What happens to light as it moves from air into water?

• A. It speeds up significantly.
• B. It slows down and bends toward the normal.
• C. It disappears.
• D. It reflects completely off the surface.

Answer: (B)

When light transitions from air into water, it encounters a change in medium, which affects its speed and direction. In air, the speed of light is approximately 299,792 kilometers per second (km/s), while in water, it slows down to about 225,000 km/s. This reduction in speed is due to the higher density of water compared to air.

As light enters water, it also bends towards the normal. The "normal" is an imaginary line perpendicular to the boundary at the point of entry. This bending occurs due to the change in speed as light moves from one medium to another, which is described by Snell's law. This law quantifies the relationship between the angles of incidence and refraction when light crosses the interface between different media.

The other options do not accurately describe the behavior of light in this scenario. Light does not speed up when entering water, nor does it disappear or completely reflect off the surface. Instead, it slows down and bends towards the normal, which is characteristic of refraction, a fundamental property of light behavior at the interface of different media.