Question

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

• A. 10 Pa
• B. 20 Pa
• C. 5 Pa
• D. 2 Pa

Answer 1

The correct option is B

20 Pa

Excess pressure $△P=\frac{4T}{r}$

$=\frac{4\times 2\times 25\times {10}^{-3}}{1\times {10}^{-2}}=20N/m^2$ = 20 Pa (as r = d/2)