Special Length units Unit name Unit Symbol Value in meters
fermi f 10 -15 m
angstrom Å 10 -10 m
astronomical |
|
|
unit ( average distance |
|
|
of sun from earth ) |
AU |
1.496 X 10 11 m |
light year ( distance travelled by light in 1 year with velocity 3 X 10 8 m / s ) |
ly |
9.46 X 10 11 m |
parsec ( distance at which average radius of earth ’ s orbits subtends an angle of 1 arc second ) |
pc |
3.08 x 10 16 m |
Measurement of Mass
Mass is usually measured in terms of kg but for atoms and molecules , unified atomic mass unit ( u ) is used .
1 u = 1 / 12 of the mass of an atom of carbon-12 isotope including mass of electrons ( 1.66 x 10 -27 kg )
Apart from using balances for normal weights , mass of planets is measured using gravitational methods and mass of atomic particles are measured using mass spectrograph ( radius of trajectory is proportional to mass of charged particle moving in uniform electric and magnetic field ).