Question

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

• A. $0^{\circ }$
• B. ${90}^{\circ }$
• C. ${45}^{\circ }$
• D. ${30}^{\circ }$

Answer 1

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

The height of liquid rise in a capillary tube is given by:
$h=\frac{2T\cos \theta }{r\rho g}$
When the level of liquid inside and outside are same, then $h=0$.
Thus, we have
$0=\frac{2T\cos \theta }{r\rho g}$
or $\cos \theta =0^{\circ }$
or $\theta ={90}^{\circ }$