Question

The excess pressure inside a spherical soap bubble of radius $1cm$ is balanced by a column of oil (specific gravity $=0.8),2mm$ high, the surface tension of the bubble is :

• A. $3.92N/m$
• B. $0.0392N/m$
• C. $0.392N/m$
• D. $0.00392N/m$

Answer 1

The correct option is B $0.0392N/m$

The excess pressure of soap bubble
$p=\frac{4T}{R}$
or $h\rho g=\frac{4T}{R}(\because p=h\rho g)$
$\therefore T=\frac{Rh\rho g}{4}$
$=\frac{1\times {10}^{-2}\times 2\times {10}^{-3}\times 0.8\times {10}^3\times 9.8}{4}$
$=0.0392N/m$.