A to Z of Physics: Special Units Of Physical Quantities.

Monday, December 29, 2008

Special Units Of Physical Quantities.

1. Length: a) Micron( $\mu$ )= $10^{-6}$ m = $10^{-4}$ cm

b) Angstrom (A) = $10^{-10}$ m = $10^{-8}$ cm

c) Fermi = $10^{-15}$ m = $10^{-13}$ cm

d)Astronomical Unit (A.U) = 1.5 $10^{11}$ m = 1.5 $10^{13}$ cm

e)X ray unit (X.U) = $10^{-13}$ m (wave length of X-Rays)

f) Light year = Distance traveled by light in one year= $9.5\times 10^{15}$ m = $9.5\times 10^{12}$ km

g ) parsec = 3.26 light years = $3.1\times 10^{16}$ m

2.Time :

a ) Solar day def: The time taken by earth to complete one rotation about its own axis with respect to sun is called solar day. ( Average value for all the days of one year is Mean solar day).

b)Siderial day : It is 4.1min shorter than Mean solar day .

c )siderial year :365.26 Mean solar day d ) Solar year = 365.24 Mean solar day

e )Lear year = The year in which February month has 29 days is called leap year.It is divisible by 4.

f)Lunar month :Time taken by moon to complete one rotation around earth is lunar month = 27.3 days.

3. Mass : a ) 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.

4.Pressure : a ) 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.