A certain number of spherical drops of a liquid of radius r coalesce to form a single drop of radius R and…

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:
  1. Energy 4VT1r-1R is released
  2. Energy =3VT1r+1R is released
  3. Energy =3VT1r-1R  is released
  4. Energy is neither released nor absorbed

Solution

U=STA
Ainitial=4πr2n
Afinal=4πR2
A=4πr2n-4πR2
43πr3n=43πR3
n=R3r3
A=4πR3r3.r2-R2=4πR3r-R3R=4πR3331r-1R
A=3V1r-1R
U=3VT1r-1R .

Asked in: NEET 2014

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