Question

if the excess pressure inside a soap bubble is balanced by an oil column of 2mm ,then the surface tension of soap solutition will be (r=1cm ,density of oil= 0.8 g/cm cube )

Answer 1

If the excess pressure inside a soap bubble is balanced by an oil column of $2\mathrm{mm}$, then the surface tension of soap will be? ($r = 1\mathrm{cm}$, density of oil $= 0.8\mathrm{g/cm^3}$)

The excess pressure inside a soap bubble equals:

$$p = \frac {2 \gamma}{r}$$

where $\gamma$ - surface tension of soap, $r$ - radius of the bubble

The pressure of an oil column equals:

$$p = \rho g h$$

where $\rho$ - density of oil, $g$ - acceleration due to gravity, $h$ - high of column

Therefore:

$$\rho g h = \frac {2 \gamma}{r}$$

or:

$$\gamma = \frac {1}{2} \rho g h r = 0.078 \frac {N}{m}$$

Answer: $0.078\frac{N}{m}$