Question

If a capillary tube is dipped and the liquid levels inside and outside the tube are same, then the angle of contact is:

• A. Zero
• B. ${90}^0$
• C. ${45}^0$
• D. Cannot be obtained

Answer 1

The correct option is B ${90}^0$

The height $h$ through which a liquid will rise in a capillary tube of inner radius $r$ is given by
$h=\frac{2S\cos \theta }{r\rho g}$
Where $S$ is the surface tension, $\rho$ is the density of the liquid and $\theta$ is the angle of contact.
If the liquid level inside and outside of the tube are same. We have $\cos \theta =0$, Since other variables can't be zero.
$\cos \theta =0$
$\Rightarrow \theta ={90}^{\circ }$
So the correct option is 'B'.