Question

A capillary tube of radius 0.50 mm is dipped vertically in a pot of water. The difference between the pressure of the water in the tube 5.0 cm below the surface and atmospheric pressure is …….
[Surface tension of water = 0.075 N/m]

• A. $100N/m^2$
• B. $190N/m^2$
• C. $380N/m^2$
• D. $80N/m^2$

Answer 1

The correct option is B $190N/m^2$

$P_A=P_a$
$P_B=P_a-\frac{2T}{r}$ and
$P_C=P_B+h\rho g$
= $(P_a-\frac{2T}{r})+h\rho g$
$\therefore P_C-P_a=h\rho g-\frac{2T}{r}$
$=0.05\times {10}^3\times 9.8-\frac{2\times 0.075}{0.5\times {10}^{-3}}$
$=190N/m^2$