fisher ring method is used for
Answers
The du Noüy ring method is a technique for measuring the surface tension of a liquid. The method involves slowly lifting a ring, often made of platinum, from the surface of a liquid. The force, {\displaystyle F} F, required to raise the ring from the liquid's surface is measured and related to the liquid's surface tension, {\displaystyle \gamma } \gamma :
{\displaystyle F=w_{(ring)}+2\pi \cdot (r_{i}+r_{a})\cdot \gamma } {\displaystyle F=w_{(ring)}+2\pi \cdot (r_{i}+r_{a})\cdot \gamma }
where {\displaystyle r_{i}} r_{i} is the radius of the inner ring of the liquid film pulled and {\displaystyle r_{a}} r_{a} is the radius of the outer ring of the liquid film.[1] {\displaystyle w_{(ring)}} {\displaystyle w_{(ring)}} is the weight of the ring minus the buoyant force due to the part of the ring below the liquid surface.[2]
When the ring's thickness is much smaller than its diameter, this equation can be simplified to:
{\displaystyle F=w_{(ring)}+4\pi R\gamma } {\displaystyle F=w_{(ring)}+4\pi R\gamma }
where R is the average of the inner and outer radius of the ring.[2]
This technique was proposed by the French physicist Pierre Lecomte du Noüy (1883–1947) in a paper published in 1925.[3]