Some Units and Definitions
Some Definitions and Units
(1) Length :
(i) 1 fermi = 1 fm = 10–15m
(ii) 1 angstrom = 1Å = 10–10m = 10–8cm = 10–7mm = 0.1 mmm
(iii) 1 micron = mm = 10–6m
(iv) 1 astronomical unit = 1 A.U. = 1. 49 * 1011m ≈ 1.5 * 1011m ≈ 108km
(v) 1 Light year = 1 ly = 9.46 x 1015m
(vi) 1 Parsec = 1pc = 3.26 light year
(2) Mass :
(i) Metric tonne : 1 Metric tonne = 1000 kg
(ii) Quintal : 1 Quintal = 100 kg
(iii) Atomic mass unit (amu) : 1 amu = 1.67 x 10–27kg
(3) Time :
(i) Year : It is the time taken by earth to complete 1 revolution around the sun in its orbit.
(ii) Lunar month : It is the time taken by moon to complete 1 revolution around the earth in its orbit.
1 Lunar month = 27.3 days
(iii) Solar day : It is the time taken by earth to complete one rotation about its axis with respect to sun.
1 Solar year = 365.25 average solar day
average solar day 1/365.25 the part of solar year
(iv) Sedrial day : It is the time taken by earth to complete one rotation about its axis with respect to a distant star.
1 Solar year = 366.25 Sedrial day = 365.25 average solar day
Thus 1 Sedrial day is less than 1 solar day.