Constant Temperature Bubble Expansion: Work Calculation for Changing Radius

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SUMMARY

The discussion focuses on calculating the work required to expand a soap bubble from radius R_1 to R_2 at constant temperature, utilizing the formula ΔW = P_2V_2ln(P_2/P_1) along with considerations for surface tension and atmospheric pressure. The integral ∫(V_1+v)^(V_2) PdV is highlighted as a critical component for determining the work done, with the ideal gas law being referenced for pressure-volume relationships. Participants emphasize the importance of correctly applying logarithmic identities to simplify calculations, specifically ln(P2/P1) = -ln(V2/V1).

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Grand
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Homework Statement


A soap bubble of radius R_1 and surface tension \gamma is expanded at constant temperature by forcing in air by driving in fully a piston containing volume v. We have to show that the work needed to increase the bubble's radius to R_2 is:

\Delta W=P_2V_2ln\frac{P_2}{P_1} + ...

I know hoow to work out the dots (due to surface tension and work against the atmosphere. But for the first term I need to work out the integral:

\int_{V_1+v}^{V_2} PdV
which I don't really know how to do. If I apply the ideal gas law, I pick a minus sign on the way.
 
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Hi Grand! :smile:

(write "itex" rather than "tex", and it won't keep starting a new line :wink:)

ln(P2/P1) = - ln(V2/V1) … does that help?

if not, show us what you got :smile:
 

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