Question

The surface tension of a soap solution is $25\times {10}^{-3}$ N/m. The excess pressure inside a soap bubble of diameter $1cm$ is:

• A. $5Pa$
• B. $10Pa$
• C. $20Pa$
• D. $40Pa$

Answer 1

Answer: (C)

$20Pa$

The excess pressure is calculated as $\Delta P=\frac{4T}{r}$
$\Delta P=\frac{4\times 25\times {10}^{-3}}{0.5\times {10}^{-2}}=20N/m^2$

$1Pa=1N/m^2$

$\Rightarrow \Delta P=20Pa$

Option C is correct.