Question

Surface energy is ________________

(a) kinetic energy of the surface molecules

(b) the force per unit length acting on surface particles

(c) the energy of the molecules inside the beaker

(d) the extra energy that the molecules at the surface have relative to molecules inside the liquid

This question was posed to me in semester exam.

The origin of the question is Fluids Mechanical Properties topic in section Mechanical Properties of Fluids of Physics – Class 11

Answer 1

Right choice is (d) the extra energy that the molecules at the surface have relative to molecules inside the liquid

To explain I would say: Molecules much below the surface are attracted by equal forces in all directions, while molecules on the surface have a net force acting on them as they are exposed to air from one side and water on another. This net force acting on the surface molecules has a corresponding energy called surface energy.