Question

The shape of the meniscus for a liquid with angle of contact equal to ${90}^{\circ }$ is:

• A. Flat
• B. Parabolic
• C. Hemispherical
• D. Cylindrical

Answer 1

The correct option is A Flat

For measuring angle of contact $\left(\theta \right)$, a tangent is drawn at the point of contact to the liquid surface and the angle $\theta$ made by the tangent to the liquid surface with the wall of the capillary tube is known as angle of contact.

If the angle $(\theta <{90}^{\circ })$ is acute, the surface of the liquid meniscus is concave. In this case $F_{\text{adhesive}}>F_{\text{cohesive}}$.
Diagram below shows the action of the surface tension in the rise of the liquid column.


If the angle $(\theta >{90}^{\circ })$ is obtuse, the surface of the liquid meniscus is convex. In this case, $F_{\text{cohesive}}>F_{\text{adhesive}}$. This happens in the case of mercury, where the liquid in the capillary tube falls.


If the angle of contact$(\theta ={90}^{\circ })$, the surface of liquid meniscus is flat. In this case, liquid will not rise or fall in the capillary tube.