Question

Emulsification of $10mL$ of oil in water produces $2.4$ x $10^{18}$ droplets. If the surface tension at the oil-water interface is $0.03J{m}^{-2}$ and the area of each droplet is $12.5$ x $10^{-16}{m}^2$, the energy spent in the formation of oil droplets is

• A. 90 J
• B. 30 J
• C. 900 J
• D. 10 J

Answer 1

Answer: (A)

Given,
Surface tension $=0.03J{m}^{-2}$
Total droplets $=2.4\times 10^{18}$
Area of each droplet $=125\times 10^{-6}{m}^2$
$\Rightarrow$ Total area = Total droplet $\times$ Area of one droplet covered by droplets
$=2.4\times 10^{18}\times 12.5\times 10^{-16}$
$=12.5\times 2.4\times 10^2{m}^2$
Energy spent = Total area covered by droplets $\times$ Surface tension
$=12.5\times 2.4\times 10^2\times 0.03=90J$