Question

The lower end of a capillary tube touches a liquid whose angle of contact is ${120}^{\circ }$, the liquid

• A. rises into the tube
• B. falls in the tube
• C. may rise or fall inside
• D. neither rises nor falls inside the tube

Answer 1

The correct option is B falls in the tube

We know that,
Capillary rise or fall,
$h=\frac{2T\cos \theta }{\rho gr}$
where $T$ is surface tension and $\rho$ is density of fluid.


Now,
$\cos \theta =\cos {120}^{\circ }$ $[\theta ={120}^{\circ }$, given $]$
$=\cos ({90}^{\circ }+{30}^{\circ })=-\sin {30}^{\circ }=\frac{-1}{2}$

$\Rightarrow h=$ Negative $\Rightarrow$ The liquid falls in the tube.