First slide
Surface tension

A certain number of spherical drops of a liquid of radius r coalesce to form a single drop of radius R and volume V. If T is the surface tension of the liquid, then 


Let n droplets each of radius r coalesce to form a big drop of radius R.

 Volume of  n droplets =   Volume of big drop


n=R3r3          . . . . (i)

 Volume of big drop, V=43πR3      . . . . (ii)

 Initial surface area of n droplets, 

Ai=n×4πr2=R3r3×4πr2(Using . . . (i)) 

=4πR3r=43πR33r=3Vr  (Using . . . . . (ii))

Final surface area of big dropAf=4πR2=43πR33R=3VR  (Using . . . . (iii))

Decrease in surface area 


  Energy released = Surface tension × Decrease in surface area 



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