Question

The surface tension of a liquid is $5$ Newton per meter. If a film of this liquid is held on a ring of $0.02\,meter{s^2}$. Its surface energy is about:
A) $5\,J$

B) $2\,J$

C) $0.2\,J$

D) $3\,J$

Answer 1

Here we have to apply the concept and formula of surface energy to get the answer.

Surface energy maximizes the destruction of intermolecular bonds that happens as the surface is formed. It is also referred to as the surface free energy. In basic terms, surface energy is defined as the work per unit area performed by the force that produces a new surface.

Complete step by step solution:
Given,
Surface tension, $T = 5\,N{m^{ - 1}}$

Area, $A = 0.02\,{m^2}$

Since there are two sides of a ring, so
Area $= 2A$

The surface energy is mathematically given by:
Surface energy $=$ surface tension $\times$ surface area
$E = T \times 2A \\\ = 5 \times 2 \times 0.02 \\\ = 0.2\,J \\\$

Hence, the correct answer is option B.

Additional information:
Surface tension: Surface tension is the ability of liquid surfaces to shrink to the lowest possible surface area. Surface tension allows objects, typically denser than water to float on the surface of water.

Cohesive forces between molecules in a liquid are shared with all adjacent molecules. Surface tension may be described as the property of the surface of a liquid which due to the coherent nature of the water molecules allows it to resist external force.
Surface tension defines the quality of the composition of the detergent. The high surface tension of the water renders it a relatively weak cleaning agent. By increasing the temperature of the water, the cleaning quality increases marginally as the surface tension reduces.

Note: Here we have to be careful while taking the area. As the ring is hollow, the soap film will be formed on both sides of the ring and we have to consider areas for both sides.