Definitions [5]
Define the angle of contact for a given pair of solid and liquid.
The angle between tangents drawn at the point of contact to the liquid surface and the solid surface inside the liquid is called the angle of contact for a pair of solid and liquid. It is denoted by θ.
Define the surface tension of a liquid.
Surface tension is defined as the force acting on a unit length of an imaginary line drawn on the free surface of the liquid, the direction of the force being perpendicular to the line so drawn and acting parallel to the surface.
Define angle of contact.
When a liquid is in contact with a solid, the angle between the tangent drawn to the free surface of the liquid and the surface of solid at the point of contact measured inside the liquid is called the angle of contact.
Define surface tension.
Surface tension is defined as the force per unit length acting at right angles to an imaginary line drawn on the free surface of the liquid.
Define the surface energy of the liquid.
The potential energy is greater for molecules at the surface film as compared to molecules well inside the liquid. This extra energy of the molecule on the surface layer of a liquid is called the surface energy of the liquid.
Theorems and Laws [1]
Prove that, equivalent S.I. unit of surface tension is J/m2.
T = `F/L`
where F = Force (N), L = Length (m)
= SI unit of T = `N/m`
Surface tension can also be written as
T = `W/A`
where W = Work (J), A = Area (m2)
= SI unit of T = `J/m^2`
We know
1J=1N×1m
So,
`J/m^2 = (N * m)/m^2 = N/m`
Both units are the same
`1N/m equiv 1J/m^2`
