Question

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

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

Answer 1

Answer: (B)

The excess pressure of soap bubble
$p =\frac{4 T}{R}$
$h \rho g =\frac{4 T}{R}$
$\therefore T= \frac{R h \rho g}{4}$
$=\frac{1 \times 10^{-2} \times 2 \times 10^{-3} \times 0.8 \times 10^{3} \times 9.8}{4}$
$= 3.92 \times 10^{-2} N / m$
$=0.0392\, N / m$