Question

Derive an expression for excess pressure (i) inside a liquid drop (ii) inside
a soap bubble.​

Answer 1

Consider a Radius R and Surface Tension T soap bubble. Two free soap bubble surfaces emerge. The molecules on the surface film experience the net force in the inward direction normal to the material as a result of surface tension. Therefore, inside, there is more pressure than outside.  

P = pi - po  

The yield point of the drop will experience the net force in the area extending along with excessive stress inside of the liquid drop, due to which the drop will expand.