What occurs during total internal reflection?

Total internal reflection occurs when light traveling in a denser medium encounters a boundary to a less dense medium at an angle greater than the critical angle. In this scenario, rather than partially refracting into the less dense medium, the light is entirely reflected back into the original, denser medium. This phenomenon requires that the incident light be traveling from a medium with a higher index of refraction to one with a lower index.

The critical angle is a specific angle of incidence above which all of the light is reflected rather than refracted. When the light reaches this boundary, it does not continue into the second medium; instead, it reflects fully, allowing for applications such as fiber optics, where maintaining the light within the core is essential for effective transmission.

The other options all describe processes that do not align with the principles of total internal reflection, such as partial reflection or refraction occurring at more favorable angles, which do not encapsulate the unique characteristic of total internal reflection—complete reflection of light back into the denser medium.