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. ${90}^{\circ }$
• C. ${45}^{\circ }$
• D. ${60}^{\circ }$

Answer 1

The correct option is B ${90}^{\circ }$

We know that, capillary rise or fall $\left(h\right)$
$h=\frac{2T\cos \theta }{\rho gr}$


$T\to$ surface tension
$\rho \to$ density of fluid
As, liquid levels inside and outside the tube are same.
$\Rightarrow h=0$
$\Rightarrow \frac{2T\cos \theta }{\rho gr}=0$
$\Rightarrow \cos \theta =0$
$\Rightarrow \theta ={90}^{\circ }$
The angle of contact of the liquid with tube is ${90}^{\circ }$.