Question

A glass rod of radius 1mm is inserted symmetrically into a glass capillary tube with inside radius 2mm Then the whole arrangement is brought in contact with the surface of water.Surface tension of water is $7\times {10}^{-2}N/m$.To what height will water rise in the capillary $(\theta =0^o)$

• A. 1.4 cm
• B. 4.2 cm
• C. 2.1cm
• D. 6.8cm

Answer 1

The correct option is A

1.4 cm

let h be the height of the water inside the capillary
$T(2\pi r_1+2\pi r_2)=h(\pi r_2^2-\pi r_1^2)g$
$h=\frac{2T}{(r_2-r_1)\rho g}$
$h=\frac{2\times 7\times {10}^{-2}}{1\times {10}^{-3}\times {10}^3\times 10}=1.4cm$