What happens to the refractive index of gases as temperature increases?

As temperature increases, the refractive index of gases typically decreases. This phenomenon occurs because as gases are heated, the density of the gas lowers. The refractive index is influenced by density—specifically, a lower density leads to lower refractive indices. Since the refractive index is a measure of how much light bends as it passes through a medium, a decrease in density means that light will be less impeded and can travel through the medium more freely.

In gaseous media, this relationship allows us to see that as temperature rises and the gas expands (increasing the volume while decreasing the density), the ability of the gas to influence the speed of light diminishes, resulting in a lower refractive index.