Physics - Fluid Question with Solution | TestHub

The upward force due to surface tension is given by $F=T\times C\times \cos \theta$, where $C$ is the inner circumference of the capillary tube.

For water, the angle of contact $\theta =0^{\circ }$, so $\cos \theta =1$.

Given $F=105\text{ dyne}=105\times 10^{-5}\text{ N}$ and $T=7\times 10^{-2}\text{ N/m}$.

Substituting the values:

$105\times 10^{-5}=7\times 10^{-2}\times C$

$C=\frac{105\times 10^{-5}}{7\times 10^{-2}}$

$C=15\times 10^{-3}\text{ m}$

$C=1.5\times 10^{-2}\text{ m}=1.5\text{ cm}$

Answer: $1.5\mathrm{cm}$