Walk students through the lawnmower analogy in Figure 16.17. Demonstrating division using numbers that can be divided easily can reinforce student understanding.Įxplain that, unlike the law of reflection, the law of refraction is most easily expressed as an equation, rather than in words. This, too, is the same change in direction as light going from slow to fast.īe sure students understand that if c is always greater than v, n must always be greater than one. When going from the grass to the footpath, the left front wheel moves faster than the others, and the mower changes direction as shown. This is the same change in direction for light when it goes from a fast medium to a slow one. Going from the footpath to grass, the right front wheel is slowed and pulled to the side as shown. In both cases, you can imagine what happens by thinking about pushing a lawn mower from a footpath onto grass, and vice versa. Conversely, in Figure 16.17(b), the path of the ray moves away from the perpendicular when the ray speeds up. Note that, in Figure 16.17(a), the path of the ray moves closer to the perpendicular when the ray slows down. This difference in index of refraction means that the speed of light is less in medium 2 than in medium 1. In the situations shown in Figure 16.17, medium 2 has a greater index of refraction than medium 1. The change in the speed of light is related to the indices of refraction of the media involved. The change in direction of the light ray depends on how the speed of light changes. As in the previous section, the angles are measured relative to a perpendicular to the surface at the point where the light ray crosses it.
Note, that light travels the slowest in the materials with the greatest indices of refraction.įigure 16.17 provides an analogy for and a description of how a ray of light changes direction when it passes from one medium to another. But during refraction, there is a change in the medium because the light rays enter the second medium on incidence.Table 16.2 Indices of Refraction The table lists the indices of refraction for various materials that are transparent to light. The medium of propagation of light rays does not change during reflection because the light rays only bounce back to form a replica of the image in the medium.But for refraction, since the direction and the medium change, this changes the refractive index and the propagation speed of the light rays. The propagation speed during reflection does not change as there is no change in the medium.Still, the angle of refraction is not equal to the angle of incidence during the phenomenon of refraction because it is seen that the light ray changes direction. The angle of reflection is always equal to the angle of incidence of the light ray on striking the surface. Since the two depend on two different laws, the properties of the angle of reflection and refraction are also different.But for refraction, a transparent surface such as a lens is used. A shining surface, such as a mirror, is used for reflection. Although they are both properties of light rays, they are seen on different surfaces.But during refraction, the light enters the medium, but it experiences a change in the propagation speed and direction. During reflection, the light bounces back into the same medium. Reflection and refraction treat the light rays differently on striking the surface.Main Differences Between Reflection and Refraction
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