What is total internal reflection?

Total internal reflection is a specific optical phenomenon that occurs when light attempts to pass from a denser medium to a less dense medium, such as from water to air. For total internal reflection to occur, the light must strike the boundary at an angle greater than a certain critical angle specific to the two media involved.

When this condition is met, rather than refracting into the second medium, all of the light is reflected back into the denser medium. This is what gives rise to the term "total" internal reflection, indicating that there is no transmission of light into the less dense medium—it is entirely reflected. This principle is a key concept in various applications, such as fiber optics, where light is guided through a medium using repeated total internal reflections, ensuring minimal loss of light and maintaining the signal strength.

In the context of the other choices, while they touch on related concepts, they do not accurately define total internal reflection as it requires that specific condition of the angle of incidence exceeding the critical angle for complete reflection to occur.