Question:
When two soap bubbles of radii a and $\mathrm{b}(\mathrm{b}>\mathrm{a})$ coalesce, the radius of curvature of common surface is :
Correct Option: 1
Solution:
(1)
Excess pressure at common surface is given by
$P_{e x}=4 T\left(\frac{1}{a}-\frac{1}{b}\right)=\frac{4 T}{r}$
$\therefore \frac{1}{\mathrm{r}}=\frac{1}{\mathrm{a}}-\frac{1}{\mathrm{~b}}$
$r=\frac{a b}{b-a}$