Question

The pressure of air inside a soap bubble of diameter $0.7cm$ is $8mm$ of water above atmospheric pressure, the surface tension of soap solution is :

• A. $9.8\times {10}^{-1}N/m$
• B. $6.86\times {10}^{-2}N/m$
• C. $7.2\times {10}^{-2}N/m$
• D. $1.37\times {10}^{-1}N/m$

Answer 1

Answer: (B)

$6.86\times {10}^{-2}N/m$

Excess pressure inside a soap bubble is given by-

$\Delta P=\frac{4T}{r}$

$⟹\rho gh=\frac{4T}{r}$

$⟹{10}^3\times 9.8\times 0.008=\frac{4T}{0.0035}$

$⟹T=6.86\times {10}^{-2}N/m$