Question

If the excess pressure inside a soap bubble is balanced by an oil column of height $2mm$, then the surface tension of soap solution will be $(r=1cm$, density of oil $=0.8g/c{m}^3)$

• A. $3.9N/m$
• B. $3.9\times 10^{-2}N/m$
• C. $3.9\times 10^{-3}N/m$
• D. $3.9\times 10^{-1}N/m$

Answer 1

Answer: (B)

Pressure due to oil column $={\rho }_{\text{oil }}\times g\times h_{\text{oil }}=\frac{0.08\times 10^{-3}}{{\left(10^{-2}\right)}^3}\times 9.8\times 2\times 10^{-3}=15.68$
Now, excess pressure = pressure due to oil column
$\Rightarrow \frac{4T}{R}=15.68$
$\Rightarrow \frac{4\times T}{1\times 10^{-2}}-15.66$
$\Rightarrow T=3.92\times 10^{-2}N/m$