Question

Draw a well labelled diagram to show that the angle of contract for kerosene with glass is Acute​

Answer 1

Explanation:

since the kerosene doesn't wet the glass completely

It makes an acute angle at glass-kerosene interface

Answer 2

For a liquid that partially wets the solid e.g., kerosene in contact with the glass. The adhesive force is very large compare to the cohesive force $(\mathrm{PC}<\sqrt{2} \mathrm{P} \mathrm{A})$ Therefore their resultant is directed into the solid, The free surface of a liquid at rest is always perpendicular to the resultant force on it.

Therefore, liquid molecules like P move upward till the liquid surface in contact becomes perpendicular to The liquid surface thus acquires a concave shape and the tangent to the makes an acute angle of contact, with the surface of solid, see fig.

For a non-wetting liquid (e.g. mercury in contact with glass) the cohesive force is very large compared to the adhesive force $(\mathrm{PC}>\sqrt{2} \mathrm{P} \mathrm{A})$Therefore, their resultant points are into the liquid.

Hence the liquid surface curves down acquiring a convex shape until it becomes perpendicular to The tangent to it makes an obtuse angle of contact with the surface of the solid. See fig.