Question

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

• A. $3.9 N / m$
• 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
$\Rightarrow \frac{4 T}{R}=15.68$
$\Rightarrow \frac{4 \times T}{1 \times 10^{-2}}-15.66$
$\Rightarrow T=3.92 \times 10^{-2} N / m$