Surface tension with the ring method (Du Nouy method)

Principle

The force is measured on a ring shortly before a liquid film tears using a torsion meter. The surface tension is calculated from the diameter of the ring and the tear-off force.

Benefits

• High sensitivity measurement possible thanks to ring method
• Analogue set-up that can also be used as a demo experiment in the lecture hall
• Torsion dynamometer used can measure very small forces and is therefore suitable to measure other electrostatic and magnetic interactions between bodies

Tasks

1. Determine the surface tension of olive oil as a function of temperature.
2. Determine the surface tension of water/methanol mixtures as functions of the mixture ratio.

Learning objectives

• Surface energy
• Interface
• Surface tension
• Adhesion
• Critical point
• Eötvös equation