Surface Energy and Surface Tension — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Surface Energy and Surface Tension.

Combined Capillary Action and Temperature Effect

medium

NEET often combines concepts. A question might ask about the change in capillary rise if the temperature of the liquid is increased, requiring knowledge of both Jurin's Law and the effect of temperature on surface tension. For example, 'If water rises to height $h$ at $20^\circ C$, what happens to $h$ if temperature increases to $80^\circ C$?' This tests the understanding that surface tension decreases with temperature, leading to a decrease in capillary rise.

Work Done in Isothermal Expansion of a Soap Film

high

Questions involving work done are a staple. A common variation is calculating the work done to increase the area of a soap film. This directly tests the relationship $W = \gamma \Delta A$, but students must remember the factor of 2 for a film's two surfaces. For instance, 'Calculate the work done to increase the area of a soap film from $A_1$ to $A_2$'. This is a direct application but requires careful attention to the number of surfaces.

Comparison of Excess Pressure in Different Scenarios

high

The distinction between excess pressure in a liquid drop, an air bubble in liquid, and a soap bubble is a frequent point of confusion and thus a common test item. A question might present multiple scenarios and ask to rank or compare the excess pressures, or calculate the ratio. For example, 'What is the ratio of excess pressure in a liquid drop to that in a soap bubble of the same radius and liquid?' This tests the factors of 2 and 4 directly.

Conceptual Question on Wetting and Non-Wetting

medium

While numerical problems are common, conceptual questions about the angle of contact and its implications for wetting are also important. A question might describe a scenario (e.g., water on a lotus leaf vs. on glass) and ask for the relative strengths of adhesive and cohesive forces, or the nature of the meniscus. This requires a qualitative understanding of the angle of contact.