First slide

Surface tension

Question

A certain number of spherical drops of a liquid of radius 'f coalesce to form a single drop of radius 'R' and volume 'V'. If 'T' is the surface tension of the liquid, then :

Moderate

A

$energy = 4 VT (\frac{1}{r} - \frac{1}{R}) is released .$
B

$energy = 3 VT (\frac{1}{r} - \frac{1}{R}) is absorbed$
C

$energy = 3 VT (\frac{1}{r} - \frac{1}{R}) is released$
D

energy is neither released nor absorbed

Solution

As surface area decreases so energy is released
Released energy $= 4 {πR}^{2} T [n^{\frac{1}{3}} - 1]$
Where, $R = n^{\frac{1}{3}} r$
$= 4 {πR}^{3} T [\frac{1}{r} - \frac{1}{R}] = 3 VT [\frac{1}{r} - \frac{1}{R}]$

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