What occurs at the critical angle in optics?

At the critical angle in optics, total internal reflection occurs. This phenomenon happens when light attempts to pass from a denser medium to a less dense medium and hits the interface at an angle greater than the critical angle. At this specific angle, all of the light is reflected back into the denser medium instead of being refracted into the less dense medium.

The critical angle is determined by the refractive indices of the two media involved. When the angle of incidence equals this critical angle, the refracted ray travels along the boundary between the two media, and any increase in the angle of incidence will result in no refraction occurring at all, leading to total internal reflection. This principle is essential in various optical applications, such as fiber optics and prisms, where retaining light within the medium is crucial.

Other potential scenarios such as complete absorption, light refracting at a right angle, or entirely transmitting light do not accurately describe what happens at the critical angle. Instead, it is the unique condition of total internal reflection that is observed.