Refraction of Light

1. Refraction of Light

2. What is Refraction? • Refraction is the bending of light as it travels from one medium to another.

3. Refraction • In vacuum, light travels with a speed c = 3.00 x 108 m/s • In a transparent medium, (ex. water or glass) the speed of light is slowerthan its speed in vacuum. • WHY? Ans. interactions between photons and molecules of the medium

4. What does this have to do with refraction? The difference in speed causes light rays to bend (refracted ) when traveling across different transparent materials!!!

5. Refraction Higher speed (lower index of refraction) Normal Refracted ray bends towards the normal θi Air Glass θr Lower speed (higher index of refraction)

6. Refraction Lower speed (higher index of refraction) Normal Refracted ray bends away from the normal θi Glass Air θr Higher speed (lower index of refraction)

7. What is “index of refraction”? • The index of refraction (n) is the ratio of the speed of light (c) in vacuum to that of the speed (v) in the medium. n = c/v

8. Sample Problem What is the speed of light in a diamond if its index of refraction is 2.419? n = 2.419 c = 3.00 x 108 m/s n = c/v = 3.00 x 108 m/s / 2.419 ≈ v = c/n 1.24 x 108 m/s

9. Image NEMO Ok…… so how is knowing about refraction useful? Mmmm..…….Fish and Chips!!! Normal

10. How can we figure out the angle of our refracted ray? • We use Snell’s Law ni(sin θi) = nr(sin θr) Willebrord van Roijen Snell (1580-1626)

11. Sample Problem A light ray traveling through the air strikes a smooth slab of glass at an angle of 30° to the normal. Find the angle of refraction. Normal nr (glass) = 1.52 ni (air) = 1.00 θi = 30° θi Air ni(sin θi) = nr(sin θr) Glass 1.00(sin 30) = 1.52 (sin θr) θr 19.2° θr = sinˉ¹ [(1.00 (sin 30)) / 1.52] =