Final answer:
Refraction is the bending of light waves when light travels between two media with different refractive indexes, changing direction due to the change in speed of light in the different media.
Step-by-step explanation:
The phenomenon of light changing its path when it moves from one transparent medium to another with a different refractive index is known as refraction. Refraction is the bending of light waves, which occurs due to the change in speed of light as it enters a medium with a different density.
The extent to which light bends is determined by the Law of Refraction, also known as Snell's Law. This principle states that when a ray of light passes from a medium with a given refractive index to another with a different refractive index, the ray will bend toward the normal if it is entering a medium with a higher refractive index, and away from the normal if it is entering a medium with a lower refractive index.
For instance, when you observe a straw in a glass of water, the straw appears to be bent at the water's surface. This is due to refraction bending of the light as it moves from the air (lower refractive index) into the water (higher refractive index).
Additionally, when light reflects from a medium having an index of refraction greater or less than that of the medium in which it is traveling, there can be a phase change or shift, which is a separate phenomenon from refraction itself.