SURFACE TENSION

SURFACE TENSION. 

                         Surface tension is defined as the tensile force acting on the surface of a liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension. The magnitude of this force per unit length of the free surface will have the same value as the surface energy per unit area. It is denoteby Greek letter 𝛔 (called sigma) . In MKS units, it is expressed as kgf/m while in SI units as N/M.

SURFACE TENSION

               The phenomenon of surface tension is explained by above Figure. Consider three molecules of A, B, C of a liquid in a mass of liquid. The molecule A is attracted in all directions equally by the surrounding molecules of the liquid. Thus the resultant force acting on the molecule A is zero . But the molecule B, which is situated near the free surface, is acted upon by upward and downward forces which are unbalanced. Thus a net resultant force on molecule B is acting in downward direction. The molecule C situated on the free surface of the liquid does experience a resultant downward force. Thus the free surface of the liquid acts like a very thin film under tension of the surface of the liquid acts as though it is an elastic membrane under tension. 

SURFACE TENSION ON LIQID DROPLET.

                               Consider a small spherical droplet of a liquid of radius ‘r’ . On the entire surface of droplet, the tensile due to surface tension will be acting. 
   Let 𝛔 = Surface tension of the liquid
           p = Pressure intensity inside the droplet (in excess of the outside pressure intensity)
           d = Dia. of the droplet.

SURFACE TENSION ON LIQUID DROPLET

                                        The End. 

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