Question

The potential energy of a molecule on the surface of a liquid compared to the molecules inside the liquid is

• A. zero
• B. less
• C. same
• D. large

Hint:

Physics Tip: This excess potential energy per unit area is exactly what defines surface tension. Liquids naturally try to minimize their surface area to reach the lowest possible energy state.

Answer 1

The Correct Option is D

Concept: Physics (Mechanical Properties of Fluids) - Surface Energy.

Step 1: Analyze the forces on a molecule inside the liquid. A molecule inside the bulk of a liquid is completely surrounded by other molecules. It experiences attractive cohesive forces from all directions, resulting in a net force of zero.

Step 2: Analyze the forces on a surface molecule. A molecule on the surface is not surrounded by as many neighboring molecules. It experiences a net inward pull because there are no liquid molecules above it to balance the downward attractions.

Step 3: Relate work done to potential energy. To bring a molecule from the interior to the surface, work must be done against this inward cohesive pull. This work is stored as additional potential energy in the surface molecules.

Step 4: Conclusion. Consequently, surface molecules possess more potential energy than those in the interior. $$ \therefore \text{The potential energy on the surface is large compared to the inside.} $$