Question

A soap bubble of diameter $8\text{mm}$ is formed in air. If the surface tension of liquid is $30\text{dyne/cm}$, then excess pressure inside the soap bubble is

• A. $150{\text{dyne/cm}}^2$
• B. $300{\text{dyne/cm}}^2$
• C. $3\times {10}^{-3}{\text{dyne/cm}}^2$
• D. $12{\text{dyne/cm}}^2$

Answer 1

The correct option is B $300{\text{dyne/cm}}^2$

We know,
For soap bubble,
$\Delta P=\frac{4T}{r}$
Where,
$\Delta P$ = Excess pressure inside soap bubble.
$T=$ Surface tension of solution/ liquid.
$r=$ Radius of soap bubble.
$\therefore \Delta P=\frac{4\times 30\text{dyne/cm}}{\left(\frac{8\times {10}^{-1}}{2}\right)\text{cm}}=300{\text{dyne/cm}}^2$