Question

Emulsification of $10\, mL$ of oil in water produces $2.4$ x $10^{18}$ droplets. If the surface tension at the oil-water interface is $0.03\, Jm^{-2}$ 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 $= 0.03\, Jm ^{-2}$
Total droplets $= 2.4\times10^{18}$
Area of each droplet $= 125\times10^{-6} \,m^2$
$\Rightarrow $ Total area = Total droplet $\times$ Area of one droplet covered by droplets
$= 2.4\times10^{18} \times12.5\times 10^{-16}$
$= 12.5\times2.4\times 10^2\,m^2$
Energy spent = Total area covered by droplets $\times$ Surface tension
$=12.5\times2.4\times10^{2}\times0.03=90\,J$