Derive an expression for the excess pressure inside a liquid drop.
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Solution
Suppose that ABC is a half drop of a liquid, whose radius is r and surface tension is T. On the molecules of liquid towards the spart, the cohesive force F1 would be downwards.
Suppose, excess pressure is P which acts upwards
therefore Upwards force F2=PA=Pπr2
∴ For the equilibrium of the liquid drop F1=F2
2πrT=Pπr2
P=2Tr
Thus, the pressure inside the drop 2Tr more than the pressure outside the drop.