Two soap bubbles coalesce. It is noticed that whilst jointed together, the radii of the two bubbles are a and b where a >b. Then the radius of curvature of interface between two bubbles will be

Lot the radius of curvature of the common internal film surface of the double bubble formed by two bubbles be r. excess of pressure as compared to atmosphere inside A is (4T / α). h double bubble, the pressure difference between A and I on either side of the common surface=4Tb−4Ta  This will be equal to (4T/r) ∴ 4Tr=4Tb−4Ta or 1r=1b−1a=a−bba or r=aba−b