Q 11-09-041JEE MainJEE Main 2025 (22 Jan, Shift 1)Easy
Two soap bubbles of radius $2\ \text{cm}$ and $4\ \text{cm}$, respectively, are in contact with each other. The radius of curvature of the common surface, in cm, is ______.
Numerical value type. Enter your answer.
Answer: 4
Excess pressure inside a soap bubble is $4T/r$. The common film must balance the difference of the two excess pressures:
$$\frac{4T}{r} = \frac{4T}{r_1} - \frac{4T}{r_2} \Rightarrow r = \frac{r_1r_2}{r_2-r_1}$$
$$r = \frac{2\times4}{4-2} = 4\ \text{cm}$$
Solution by Sreeraj P, M.Sc Physics