Question

For a liquid which is rising in a capillary, the angle of contact is:

• A. Obtuse
• B. $180$
• C. Acute
• D. $90$

Answer 1

The correct option is C Acute

The angle $\theta$, which the tangent to the liquid surface at the point of contact makes with the solid surface inside the liquid, is called the angle of contact or the capillary angle.

The angle of contact is acute (less than $90$) in the case of liquids which wet the walls of the container, then liquid rises in the capillary and angle of contact is obtuse (greater than $90$) for the liquids which do not wet the walls of the container, ie, they fall in capillary tube.
Note: The angle of contact for pure water and clean glass is zero for ordinary water and glass, the angle of contact is about $8$, while for mercury and glass the value is $140$.