School level

Law of Refraction

Learning goals

  • Illustrate Snell's law of refraction.
  • Explain when total internal reflection occurs.
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Summary

The angle of reflection is equal to the angle of incidence for all wavelengths. The refraction angle depends on the indices n1 and n2 of the two media. This is Snell's law, also known as Descarte’s Law, or The Law of Refraction.

When light passes from one medium to another, some of this light is reflected while another part penetrates into the medium with a change in its direction.

These two phenomena are called the reflection and refraction of light.

  •     The angle of reflection of a ray of light is equal to its angle of incidence.
  •     The angle refraction depends on the refractive indices n1 and n2 of the two media.

Refraction helps explain why a partially immersed object in a liquid seems broken at the surface. This refraction phenomenon also explains why a fish's apparent position is distorted from its real position..

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and drag the fish.
Drag the 'slider' to change the index.

 

Learn more

Consider the example of the fisherman on the shore (index of air n1 = 1) observing a fish in water (n2 > n1). The simulation can show that the fish appears thinner and closer to the surface than it actually is. There is even a maximum angle, called a critical angle (48 °) for which the light is refracted and more light from the fish is totally reflected. This is the phenomenon of total internal reflection. For this critical angle and beyond, it is no longer possible for the angler to see the fish because his image will never reach his eyes!

This battle seems unequal but now let's look at it from the point of view of the fish. A ray of light from the fisherman, located in the air moves from one medium, n1 to another of n2 < n1. The observed object located in the air is further away from the surface than it really is, but also larger. In addition, there is no critical angle for total reflection. In other words, the fisherman will always be visible to the fish, and appear larger, where he sits on the shore!

The phenomenon of refraction is observed with all types of waves: light, sound waves, seismic waves, etc.

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