Question

The excess pressure inside a soap bubble of diameter $1 \,mm$ is
(surface tension $=60 \times 10^{-3} \,N / m$ )

• A. $240\, N / m ^{2}$
• B. $0.48 \,N / m ^{2}$
• C. $480\,N / m ^{2}$
• D. $0.24 \,N / m ^{2}$

Answer 1

Answer: (C)

Excess pressure $p=\frac{4 T}{r}$
where $T$ is surface tension and $r$ the radius of drop.
Given, $r=\frac{d}{2}=\frac{1}{2} m m=\frac{1}{2} \times 10^{-3} m$,
$T=60 \times 10^{-3}\, N / m$
$\therefore P=\frac{4 \times 60 \times 10^{-3}}{\frac{1}{2} \times 10^{-3}}=480 \,N / m ^{2}$