Question

A capillary tube with an inside radius of 638 𝑛𝑚 can support a 100 𝑚𝑚 column of liquid that has a density of 820 𝑘𝑔𝑚−3 . The observed contact angle is 12.5°. Find the surface tension of the liquid for ℎ = 20 𝑐𝑚. 

Answer 1

Determine the surface tension:

$$h=\frac{2\sigma\cos\theta}{\rho gr},\\\space\\ \sigma=\frac{\rho grh}{2\cos\theta},\\\space\\ \sigma=\frac{820·9.8·638·10^{-9}·0.2}{2\cos12.5}=5.25·10^{-4}\text{ N/m}.$$