Aiims exam question

Two soap bubbles have radii in the ratio 2 : 1. What is the ratio of excess pressure inside them?

Your Answer


Excess pressure inside a bubble of radius R and surface tension T is given by $P_e\:=\:\frac{4T}{R}$.
Therefore excess pressure is inversely proportional to the radius.
So $\frac{P_1}{P_2}\:=\:\frac{R_2}{R_1}\:=\:\frac{1}{2}$.
So the ratio of excess pressure inside them will be 1:2.