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Question

The vapour pressure over the concave surface is ______

The correct answer is
Less than the vapour pressure over the plane surface

Vapour Pressure Over Concave Surface

The relationship between vapour pressure and the curvature of a liquid surface is governed by surface tension effects.

Considerations:

  • Surface Tension: Liquid surfaces exhibit surface tension, acting like a stretched membrane. This causes a net inward pull on surface molecules.
  • Concave Surface: In a concave surface, the net effect of surface tension and molecular interactions makes it easier for molecules to escape into the vapour phase compared to a plane surface. Alternatively, the pressure difference across the interface (related to Young-Laplace equation) leads to lower vapour pressure.
  • Result: This increased tendency for evaporation leads to a lower equilibrium vapour pressure over the concave surface.

Therefore, the vapour pressure over the concave surface is less than the vapour pressure over the plane surface.

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Important Questions from Surface Tension

  1. Falling drops of rain break up and coalesce with each other and finally achieve an approximately spherical shape in the steady state. The radius of such a drop scales with the surface tension σ as

  2. The property of a fluid which enables it to resist tensile stress is known as

  3. Above the critical micelle concentration (CMC), the option which correctly describes the variation of molar conductivity with increase in concentration of sodium dodecylsulphate în aqueous solution is

  4. If the surface tension of the soap bubble is 0.035 N/m, then the work done in blowing the soap bubble of radius 5 cm in the air is.

  5. Addition of detergent to liquid

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