, we have to use different multiplication factors suitable for that particular case.Here let us see some widely used multiplication factors.

Multiplication FactorPrefixsymbol
10^{-1}decid
10^{-2}centic
10^{-3}millim
10^{-6}micro\mu
10^{-9}nanon
10^{-12}
picop
10^{-15}femtof
10^{1}
decada
10^{2}
hectah
10^{3}
kiloK
10^{6}
megaM
10^{9}gigaG
10^{12}
teraT
10^{15}
petaP

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