Explain Surface tension and surface Energy.

Surface Tension (T) : The force per unit length on an imaginary line, drawn on the free surface of a liquid is called surface tension

$\mathrm{T}=\frac{\mathrm{F}}{\mathrm{l}}=\text{ Units }:{\mathrm{Nm}}^{-1}$

Surface energy : The excess potential energy per unit area of the surface film is called surface energy. 

SI Units J/m².

Relation between surface energy and surface tension :

Consider a liquid film formed across ABCD, AB is movable wire, liquid film possesses two surfaces.

T is the surface tension.

Force of surface tension acting on the movable wire

${ }^{\text{'}}\mathrm{\Delta x} \text{'}$displacement moved

Small work is done
$\begin{array}{l}\mathrm{W}=\text{ F.S. }\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\left(\mathrm{T}=\frac{\mathrm{F}}{2\mathrm{L}}\right)\\ \mathrm{W}=2\mathrm{TL}.\mathrm{\Delta x}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em} (\mathrm{F}=2\mathrm{TL})\\ \mathrm{W}=2\mathrm{T\Delta A}\hspace{0.25em} \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\Rightarrow \mathrm{T}=\frac{\mathrm{W}}{\mathrm{A}}\end{array}$

Surface tension numerically equal to surface energy per unit area.