A liquid drop having surface energy ' $E$ ' is spread into 512 droplets of same size. The final surface…

A liquid drop having surface energy ' $E$ ' is spread into 512 droplets of same size. The final surface energy of the droplets is
  1. 2 E
  2. 4 E
  3. 8 E
  4. 12 E

Solution

Surface area of drop, $\mathrm{A}_1=4 \pi \mathrm{R}^2$ Surface area of 512 droplets, $\mathrm{A}_2=512\left(4 \pi \mathrm{r}^2\right)$ volume of drop $=\mathrm{n} \times$ (volume of droplet) $\therefore \quad \frac{4}{3} \pi \mathrm{R}^3=512 \times \frac{4}{3} \pi \mathrm{r}^3$ $\therefore \quad \mathrm{R}=8 \mathrm{r}$ $\therefore \quad \mathrm{A}_2=\frac{512\left(4 \pi \mathrm{R}^2\right)}{64}$ $\therefore \quad \mathrm{A}_2=8\left(4 \pi \mathrm{R}^2\right)$ Surface energy $\propto$ Area $\therefore \quad \frac{E_2}{E_1}=\frac{A_2}{A_1}=\frac{8\left(4 \pi R^2\right)}{4 \pi R^2}$ $\therefore \quad \mathrm{E}_2=8 \mathrm{E}_1=8 \mathrm{E}$ $\ldots .\left(\because E_1=E\right)$

Asked in: MHT CET 2024 (16 May Shift 2)

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