What is a medium in the context of light?

A medium, in the context of light, is indeed a physical substance that allows energy to travel through it. When light travels, it can pass through various materials, such as air, water, glass, and even solids. The medium is essential because it provides the necessary environment for the propagation of light waves. Different media have different optical properties, which can affect how light behaves as it passes through them, including phenomena like refraction and reflection.

For example, light travels fastest in a vacuum, but when it enters a denser medium like glass, it slows down, which can alter its direction. This interplay between light and different media is crucial for understanding optical concepts such as lenses and prisms. Thus, recognizing a medium as a physical substance that facilitates the transmission of light is fundamental in the study of optics.