# Calculating the diameter of a bubble

## Homework Statement

Suppose the temperature is 80℃ and we have a soap bubble that has a pressure increase of 40 [Pa]. What is the diameter of the bubble?

ΔP=4Y/R

## The Attempt at a Solution

I'm very confused about how to find the coefficient of surface tension (Y).
In an example my professor gave us in class he gave us Y(20°C)= 0.0728 N/m. So I'm guessing the coefficient changes with temperature? How would I calculate Y(80°C)? Is there a formula I'm missing?

Also I saw a different version of the above formula where they had ΔP=4T/R. Under what condition would you be able to just neglect the coefficient of surface tension and plug the temperature straight in? Or maybe is that formula completely incorrect? Thanks!

Ok! That makes more sense. So how do you find the coefficient of surface tension?

haruspex
Homework Helper
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Ok! That makes more sense. So how do you find the coefficient of surface tension?
Did you try the link I posted?

Does that formula only work for water though? Is there a formula like that for soap?

haruspex
Homework Helper
Gold Member
2020 Award
Does that formula only work for water though? Is there a formula like that for soap?
What if you assume that the difference between water and a soap solution is due to a difference in the critical temperature?

Then you could use that formula?

haruspex