From a water tap, liquid comes out in from of cylinder. As water moves down, radius of that cylinder decreases. Consider, a very small element of height h and and radius R (due to smell height radius is assumed to be constant)

This element is given in the diagram. An imaginary cross-section ABCD divides this element in two equal semi cylinder. S is surface tensionof liquid. Now choose correct statement(s)

Options

A. Surface energy of this elementary cylinder is `S[2piRh+2piR^(2)]`
B. Pressure inside the cylinder is more than atmospheric pressure by` (2S)/(R )`
C. Force exerted by one half cylinder on another half cylinder due to surface tension is 2Sh.
D. Surface energy of this elementary cylinder is `Sxx2piRh`

Answer

C, D

Explanation

`"Surface energy" = "free surface area" xx "surface tension"`
for a cylindrical surface excess pressure is `(S)/(R )`