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PRACTICEIntermediate · Single correct

PRACTICE / Excess pressure in drops and bubbles

Count curvature before multiplying

A long cylindrical liquid interface has radius 2.0 mm. A spherical drop of the same liquid has radius 4.0 mm. Each has one liquid–gas interface with the same surface tension. Neglect gravity-induced distortion and cylinder end effects.

What is the spherical pressure jump divided by the cylindrical pressure jump?

Organize the givens & assumptions
  • Cylinder radius = 2.0 mm
  • Sphere radius = 4.0 mm
  • One interface each
  • Same surface tension

Static or initially equilibrated interfaces, constant uniform surface tension, negligible gravity-induced shape distortion where spherical or cylindrical curvature is specified, and negligible evaporation. Capillary heights use the narrow-tube model with equal gas pressures and a large reservoir.

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Problem: Count curvature before multiplying
A long cylindrical liquid interface has radius 2.0 mm. A spherical drop of the same liquid has radius 4.0 mm. Each has one liquid–gas interface with the same surface tension. Neglect gravity-induced distortion and cylinder end effects.
Question: What is the spherical pressure jump divided by the cylindrical pressure jump?
Givens:
- Cylinder radius = 2.0 mm
- Sphere radius = 4.0 mm
- One interface each
- Same surface tension
Assumptions: Static or initially equilibrated interfaces, constant uniform surface tension, negligible gravity-induced shape distortion where spherical or cylindrical curvature is specified, and negligible evaporation. Capillary heights use the narrow-tube model with equal gas pressures and a large reservoir.
Choices (LaTeX):
A. 1
B. 2
C. 1/2
D. 4

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