What is a ray diagram used for in optics?

A ray diagram is a visual representation that illustrates the path of light rays as they interact with optical devices, such as lenses or mirrors. This tool is essential in optics because it allows for the clear tracking of how light behaves as it travels through different mediums or reflects off surfaces.

In the context of lenses, for example, a ray diagram can show the incoming parallel rays, how they refract upon entering the lens, and converge to a focal point. It helps in identifying important characteristics such as the position of the image formed, its size, and whether it is real or virtual. By analyzing these paths, one can understand the fundamental principles of optics, such as convergence and divergence of light, which are crucial for designing optical instruments and systems.

The other choices—measuring light intensity, demonstrating light absorption, and calculating the speed of light—do not directly pertain to the primary function of ray diagrams, which is specifically to depict the paths and interactions of light as it travels through and reflects off various optical components.