What is a curved surface in a graduated cylinder called?

The curved surface in a graduated cylinder is known as the meniscus. The meniscus is caused by surface tension, which is the cohesive forces between liquid molecules.

In a graduated cylinder containing a liquid, the meniscus may appear concave or convex, depending on the properties of the liquid and the material of the container. A concave meniscus occurs when the liquid molecules have greater attraction to the container walls than to each other, causing the liquid to curve downward at the edges. A convex meniscus occurs when the liquid molecules have greater attraction to each other than to the container walls, causing the liquid to curve upward at the edges.

When measuring the volume of a liquid in a graduated cylinder, it is important to read the measurement at the bottom of the meniscus to ensure an accurate reading. This is especially important when working with transparent or translucent liquids, as the meniscus can distort the measurement if not read correctly.