Two separate air bubble (radii 0.002 m and 0.004 m) formed of the same liquid (surface tension 0.07 N/m) come together to form a double. Find the radius and the sense of curvature of two internal film surface common to both the bubbles.  


Correct option is

0.004 metre


Let the radius of curvature of the common internal film surface of the double bubble formed by two bubbles A and B be r. Excess of pressure as compared to atmosphere inside A is 4T/0.002 and inside B is 4T/0.004. Hence in the double bubble the pressure difference between A and B on either side of the common surface is  


This pressure difference will be 4T/r.


Since pressure inside the smaller bubble is greater than inside the bigger bubble, the curvature of the common film will be concave towards the centre of the smaller bubble. 



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What will be the ratio between the total surface energy of the droplets and the surface energy of the big drop?


 joule work is being done in breaking a big drop of water of radius R into 1000 small drops of equal size. Find out the surface tension of water.


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Two capillary tubes of diameters 5.0 mm and 4.0 mm are held vertically inside water one by one. How much high the water will rise in each tube? (g = 9.8 N kg–1, surface tension of water )