- #1

Quantum Mind

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## Homework Statement

Two soap bubbles of equal radius 'r' coalesce isothermally to form a bigger bubble of radius 'R'. If the atmospheric pressure is P

_{0}, find the surface tension of the soap solution.

## Homework Equations

Surface energy = surface tension x increase in area (W = T.ΔA)

Excess pressure inside bubble = 4T/R i.e. T = p.R/4

## The Attempt at a Solution

Don't know where to start. From the above equation, I thought I can proceed, but I neither know the surface energy nor the surface tension. I also do not know why the term 'p' has been given or how to relate it to the problem.

Probably I should take the area increase as the difference between the total areas of the smaller bubbles and the area of the larger bubble.

Area of smaller bubbles = 2.4∏r

^{2}

Area of bigger bubble = 4∏R

^{2}

Difference in area = 4∏(R

^{2}- 2r

^{2})

W = T.4∏(R

^{2}- 2r

^{2})

= p.R.4∏(R

^{2}- 2r

^{2})/4

How do I proceed further?