How does temperature affect the refractive index of a material?

The refractive index of a material is influenced by temperature due to changes in the material's density and its optical properties. As the temperature of a medium increases, its density typically decreases because materials tend to expand upon heating. A decrease in density usually results in a lower refractive index because the speed of light in a less dense medium is higher.

When light travels through a medium, the refractive index is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium. Since the speed of light increases as density decreases due to increased temperature, this leads to the conclusion that the refractive index will decrease.

Therefore, the observation that the refractive index generally decreases with increasing temperature aligns with the underlying physical principles governing light propagation in materials.