Question
Explain why.
There is no atmosphere on moon.
There is no atmosphere on moon.
✓
Answer
As acceleration due to gravity on moon is 1/6th of g on earth. So the escape velocity on moon $\text{V}_{\text{es}}=\sqrt{2\text{gR}}=2.38\text{km}/\text{s}$ M = Mass of hydrogen, As H2 is lightest gas m = 1.67 × 10-24kg
$\text{v}_\text{rms}=\sqrt{\frac{3\text{K}_\text{B}\text{T}}{\text{m}}}=\sqrt{\frac{3\times1.38\times10^{-23}\times300}{1.67\times10^{-24}}}$
= 2.72 km/s Due to small gravitational force and vrms is greater than escape velocity so molecule of air can escape out. As the distance of moon from sun is approximately equal to that of earth so the intensity of energy of sun reaches to moon is larger due to lower density of atmosphere, distance become smaller than earth when moon is towards sun during its rotation around earth. Due to this (sun light), rms speed of molecule increase and some of them can speed up more than escape velocity and so probability of escaping out increased. Hence over a long time moon has lost most of its atmosphere.Need a full question paper?
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