Question
When two soap bubbles stay in contact, what is the radius of the interface?
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Answer
If r1 and r2 are the radii of the soap bubbles, the net excess pressure at the interface is,
$\frac{4\sigma}{\text{r}_{\text{eq}}}=\frac{4\sigma}{\text{r}_1}-\frac{4\sigma}{\text{r}_2}$
$\therefore\frac{1}{\text{r}_\text{eq}}=\frac{1}{\text{r}_1}-\frac{1}{\text{r}_2}$
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