When a long glass capillary tube of radius $0.015 \mathrm{~cm}$ is dipped in a liquid, the liquid rises to a height of $15 \mathrm{~cm}$ within it. If the contact angle between the liquid and glass to close to $0^{\circ}$, the surface tension of the liquid, in millinewton $\mathrm{m}^{-1}$, is $\left[\rho_{\text {(liquid) }}=900 \mathrm{kgm}^{-3}, \mathrm{~g}=10 \mathrm{~ms}^{-2}\right]$ (Give answer in closest integer)
Capillary rise
$\mathrm{h}=\frac{2 \mathrm{~S} \cos \theta}{\rho g r}$
$\mathrm{S}=\frac{\rho g r h}{2 \cos \theta}$
$=\frac{(900)(10)\left(15 \times 10^{-5}\right)\left(15 \times 10^{-2}\right)}{2}$
$\mathrm{S}=1012.5 \times 10^{-4}$
$\mathrm{S}=101.25 \times 10^{-3}=101.25 \mathrm{mN} / \mathrm{m}$
In question closest integer is asked
so closest integer $=101.00 \mathrm{Ans}$.
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