Question

One end of a glass capillary tube with a radius $r=0.025cm$ is immersed into water to a depth of $h=1cm$. What pressure is required to blow an air bubble out of the lower end of the tube: $T=7\times {10}^{-2}N/m$ and $\rho ={10}^{3}kg/m^3$)

• A. $480N/m^2$
• B. $680N/m^2$
• C. $120N/m^2$
• D. $820N/m^2$

Answer 1

Answer: (B)

$680N/m^2$

$r=0.025cmH=1cm$

$T=7\times {10}^{-2}{Nm}^{-1}\rho ={10}^{3}kg{m}^{-3}$

for a bubble

$P_{min}=\rho gh+\frac{2T}{92}$

$P_{min}={10}^3\times 10\times {10}^{-2}+\left[\frac{2\times 7\times {10}^{-2}}{0.025\times {10}^{-2}}\right]$

$P_{min}=660{NIM}^2$

Answer: $-\left(B\right)680N/M^2$