Question

When water ($\eta =0.01$ poise) and benzene ($\eta =0.0065$ poise) are allowed to flow through a capillary tube it was found that the same amount of liquids are collected in the same time. But the pressures that caused the flow are different. If the pressure on water is $0.015atm$. then the pressure on benzene is

• A. $975\times {10}^{-4}atm$
• B. $975\times {10}^{-5}atm$
• C. $975\times {10}^{-6}atm$
• D. $975\times {10}^{-7}atm$

Answer 1

The correct option is B $975\times {10}^{-5}atm$

Now, As the rate of flow of both water and benzene are same we can say from poiseuille's equation,
$\frac{\pi \left(0.015\right)r^4}{\left(0.01\right)8L}=\frac{\pi \left(P_{benzene}{r}^4\right)}{\left(0.0065\right)8L}$
$\Rightarrow P_{benzene}=\frac{0.065\times 0.015}{0.01}atm=9.75\times {10}^{-3}atm$
$=975\times {10}^{-5}atm$