Question

The angle of contact at the interface of water-glass is $0^{\circ }$. Ethyl alcohol-glass is $0^{\circ }$. Mercury-glass is ${140}^{\circ }$ and Methyl iodide-glass is ${30}^{\circ }$. A glass capillary is put in trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the trough is:

• A. water
• B. ethylalcohol
• C. mercury
• D. methyliodide

Answer 1

Answer: (C)

mercury

Given ,

Angle of contact $\left(\theta \right)={140}^o$

Radius of tube $\left(r\right)=1mm={10}^{-3}m$

Surface tension $\left(S\right)=0.465N/m$

Density of mercury$\left(\rho \right)=13.6\times {10}^{3}kg/m^3$

Height of liquid rise or fall due to surface tension (h)

$=\frac{2Scos\theta }{r\rho g}$

$=\frac{2\times 0.465\times cos{140}^o}{1\times {10}^{-3}\times 13.6\times {10}^3\times 9.8}$

$=2\times 0.465\times (-0.7660)/{10}^{-3}\times 13.6\times {10}^3\times 9.8$

$=-5.34mm$

Hence, the mercury level will depressed by $5.34$ mm.

The meniscus of liquid in a capillary tube will be convex upward if angle of contact is obtuse. It is so when one end of glass capillary tube is immersed in a though of mercury.