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).