4 6 Refraction Penny Demo Magic Refraction Bending

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 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.