When light enters a prism, which physical property primarily determines the angle at which it is refracted?

The angle at which light is refracted as it enters a prism is primarily determined by the density of the prism material, which is closely related to its refractive index. The refractive index is a measure of how much light slows down when passing through a specific medium compared to the speed of light in a vacuum.

When light transitions from air (a less dense medium) into the prism (a denser medium), it bends towards the normal line, and the extent of this bending is influenced by the material's refractive index, which varies with density. Denser materials generally have higher refractive indices, leading to greater refraction.

Other factors mentioned, such as the color of the light, only influence refraction in terms of wavelength-dependent behaviors (like dispersion), but they do not directly affect the basic angle of refraction determined by the material's density. The temperature of the environment has a negligible effect on refraction in typical conditions, and brightness relates to light intensity rather than the angle of refraction. Hence, the density of the prism material is the key property influencing how light is refracted as it enters the prism.