Principle and Working:
Surface tension for water is determined using ring-pull out method. The experiment utilizes a dynamo meter on which a metal ring is suspended, which can be lowered or pulled out of water.
In the present setup, a metal ring is completely immersed in the liquid, so that the entire surface is wetted. The ring is than slowly pulled out of the liquid, drawing a thin sheet of liquid behind it. The liquid sheet tears when the tensile force exceeds a limit value,
F=σ 4πR,
where
R = Ring edge radius
σ = Surface tension of liquid.
