What is the critical angle in optics?

The critical angle in optics is defined as the angle of incidence at which light traveling from a medium with a higher refractive index to a medium with a lower refractive index is refracted at an angle of 90 degrees to the normal. This phenomenon leads to total internal reflection; thus, if the angle of incidence exceeds this critical angle, all the light is reflected back into the denser medium instead of being refracted into the less dense medium.

Understanding this concept is important in various applications of optics, such as fiber optics, where light needs to be contained within the fiber to transmit information efficiently. The critical angle helps establish the conditions required for total internal reflection to occur, which is crucial for the functionality of these systems.

Other options describe different phenomena that do not accurately capture the definition or implications of the critical angle. For instance, the angle of incidence below which light is absorbed does not define the critical angle, nor does the angle at which light exits a medium correspond to it. The notion of light traveling uninterrupted does not relate specifically to the critical angle, which is fundamentally concerned with the behavior of light at the interface between two different media.