Question

The pressure inside a soap bubble of radius $1cm$ balances $1mm$ of a column of oil of specific gravity $0.8$. lf the surface tension of the soap solution (in $N/m$) is $T=n\times {10}^{-2}$, find $n$. (Take acceleration due to gravity to be $10m/s^2$)

Answer 1

Pressure difference between inside and outside of the soap bubble is:
$\Delta P=P_2-P_1=\frac{4T}{r}=h\rho g$
$\therefore T=\frac{h\rho gr}{4}$
$\therefore T=\frac{1\times {10}^{-3}\times 0.8\times {10}^3\times 1\times {10}^{-2}\times 10}{4}=2\times {10}^{-2}$
$\therefore n=2$