Due to surface tension, the excess pressure inside a smaller drop is 9 units. If 27 smaller drops combine,…
Due to surface tension, the excess pressure inside a smaller drop is 9 units. If 27 smaller drops combine, then the excess pressure inside the bigger drop is
$2$ units
$1$ unit
$3$ units
$4$ units
Solution
Given $P_{\text {in }}-P_{\text {out }}=\frac{4 T}{r}=9$ units If 27 such drop coalesee $27\left(\frac{4}{3} \pi r^{3}\right)=\frac{4}{3} \pi r_{b}^{3}$
$\therefore \quad 3 r=r_{b}$
$\therefore$ Excess pressure $\frac{4 \mathrm{~T}}{\mathrm{r}_{\mathrm{b}}}=\frac{4 \mathrm{~T}}{3 \mathrm{r}}=\frac{9}{3}=3$ unit