Water rises to a height of 6.6cm in a a capillary tube of radius 0.2mm. The surface tension of water is (g = 10ms^-2)

Given,

$\mathrm{h}=6.6\times {10}^{-2}, \mathrm{r}=0.2\times {10}^{-3}, \mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2$

we know that surface tension,

$\mathrm{T}=\frac{\mathrm{\rho ghr}}{2}$

$$\begin{gathered} =\frac{{10}^3\times 6.6\times {10}^{-2}\times \left(10\times 0.2\times {10}^{-3}\right)}{2} \\ =6.5\times {10}^{-2}\mathrm{N}/\mathrm{m} \end{gathered}$$

Hence the correct answer is $6.5\times {10}^{-2}\mathrm{N}/\mathrm{m}.$