How does light behave when entering a less dense medium?

When light transitions from a denser medium to a less dense medium, its speed increases. This change in speed causes the light to bend away from the normal line, which is an imaginary line perpendicular to the boundary between the two media. The bending occurs due to the difference in optical density of the two media, as described by Snell's Law.

As light travels from a material like water (which is denser) into air (which is less dense), it undergoes a refraction that results in this change of direction. The relationship between the angle of incidence and the angle of refraction confirms that as light enters a medium with a lower optical density, it not only speeds up but also bends away from the normal.

This behavior is essential in understanding various optical phenomena, including the formation of rainbows and the designing of lenses, as the bending of light is crucial for focusing and refracting images. The speeding up and bending away from the normal illustrates the fundamental principles of optics concerning light behavior at interfaces of different mediums.