Evans SPH 3U1

Unit 3: Light and Optics

Note 4: Refraction, Snell's Law

Reference: Chapter 11.1, 11.2, 11.3

Demos:

Vanishing Beaker: Place small beaker in large beaker. Pour oil into the small one, allowing the oil to overflow. The small beaker will disappear. (i.e. oil and Pyrex glass have the same index of refraction)

Magic Trick: Before class, immerse a test tube upside down in a beaker filled with oil (or glycerin). In class place a test tube in a bag and break it into pieces. Pour the pieces into the beaker. Now pull out the full hidden test tube with tongs.

Fibre Optics in Water: Punch a hole near the bottom of a 2L plastic bottle. Fill the bottle with water (plug hole with finger temporarily). Shine laser so the passes through the bottle and out the hole on the other side. Unplug the hole. Shows total internal reflection)

Refraction:

Refraction is the bending of light as it passes from one medium into a different medium.

where n is the index of refraction of the medium, c is speed of light in a vacuum, v is the speed of light in the medium

Example 1: Given that the index of refraction of quartz is 1.46, calculate the speed of light in quartz.

Page 360 # 1ab, 2ab

Snell's Law:

where is the index of refraction of 1st medium and is the angle of incidence for the 1st medium.

Example 2: Find the angle of refraction for light travelling from air to flint glass if the angle of incidence in air is 20 degrees. Note index of refraction of air is 1.00 and for flint glass it is 1.91.

Example 3: Calculate the index of refraction for a substance where the angle of incidence is 30.0 degrees, the angle of refraction is 45 degrees and the index of refraction of the second medium is 1.50.

When travelling from a less dense optical medium to a more optically dense medium, light bends towards the normal.

When travelling from a more dense optical medium to a less optically dense medium, light bends away from the normal