1. REFRACTION!!!! The bending of light

3. Aaah! We said before that light travelled in a straight line, so why does this bending of light happen?!?!? It happens because light travels at different speeds in different materials or MEDIUMS Medium: any physical substance through which energy can be transferred.

4. Still…why does this cause light to “bend”? A car will turn towards the slower wheel!!

5. Refraction: the change in direction of light when it travels from one medium to another Angle of Refraction: the angle that a refracted ray makes with the NORMAL!!!

7. Summary If light travels from a faster medium to a slower medium, it will “bend” towards the normal i.e. medium # 1: Fast medium #2: Slow normal incident ray refracted ray ii rr

8. If light travels from a slower medium to a faster medium, it will “bend” away from the normal i.e. medium # 1: Slow medium #2: Fast normal incident ray refracted ray ii rr

9. Phenomenon Resulting from Refraction a) Apparent Depth – objects will appear to be less deep in water than they actually are.

10. Light rays from the object bend away from the normal as they exit the water. The eye then backtracks the refracted ray in a straight line and assumes the light came from that direction (i.e. assumes object is there/sees an image there)

11. b) Bent pencil

12. Similar idea to apparent depth

13. c) Twinkling Stars Different layers of the atmosphere have different temperatures which makes them like different mediums This means light bends as it travels through different layers of the atmosphere Hot air = slower medium Air closer to Earth is warmer (hence slower) This can cause stars to appear in a slightly different position than they actually are

14. Because the air is constantly moving, light from a star won’t take exactly the same path as the light from that same star a second earlier. This makes it look like the stars position is constantly changing This causes the “twinkling” effect of the stars For picture: think of each colour as light from the same star at different times

15. How fast is light??? Light travels fastest in a vacuum. Speed of light in a vacuum is This means it can travel around the Earth 7.5 times in one second!!! (or in other words it takes about 0.13 s to travel around the Earth)

16. Other materials Light travels more slowly in all other mediums The more “optically dense” the material, the slower light travels through it e.g.

17. Index of Refraction A different way to talk about the speed of light in a certain medium It compares the speed of light in that medium to the speed of light in a vacuum. Where c is the speed of light in a vacuum (i.e. ) v is the speed of light in the other medium (in m/s) n is the index of refraction of the other medium (no units associated with this)

18. Example: Calculate the index of refraction of a sapphire if the speed of light in it is 1.70 x 10 8 m/s. n = ? c = 3.00 x 10 8 m/s = 3.00 x 10 8 m/s v = 1.70 x 10 8 m/s 1.70 x 10 8 m/s = 1.76 The index of refraction in sapphire is 1.76.

19. Example: Calculate the speed of light in amethyst if its index of refraction is 1.54. v = ? n = 1.54 c = 3.00 x 10 8 m/s = 3.00 x 10 8 m/s 1.54 = 1.95 x 10 8 m/s Light travels at a speed of 1.95 x 10 8 m/s in amethyst.

20. Which material would have the biggest index of refraction?

21. n for air = 1.00 Diamond : because it is the slowest!

22. Summary Slower mediums = higher index of refraction Faster mediums = low index of refraction – BUT : index of refraction can never go below 1!!! – Why? That would mean it was going faster than in a vacuum!!!

25. Homework Worksheet on index of refraction