Q124 / 160 · AP EAMCET 2010 · Physics
The excess pressure inside a spherical soap bubble of radius $1 \mathrm{~cm}$ is balanced by a column of oil (Specific gravity $=0.8$ ), $2 \mathrm{~mm}$ high , the surface tension of the bubble is
- A$3.92 \mathrm{~N} / \mathrm{m}$
- Correct answerB$0.0392 \mathrm{~N} / \mathrm{m}$
- C$0.392 \mathrm{~N} / \mathrm{m}$
- D$0.00392 \mathrm{~N} / \mathrm{m}$
Solution
The excess pressure of soap bubble
$p=\frac{4 T}{R}$
$h \rho g=\frac{4 T}{R}$
$\therefore T=\frac{R h \rho g}{4}$
$=\frac{1 \times 10^{-2} \times 2 \times 10^{-3} \times 0.8 \times 10^3 \times 9.8}{4}$
$=3.92 \times 10^{-2} \mathrm{~N} / \mathrm{m}$
$=0.0392 \mathrm{~N} / \mathrm{m}$
Hence, the correct answer is option: 'B'.