# Homework Help: Two soap bubbles are touching each other.Radius of curvature at point of contact ?

1. Mar 2, 2012

### vkash

Two soap bubbles of radius r and R are in touch find the radius of curvature of their point of contact?
(Both bubbles are touching each other with their external surfaces)

2. Mar 2, 2012

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

What do you know about surface tension?

3. Mar 2, 2012

### vkash

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

No info about surface tension. even answer is in terms r and R.
If you think it can't be done without data related to surface tension then assume that to be S.
answer in book may be wrong...

4. Mar 2, 2012

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

So do you know the answer?

5. Mar 2, 2012

### vkash

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

yeah;
It's answer is given in book. But book doesn't provide procedure.

6. Mar 2, 2012

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

Surface tension does come into it but in this problem it cancels out.Have you studied surface tension?

7. Mar 2, 2012

### vkash

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

yes. (I have read surface tension,angle of contact, capillarity, pressure inside a soap and liquid bubble,change in energy when surface expand or collapse).
How do you approach to this question?

8. Mar 2, 2012

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

Good,so you should know that the pressure inside a bubble is greater than the pressure outside.Now apply that pressure difference formula to the bubbles when they are in contact.There are three radii of relevance r,R and the common radius over their area of contact.

9. Mar 2, 2012

### vkash

Re: Two soap bubbles are touching each other.Radius of curvature at point of contact

Wow!
great;