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Two soap bubbles with radii of curvature R_(1) and R_(2) where R_(2)lt R_(1) are brought into contact as shown in Fig. 21.10. What is the radius of curvature of the film between them? What is the contact angle of the films? |
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Answer» Solution :The pressures from the left and from the RIGHT are equal, i.e. `Delta p_(1)+Deltap=Deltap_(2)= or (4 sigma)/(R_(1))+(4 sigma)/(R)=(4 sigma)/(R_(2))` Here `Delta=4sigma//R`, for the film has two surfaces--the EXTERNAL and the INTERNAL. Hence `(1)/(R)=(1)/(R_(1))-(1)/(R_(2))` Since at the point of contact of the three films we have a system of three forces of equal magnitude in equilibrium in a plane, the angle  between the forces is found from the condition that they form a closed triangle. |
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