Height of atmosphere
For calculating the height of atmosphere, we make use of the following assumptions:
(i) The value of g does not change appreciably up to a certain height.
(ii) Temperature remains uniform throughout.
(iii) Although density of air decreases with height, we assume it to be uniform and take ρ =1.3 kg m-3.
Pressure exerted by h height of air column = Pressure exerted by 0.76 m of Hg
or h ρ g = 1.013 × 105 Pa
or h = 1.013 × 105 Pa / (1.3 x 9.8) = 7951 m = 8 km.
In actual practice, both the density of air and the value of g decrease with height, so the atmospheric cover extends with decreasing pressure even beyond 100 km.