What happens to light when it travels from air to glass?

When light travels from air to glass, it slows down due to the difference in the optical density of the two materials. Air is less optically dense than glass, meaning that light can travel faster in air compared to glass. As light enters a denser medium, such as glass, its speed decreases. This change in speed is accompanied by a change in wavelength, but the frequency of the light remains unchanged.

This phenomenon is governed by Snell's Law, which describes how light refracts, or bends, upon entering a medium with a different refractive index. The slowing down of light in glass is essential in optics, as it is responsible for the bending of light rays, which is a principle used in lenses and other optical devices.

The option that light speeds up is incorrect, as the reduced speed occurs specifically due to the increased density of the glass compared to air. Saying that light remains unchanged overlooks the fundamental change in speed and direction that occurs during this transition. While reflection can occur at the boundary between air and glass, it is not the primary effect considered when discussing the behavior of light entering a new medium.