Surface tension

Surface Tension:

Surface tension is defined as the tensile force acting on the surface of a liquid is contact with a gas or on the surface behaves like a membrane under tension. The magnitude of thisforce per unit length of free surface will have the same value as the surface energy per unit
area. It is denoted by 𝜍 (sigma). 

Units of surface tension:

 MKS units: Kg f/m
SI units:  N/m

Surface Tension on Liquid Droplet: 

When Consider a small spherical droplet of a liquid of radius ‘r’ on the entire surface of the droplet, the tensile force due to surface tension will be acting
Let σ = surface tension of the liquid
p= pressure intensity inside the droplet (In excess of outside pressure intensity)
d= Diameter of droplet
Let, the droplet is cut in to two halves. The forces acting on one half (say left half) will be

i) Due to surface tension acting around the circumference of the cut portion there is a tensile force present onit.
= σ ×circumference = σ × 𝜋d
ii) Pressure force on the area.

The above  two forces will be equal and opposite under equilibrium conditions.

Surface Tension on a Hallow Bubble at Air: 

When we consider a hallows bubble like soap is in air, This bubble has two surfaces in contact with air, one is inside and other one is at outside. Thus, two surfaces are subjected to surface tension.