The main difference between a stretched membrane and the liquid surface is

The correct option is: The surface tension does not depend on area but on the tension of the stretched membrane does.

To understand the difference between a liquid surface and a stretched membrane, let us analyze the behavior of both under expansion:

1. Stretched Membrane:
When an elastic membrane (like a rubber sheet) is stretched, its surface area increases, and the molecules within the membrane are pulled further apart. This increases the internal restoring forces, which means the elastic tension in the membrane increases as its area increases. It behaves similarly to a spring, following Hooke's law.

2. Liquid Surface:
A liquid surface also behaves like a stretched membrane because of cohesive forces between molecules, creating surface tension. However, when the surface area of a liquid increases, the distance between the molecules on the surface does not increase. Instead, more molecules move from the bulk (interior) of the liquid to the surface to form the new surface. Since the density of molecules at the surface remains constant, the surface tension (force per unit length) remains constant and does not depend on the surface area.

Therefore, the key distinction is that while the tension in a stretched membrane increases with area, the surface tension of a liquid is independent of its surface area.