Refraction of Light

When light travels from an optically less dense medium like air to an optically denser medium like glass, the direction of the light ray is "bent" toward a line perpendicular to the surface of the medium.The perpendicular line is called the normal (₂ < ₁). If the reverse is true; i.e., if the light goes from an optically more dense to a less dense medium, the light is bent away from the normal (₂ > ₁).

This phenomena, called refraction, is due to the fact that light travels at different speeds through different media. For example, light in a vacuum (or air) travels at a speed of three hundred million metres per second (c = 3.00 x 10⁸ m/s), while it travels at that speed in water. The ratio of the speed of light in a vacuum to the speed of light in a medium is called the Index of Refraction.

n = =

Since light travels at its maximum speed in a vacuum, the index of refraction is always a number greater than zero (i.e., the index of refraction of water is n = 4/3).

The amount of bending towards the normal depends on the index of refraction and is given by Snell's Law of Refraction,

=

where the subscripts stand for medium 1 and medium 2.

Go to: https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html

Click on "Intro".

Part 1: Set up the following scenarios, recording the missing information.

Example for the first scenario:

Scenario	Material 1	Index of refraction (n1)	Angle 1	Material 2	Angle 2	Index of Refraction (n2) Calculated	Index of Refraction (n2) Given
1	Air	1	60	Glass	35		1.50
2	Air	1	45	Glass
3	Air	1	60	Water
4	Air	1	45	Water

For each scenario, calculate the expected value of n2 with your data using Snell's Law & compare to the given value of n2.(make sure your calculator is on "degree" mode!)

Example:

Following the same procedure as you did before, experimentally find the index of refraction values for "Mystery A" and "Mystery B".

Scenario	Material 1	Index of refraction (n1)	Angle 1	Material 2	Angle 2	Index of Refraction (n2)
1	Air	1		Mystery A
2	Air	1		Mystery B

Calculations:

Part 2.

Set up a scenario with material on the top to be water and the bottom to be air. Experimentally find the critical angle for which all waves are reflected rather than refracted. Repeat with different materials.

Scenario	Material 1	Index of refraction (n1)	Material 2	Critical Angle
1	Water		Air
2	Glass		Air
3	Mystery A		Air
4	Mystery B		Air

Answer the question: As the index of refraction increases, the critical angle for total internal reflection ______________________.

*Note that this is how fiber optic cables work.The index of refraction is such that the signal is always refracted inwards (inside the cable)