Question

A capillary tube of radius ${}^{\prime }{r}^{\prime }$ is immersed in a liquid and the liquid level falls in it to height $h$. The contact angle $\theta$ can be

• A. ${85}^{\circ }$
• B. ${70}^{\circ }$
• C. ${95}^{\circ }$
• D. ${80}^{\circ }$

Answer 1

The correct option is C ${95}^{\circ }$

It liquid level falls in capillary tube,
$\therefore h<0$
$\Rightarrow \frac{2T\cos \theta }{r\rho g}<0$
$\Rightarrow \cos \theta <0$
$\Rightarrow \theta >{90}^{\circ }$
$\therefore {95}^{\circ }$ can be the contact angle.
Option (c) is correct.