Refraction & Reflection (Iris Dorn)

Quickwrite

Title: Refraction of Light through Different Mediums

Principle(s) Investigated: Light, Reflection, Index of Refraction, Refraction, Speed of Light.

Standards :

Next Gen Science Standard:

The most effective way to find the indices of refraction for materials is to compare and calculate with Snell's Law:

In this diagram, the light is travelling from Medium 1 to Medium 2 through the Incident Ray with angle Theta (1).

Theta (1) is called the Angle of Incident.

When the Incident Ray meets the interface of Medium 1 and 2, some light is reflected in the direction of the Reflected Ray with the same angle, Theta(1), opposite to the normal of the interface.

The rest of the light travels through Medium 2 in the direction of the Refracted Ray with an angle of Theta (2).

Theta (2) is called the Angle of Refraction.

If you know the index of refraction (n) of one medium, such as n= 4/3 for water, then you can calculate the index of refraction for the other medium. Here is a list of index of refraction for different mediums.

Below, we see the incident ray travelling through glass and into the medium of air, where the speed is faster bends away from the normal (shown here by a dashed red line). If there were no change in speed in the new medium, the path would have been ray C. If the speed had slowed in the new medium, the path would be ray D. But the speed is faster in air than in glass, so the path is ray B. This is because the index of refraction for glass is approximately n=1.5 and the index of refraction for air is n=1.000277. If the indices were the same, it would travel straight through ray c.

So, now we can explain why the Pyrex stirring rod seems to disappear in the beaker of Wesson Oil.

Their indices are nearly the same! They both are around n = 1.474.

Instead of reflecting some light, nearly all of the light passes through the Pyrex at the same speed with nearly no

reflection and nearly no refraction.

Videos:

Questions & Answers:

• Question: We want to know the index of refraction for a new material called Glassairium. How could we do this out?
• Answer: We would use Snell's Law. We know the index of refraction of other materials such as air. We could force light to travel (also know as a laser) at a known angle (we measure this from the normal of the interface) and then measure the angle of refraction through the medium of Glassairium. Using algebra, we can now find the index of refraction of Glassairium.
• Question: Could we market devices that calculate the location of refracted images?
• Answer: Most likely. Many fisherman would love to know how to spear a fish precisely.
• Question: Where could I learn more about light acting like particles and waves?
• Answer: Read Richard Feynman's book QED. My most favorite book of all time.

Applications to Everyday Life:

• The military has heavily interested in camouflage. See the video below for details of a disappearing tank.

• When spearfishing, hunters must be aware of the affects of refraction from light travelling from air to water and throw their spears accordingly.

• The eye's cornea and inner lens is responsible for the formation of images. There is a different in refraction indices between the medium the light travels through and the cornea and inner lens of the eye, This allows images to be projected and focused on the back of the eye.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Source: Disappearing glass rods: Reflection, refraction & light science activity exploratorium science snacks. (n.d.). Retrieved from http://www.exploratorium.edu/snacks/disappearing_glass_rods/