Question

The excess pressure in soap bubble is 10N / m${}^2$. If eight soap bubbles are combined to form a big soap bubble, then the excess pressure in big bubble is :

• A. 5 N / m${}^2$
• B. 10 N / m${}^2$
• C. 20 N / m${}^2$
• D. 2.5 N / m${}^2$

Answer 1

Answer: (A)

5 N / m${}^2$

If eight soap bubbles are combined, then we have

$\frac{4}{3}\pi R^3=8\left(\frac{4}{3}\pi R_1^3\right)$

$\Rightarrow R=2R_1$

$\therefore P_{ex}=\frac{4T}{R_1}=10N/m^2$

$\therefore \frac{4T}{R}=\frac{4T}{2R_1}=5N/m^2$