The shape of a liquid meniscus, the curved surface of a liquid in a container, is influenced by the angle of contact between the liquid, container, and the surrounding atmosphere. The angle of contact is the angle formed between the tangent to the liquid surface at the point of contact and the surface of the solid container.

There are three main types of menisci based on the angle of contact:

1. Concave Meniscus:

   • Angle of Contact less than 90 degrees: In this case, the liquid wets the solid surface, and the meniscus curves downward. Water is a common example of a liquid that forms a concave meniscus in glass. This is because the cohesive forces between water molecules are stronger than the adhesive forces between water and the solid surface.

2. Convex Meniscus:

   • Angle of Contact greater than 90 degrees: Here, the liquid does not wet the solid surface, and the meniscus curves upward. Mercury is an example of a liquid that forms a convex meniscus in glass. The cohesive forces among mercury atoms dominate over the adhesive forces between mercury and the solid surface.

3. Flat Meniscus:

   • Angle of Contact equal to 90 degrees: In this case, the liquid neither wets nor repels the solid surface. The meniscus appears flat at the point of contact. This is less common and often occurs when the adhesive and cohesive forces are balanced.