Question

When a glass capillary tube of the radius $0.015\,cm$ is dipped in water, the water rises to a height of $15\,cm$ within it. Assuming the contact angle between water and glass to be $0^\circ $ , the surface tension of water is $\left[\right.\rho _{\text{water }}=1000 \, kg \, m^{- 3}, \, g=9.81 \, ms^{- 2}\left]\right.$

• A. $0.11 \, N \, m^{- 1}$
• B. $0.7 \, N \, m^{- 1}$
• C. $0.072 \, N \, m^{- 1}$
• D. None of these

Answer 1

Answer: (A)

From capillary tube experiment, we know that
$2\pi r\times T \, \cos\theta =\pi r^{2}h\rho g$
$\Rightarrow \, \, T=\frac{r h \rho g}{2}=0.11 \, N \, m^{- 1}$