Question

{ " মানে কি ?)
3- How
How surface tension is related with surface
energy? (পৃষ্ঠটানে পৃষ্ঠশক্তিৰ লগত কিদৰে জড়িত?)​

Answer 1

The surface energy per unit area of a liquid is equal to its surface tension.

Let T be the surface tension of soap solution and l, the length of wire PQ in contact with the soap film. As such surface exerts a force Tl, the total force on the wire is 2Tl. Suppose the wire PQ is pulled outward very slowly through a distance dx.

W=  force × displacement

∴   W = Fd x= 2TldxW = Fdx = 2Tldx

As the film has two surfaces, the increase in its surface area is

        A= 2ldx

Thus, the work done per unit surface area is

W/A= 2Tldx / 2ldx = T

W/A=T

This  is called the surface energy.