Surface Energy & Work done in blowing liquid drop_Surface Tension(Part-IV)|Class 11th & 12th Physic

Описание

Surface Energy
The potential energy per unit area of liquid surface under isothermal conditions is called surface energy per unit area.
The molecule well within the liquid is surrounded by similar liquid molecules from all sides and hence there is no resultant force on it. On the other the hand a molecule within the surface film is surrounded by liquid molecules only on one side of the surface while on other side it may be surrounded by air molecules or vapor of the liquid, the density of which is much less as compared to density of liquid molecules. Thus, there is a resultant inward force on a molecule in the surface film. This force tries to pull the liquid molecule into liquid.
Consider a rectangular frame of wire ABCD ON WHICH WIRE CD can slide without friction. Suppose this film is dipped in soap solution, taken outside horizontally. Then a film of soap solution will be formed in the frame. If l is length of wire CD and T is surface tension of soap solution then wire CD experiences a net resultant inward force F=2tl.
Due to this inward force the film will move towards side AB to decrease the surface area.
To increase the surface area of soap film, imagine that external force F’ equal & opposite to F is applied to side CD SO THAT CD moves to C’D’ through small distance dx.
The work done in this process is stored as potential energy in to the soap film which is also called as surface energy.