When light is incident at angles less than the critical angle, what happens?

When light is incident at angles less than the critical angle, it refracts into the next medium. This phenomenon occurs due to the bending of light as it passes from one medium into another where the optical densities differ, such as from air into water. The angle of incidence is less than the critical angle, allowing light to enter the second medium rather than reflecting back entirely.

The critical angle is defined as the minimum angle of incidence at which light can be totally internally reflected. When the angle of incidence is below this critical angle, some of the light will refract into the second medium (for example, from air into water), which means that the light passes through the interface between the two media and continues its path in the new medium, bending at the interface according to Snell's law.

This behavior is crucial for understanding concepts related to lenses, optical fibers, and other applications of optics where the interaction of light with different materials is significant. In circumstances where the angle of incidence exceeds the critical angle, total internal reflection occurs instead.