A) \[{{r}_{2}}-{{r}_{1}}\]
B) \[\sqrt{r_{1}^{2}-r_{2}^{2}}\]
C) \[\frac{{{r}_{1}}+{{r}_{2}}}{2}\]
D) \[\frac{{{r}_{1}}{{r}_{2}}}{{{r}_{2}}-{{r}_{1}}}\]
Correct Answer: D
Solution :
If R be the radius of the interface, then \[\frac{4T}{r}=\frac{4T}{{{r}_{1}}}-\frac{4T}{{{r}_{2}}}\] or \[\frac{1}{r}=\frac{1}{{{r}_{1}}}-\frac{1}{{{r}_{2}}}\] \[=\frac{{{r}_{2}}-{{r}_{1}}}{{{r}_{1}}{{r}_{2}}}\] So, \[r=\frac{{{r}_{1}}{{r}_{2}}}{{{r}_{2}}-{{r}_{1}}}\]
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