Q19 of 24 Page 75

If a drop of liquid breaks into smaller droplets, it results in lowering of temperature of the droplets. Let a drop of radius R, break into N small droplets each of radius r. Estimate the drop-in temperature.

Here, N droplets form a bigger drop.


So, volume of bigger drop = sum of the volumes of the smaller drops.





Now, energy released is equal to the difference in the surface energies.



Now, if is the temperature drop, m is the mass and c is the specific heat then,




is negative as R>r.


Hence, the drop-in temperature is,


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(a) Pressure decreases as one ascends the atmosphere. If the density of air is ρ, what is the change in pressure dp over a differential height dh?


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