Question

If $1000$ droplets of water of surface tension $0.07\, N / m$, having same radius $1 \,mm$ each, combine to from a single drop. In the process the released surface energy is- $\left(\right.$ Take $\left.\pi=\frac{22}{7}\right)$

• A. $8.8 \times 10^{-5} J$
• B. $7.92 \times 10^{-4} J$
• C. $7.92 \times 10^{-6} J$
• D. $9.68 \times 10^{-4} J$

Answer 1

Answer: (B)

$ 1000 \times \frac{4 \pi}{3}(1)^3=\frac{4 \pi}{3} R^3 $
$R=10 \,mm$
$ T \times 1000 \times 4 \pi\left(10^{-3}\right)^2- T \times 4 \pi\left(10 \times 10^{-3}\right)^2=\Delta E$
$ \Delta E =4 \times \pi \times 7 \times 10^{-2}[1000-100] \times 10^{-6} $
$\Delta E =7.92 \times 10^{-4} J$