# What pressure to take in surface tension question?

Pressure inside a water droplet is $0.32 N/cm^2$ if surface tension of liquid is $0.095 N/m$. We have to find the radius of the bubble

since it's a water droplet the formula used is $$P_i-P_o=\frac{2T}{R}$$ The $P_i$ is internal pressure wehreas $P_0$ is external pressure so the $P_0$ should be taken in consideration but the solution of the question directly puts $0.32$ in place of pressure difference. where I am doing wrong in the question.

• How does 0.32 N/cm2 compare to atmospheric pressure? Sep 17 '18 at 12:55
• @JeffreyJWeimer sorry - you and me both mate! Sep 17 '18 at 12:56
• @Wasabi answer is already in the question, OP just needed a pointer not a 5 page essay. Sep 17 '18 at 14:45

Have you considered that the solution is assuming that the pressure is gauge pressure ie above atmospheric...

So that means if you have the bubble pressure as an absolute pressure reading and you subtract the external atmospheric pressure you end up with the difference which is the value given in the solution.