4.6 Refraction

Penny Demo

Magic?

Refraction Bending of light as it passes from one medium into another Why? The speed of light is: 3.00 x 108 m/s in a vacuum 2.26 x 108 m/s in water 1.76 x 108 m/s in acrylic

Rules Light bends TOWARDS to normal when the speed decreases Light bends AWAY from normal when the speed increases (up up and away!)

incident ray MEDIUM #1 MEDIUM #2

incident ray MEDIUM #1 MEDIUM #2

incident ray MEDIUM #1 MEDIUM #2

Sample Question If I had a beam of light passing from a water medium to an acrylic medium, would the light bend towards or away from the normal?

Sample Question If I had a beam of light passing from a water medium to an acrylic medium, would the light bend towards or away from the normal?

Angle of Refraction The angle between the refracted ray and the normal (Add this to your diagram)

Partial Reflection and Refraction Some light that hits a surface refracts into the new medium Some of the light is reflected back into the same medium Ex. two way mirrors and mirrored sunglasses

Total Internal Reflection

Critical Angle Angle of incidence increases causing angle of refraction to reach up to 90º. critical angle: the angle of incidence that produces a refracted angle of 90º

Total Internal Reflection total internal reflection: angles greater than the critical angle causing incident ray to be reflected back into same medium DEMO

Summary: Two conditions for total internal reflection: Light must be travelling slower in the first medium compared to the second The angle of incidence must be large enough that no refraction occurs in the second medium

Applications: Diamonds: very high n, therefore very small critical angle, therefore lots of total internal reflection = sparkle Fiber Optics: light travels along glass cable

Triangular prisms: used in optical devices such as cameras and binoculars since they do not deteriorate like the reflective film in mirrors.

Retro reflectors: cut off from corner of cube- used to send light back parallel to incident light. Use on moon, bike reflectors and road signs.