Waves – Topic 4

1. Waves – Topic 4 Chapters 26 Reflection & Refraction

2. Reflection • Law of Reflection • The angle of incidence equals the angle of reflection • The incident and reflected rays lie in the same plane with the normal.

3. Image position • You think in straight lines! • The image is located behind the mirror.

4. Diffuse vs Specular Reflection • Diffuse Reflection • Light incident upon a rough surface • Law of reflection still holds; Normals are not parallel. • Specular Reflection • Mirror like reflection • All Normals are parallel

5. Refraction • Sudden change in direction of a wave as it changes speed. • It must enter obliquely to change direction! • Which direction does it bend as it slows?

6. Refraction • In both cases the speed of the wave has decreased. This is indicated by the decrease in wavelength!

7. Refraction • In which medium does light travel faster? (glass rod appears bent)

8. v is the speed of light in the new medium. c= 3.0 x 108m/s As the index increases the speed decrease. Draw a graph for index vs. speed. nis the absolute index of refraction. This is a measure of optical density. n is defined as the ratio of the speed of light in a vacuum to the speed of light in a new medium. Speed of light

9. n is the relative index of refraction. If air is not used, then remember nrel = n2/n1 What is the relative index when going from diamond into lucite? Relative Index of Refraction • If nrel < 1 ; speeds up • If nrel > 1 ; slows down

10. Refraction n(water)=1.33; n(glass)=1.50; n(air)=1.00 Vw = 2.26 x 108m/s Vg = 2.00 x 108m/s Calculate the speed of light in water and glass.

11. When a wave slows down it bends closer to the normal. {less to more – toward} n2>n1 When a wave speed up it bends away from the normal. {BLA – Big ―› Little – Away} n2<n1 Refraction n1- from n2 - into

12. Refraction • If light rays bend closer to the normal when slowing down, why does the glass rod seem to bend away form the normal?

13. Diverging rays enter your eyes. You “think” in Straight Lines. A virtual image appears to come from point y Apparent Depth

14. Apparent Depth • If the chest is 20 m below the surface at what depth will the image appear? Assume nsea water = 1.34

15. Snell’s Law • n1sinθ1 = n2sin θ2 • v1/v2 = λ1 /λ2

16. A monochromatic light ray f= 5.09 x 1014 Hz is incident on medium X at 55˚. The absolute index of refraction for material X is 1.66 Example • What is material X? • Determine the angle of refraction. • Determine the speed of light in medium X.

17. The index of 1.66 is Flint Glass Ex: Solution To find the angle of refraction use Snell’s Law.θ2= 30˚ To find the speed use n=c/v. v = 1.8 x 108 m/s

18. Dispersion • The breaking up of white light into its component frequencies.

19. Refractive & Frequency • The refractive index depends on the medium & the frequency of light. • Each frequency “color” propagates at a different speed and bends a different amount.

20. Critical Angles • Def: The angle of incidence when the angle of refraction is 90 degrees. • Only exist when you have the BLA’s • Big to Little Away • When a light ray exceeds the critical angle it undergoes total internal reflection (TIR)

21. Snell’s Law Lab • What factors effect the index of refraction of a liquid? • Write up a planning A and B for this question. (Last IB Assessment) • Research any procedures you might want to use when investigating. • I may modify your methods based on materials we have available.