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