A method for determining the surface tension of a liquid is to find the force ne

Question

A method for determining the surface tension of a liquid is to find the force needed to pull a wire ring from the surface of a liquid. For this purpose, usually platinum rings are used, since they form zero contact angles with the outermost and innermost peripheries of the wire. Determine the force required to pull such a ring of diameter 0.4 m from water above the weight of the wire. Assume that the diameter of the platinum wire is very small when compared with the diameter of the ring. The surface tension for water in the presence of air is 0.073 N/m. (Ans. 0.1835 N)

Explanation / Answer

Force required to pull a circular ring of radius r from the surface of water of surface tension T is F=4rT
=>Force F=4x(0.4/2)x0.073       given diametre = 0.4,=>radius=0.2 
=>F=0.1835N

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