Test: Surface Tension

When liquid molecules are attracted strongly to themselves and weakly to those of solids, it costs lots of energy to create liquid-solid surface and liquid then does not wet the solid.
For Example: Mercury molecules (which make an obtuse angle with glass) have a strong force of attraction between themselves and a weak force of attraction toward solids. Hence, they tend to form drops. 
On the other hand, water molecules make acute angles with glass. They have a weak force of attraction between themselves and a strong force of attraction toward solids. Hence, they tend to spread out.

Work done=total surface x Surface tension
=2x4πr²xσ
=2x4x3.14(0.03)²x 0.05
=1.1x10^-3J

The property by virtue of which the free surface of a liquid at rest behaves like an elastic stretched membrane tending to contract so as to occupy minimum surface area is known as surface tension. By the definition of surface tension.

Force due to surface tension acts all along the circumference of the circular plate. Therefore, force required to take away of plate is,
F = T x 2πr = 70 x 2 x 3.14 x 4 = 1758.4 dyne/cm
 

When liquid molecules are attracted strongly to themselves and weakly to those of solids, it costs lots of energy to create liquid-solid surface and liquid then does not wet the solid.

For Example: Mercury molecules (which make an obtuse angle with glass) have a strong force of attraction between themselves and a weak force of attraction toward solids. Hence, they tend to form drops.
On the other hand, water molecules make acute angles with glass. They have a weak force of attraction between themselves and a strong force of attraction toward solids. Hence, they tend to spread out.

When wetting agents like soap or dyes are added to water, the angle of contact becomes small. This happens so that the particles penetrate well and become effective.

NaCl salts cause an increase of the surface tension and the residence time of interfacial water molecules.

From the concept of surface tension; pressure inside the bubble = 4S/R.

The force acting on this line is proportional to the length of this line. If l is the length of imaginary line and F the total force on either side of the line then,
F∝l
⇒ F=Sl
Or, surface tension, S=force/length
From this expression, Surface tension can be defined as the force acting per unit length of an imaginary line drawn on the liquid surface, the direction of force being perpendicular to this line and tangential to the liquid surface.it is denoted by S and it is a scalar quantity. 

When a liquid surface meets a solid surface the angle (φ) between the two surfaces is important. In fact a surface will be wetted by water if the angle of contact is less than 90^o, and so waterproofing is designed to produce an angle of contact that is greater than 90^o.