When light travels from a rarer (less dense) medium to a denser medium, the angle of incidence changes. According to the laws of refraction, also known as Snell's law, the behavior of light at the interface between two different media can be described.
Snell's law states that the ratio of the sine of the angle of incidence (θ₁) to the sine of the angle of refraction (θ₂) is equal to the ratio of the speeds of light in the two media, which is also equal to the ratio of the indices of refraction (n₁ and n₂) of the two media:
n₁ * sin(θ₁) = n₂ * sin(θ₂)
Here, n₁ and n₂ represent the refractive indices of the initial (rarer) and final (denser) media, respectively.
Based on Snell's law, when light travels from a rarer medium (lower refractive index) to a denser medium (higher refractive index), the angle of incidence (θ₁) is smaller than the angle of refraction (θ₂). This phenomenon is commonly observed and is known as refraction.
In other words, the light ray bends towards the normal (a line perpendicular to the interface) as it enters the denser medium. The greater the difference in refractive indices between the two media, the more significant the change in the angle of incidence.