Question

Due to capillary action, a liquid will rise in a tube if angle of contact is

• A. acute
• B. obtuse
• C. ${90}^0$
• D. zero

Answer 1

The correct option is A acute

According to ascent formula the height/depth $h$ through which a liquid will rise/fall in a capillary tube of 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 $\theta <{90}^o\Rightarrow \cos \theta >0\Rightarrow h>0\Rightarrow$ The liquid will rise when contact angle is acute.
If $\theta >{90}^o\Rightarrow \cos \theta <0\Rightarrow h<0\Rightarrow$ The liquid will fall when contact angle is obtuse.