Question

If the excess pressure inside a bubble of radius 1.0 cm is balanced by a column of oil 3 mm high, find the surface tension of the bubble. Specific gravity of liquid = 0.8.

Answer 1

Given,
Radius, r=1.0 cm
Height, h=3 mm=0.3 cm
Specific gravity of liquid=0.8
$$\begin{gathered} \mathrm{Excess}\mathrm{pressure},\mathrm{P}=\mathrm{h\rho g}=\frac{4\mathrm{T}}{\mathrm{r}} \\ =0.3\times 0.8\times 981=\frac{4\mathrm{T}}{\mathrm{r}} \\ =235.44 \\ \mathrm{or}\frac{4\mathrm{T}}{\mathrm{r}}=235.44 \\ \mathrm{or}\mathrm{surface}\mathrm{tension},\mathrm{T}=\frac{235.44\times \mathrm{r}}{4}=\frac{235.44\times 1}{4}=58.86\mathrm{dyne}/\mathrm{cm} \end{gathered}$$