Question

The work done in blowing a soap bubble of $10\text{cm}$ radius is -
(surface tension of soap $=0.03\text{N/m}$).

• A. $6.54\times {10}^{-3}\text{J}$
• B. $7.54\times {10}^{-3}\text{J}$
• C. $9.54\times {10}^{-3}\text{J}$
• D. $8.54\times {10}^{-3}\text{J}$

Answer 1

The correct option is B $7.54\times {10}^{-3}\text{J}$

Given,
Radius of soap bubble, $R=10\text{cm}=0.1\text{m}$
Surface Tension, $T=0.03\text{N/m}$
We know, number of free surfaces for soap bubble, $n=2$
Work done $=$ surface tension $\times$ change in surface area $\times$ number of free surfaces
$\Rightarrow W=T\times \Delta A\times n$
$=0.03\times 4\pi ({0.1}^2-0^2)\times 2$
$[$ surface area $=4\pi r^2]$
$=7.54\times {10}^{-3}\text{J}$