When a vertical capillary of length `l` with a sealed upper end was brought in contact with the surface of a liquid, the level of this liquid rose to the height `h`. The liquid density is `rho`, the inside diameter the capillary is `d`, the contact angle is `theta`, the atmospheric pressure is `rho_(0)`. Find the surface tension of the liquid. (Temperature in this process remains constant.)

Explanation

We have by Boyle's law
`(p_0 - rho gh + (4 alpha cos theta)/(d)) (l - h) = p_0 l`
or, `(4 alpha cos theta)/(d) = rho gh + (p_0 h)/(1 - h)`
Hence, `alpha = (rho gh + (p_0 h)/(l - h))(d)/(4 cos theta)`.