Two bubbles of radii 2mm and 3mm when touch each other, the radius of curvature of their interface is

Given,

$$\begin{gathered} {\mathrm{R}}_1=2\mathrm{mm} \\ {\mathrm{R}}_2=3\mathrm{mm} \end{gathered}$$

at the contact surface pressure difference is 

$\mathrm{P}=\frac{4\mathrm{T}}{{\mathrm{R}}_1}-\frac{4\mathrm{T}}{{\mathrm{R}}_2}=\frac{4\mathrm{T}}{\mathrm{R}}$

$\mathrm{R}=\frac{{\mathrm{R}}_1{\mathrm{R}}_2}{{\mathrm{R}}_1-{\mathrm{R}}_2}=\frac{2\times 3}{3-2}=6\mathrm{mm}$