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

The correct option is B $3.9\times {10}^{-2}N/m$

The excess pressure inside the bubble is given as,

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

The pressure to height column of oil is given as,

$P=\rho hg$

Since the excess pressure inside the bubble is balanced by the height of the column and it can be written as,

$\frac{4T}{r}=\rho hg$

$T=\frac{0.8\times {10}^3\times 2\times {10}^{-3}\times 9.8\times 1\times {10}^{-2}}{4}$

$T=3.92\times {10}^{-2}N/m$