Question

Expression for relation between gauge pressure inside a droplet and surface tension

Answer 1

It is because of surface tension that pressure of a liquid increases within a bubble. Consider the free-body diagram of a bubble as shown in Fig.1.8. If the force due to surface tension at the edge is balanced by the pressure force inside the bubble, we have

$\displaystyle 2\pi R \sigma = p \pi R^2$ (1.24)

i.e.,

$\displaystyle p = {{2 \sigma} \over {R}} $

where p is the pressure difference between inside the drop and that outside. In addition the pressure inside the bubble is greater than that outside.