Question

The excess pressure inside a small air bubble of radius $0.05mm$ in water of surface tension $70dyne-c{m}^{-1}$ is $Pa$:

• A. $28.2$
• B. $8\times {10}^2$
• C. $5600$
• D. $2800$

Answer 1

Answer: (C)

$5600$

Surface tension is $70dyne/cm$

converting it to $N/m$

we get $\frac{70}{{10}^5}\times {10}^2$ (since ${10}^5$ dyne = 1N)

Excess pressure in bubble = $\frac{4T}{R}$

= $\frac{4\times \frac{70}{{10}^5}\times {10}^2}{0.05\times {10}^{-3}}$

$=5600Pa$

Hence, excess pressure is $5600Pa$