Question

Several spherical drops of a liquid of radius r coalesce to form single drop of radius R. If T is surface tension and V is volume under consideration, then the release of energy is:

• A. $3VT(\frac{1}{r}+\frac{1}{R})$
• B. $3VT(\frac{1}{r}-\frac{1}{R})$
• C. $VT(\frac{1}{r}-\frac{1}{R})$
• D. $VT(\frac{1}{r^2}-\frac{1}{R^2})$

Answer 1

Answer: (B)

$3VT(\frac{1}{r}-\frac{1}{R})$

Since
$W=4\pi r^{2}T\left[n^{(}1/3\right)-1]$
where,
$n=R/r$
So
$W=3\times \left(4\pi r^{3}T/3\right)[1/r-1/R]$
or
$W=3VT[1/r-1/R]$