Refraction is caused by the change in speed experienced by a wave when it changes medium. In Lesson 1, we learned that if a light wave passes from a medium in which it travels slow (relatively speaking) into a medium in which it travels fast, then the light wave would refract away from the normal.
Q. Why does light take shortest path?
Light does travel on the path which would take the shortest time to travel between two points. This nature of light best explains the refraction of light when traveling across two mediums of different refractive index. Light does travel on the path which would take the shortest time to travel between two points.
Table of Contents
- Q. Why does light take shortest path?
- Q. Why does light travel slower in a medium?
- Q. What if the waves are traveling at right angles to the boundary is there a change in the direction?
- Q. Do frequency and wavelength change when light passes from one medium to another?
- Q. Why does a light ray slow down and bend toward the normal when it passes from a less dense medium to a denser medium?
- Q. What happens when light passes from rarer to denser medium?
Q. Why does light travel slower in a medium?
Light moves slower through denser media because more particles get in its way. Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
Q. What if the waves are traveling at right angles to the boundary is there a change in the direction?
The only time light waves do not bend when changing speed, is if they are travelling along the normal line, at right angles to the boundary. If the ray doesn’t hit the block at right angles one side will hit before the other. This slows one side of the ray down first, which makes the ray change direction.
Q. Do frequency and wavelength change when light passes from one medium to another?
When waves travel from one medium to another the frequency never changes. As waves travel into the denser medium, they slow down and wavelength decreases. Part of the wave travels faster for longer causing the wave to turn.
Q. Why does a light ray slow down and bend toward the normal when it passes from a less dense medium to a denser medium?
The normal is a line perpendicular (forming a 90 degree angle) to the boundary between the two substances. The bending occurs because light travels more slowly in a denser medium. Since the light is passing from air (less dense) into water (more dense), it is bent towards the normal.
Q. What happens when light passes from rarer to denser medium?
You saw that light bends toward the normal in this situation, and that the angle in the denser medium will be smaller than the angle in the rarer medium. When light travels from a denser medium to a rarer medium, it bends away from the normal, as illustrated to the left. This behavior follows from Snell’s Law.
