Question

What should be the radius of a capillary tube if water has to rise to a height of 6 cm in it, if surface tension of water is $7.2\times {10}^{-2}$ Nm${}^{-1}$:

• A. $0.24mm$
• B. $2.4mm$
• C. $2cm$
• D. $1.2cm$

Answer 1

The correct option is A $0.24mm$

Rise height $=\frac{2Tcos\theta }{\rho gr}$

$\frac{6}{100}=\frac{2\times 7.2\times {10}^{-2}}{1000\times r\times 10}$ (taking cos $\theta$ = 1)

$r=\frac{2\times 7.2\times {10}^{-2}}{6\times 10\times 10}$

$r=2.4\times {10}^{-4}$ m

$r=0.24mm$