Understanding Wave Behaviors: Reflection, Refraction & Interference

1. 4.4 Wave Behaviors • Waves interact with media and each other in variety of ways. Changes in speed or obstacles in their path will change their shape and direction. • Reflection • Refraction • Diffraction • Interference

2. Superposition - Interference

3. Superposition

4. Reflection

5. Reflection Law Wave reflection occurs when a wave meets a boundary, and is at least partially diverted backwards. The angles of the rays are always measured with respect to the normal which is perpendicular to the surface. incident = reflect

6. reflective surface reflective surface 4.4 – Wave behavior Reflection and refraction We can also look at the wavefronts: Observe… During reflection what happens to the frequency and the wavelength.=? flat or straight wavefront spherical wavefront

7. Reflected Rays come off hard boundary inverted and reversed in shape.

8. Refraction Refraction occurs when a wave meets a boundary, or a different medium , and is at least partially transmitted. The bending occurs because of a Dv.

9. Refraction of Wavefronts Which side is faster? How can you tell?

10. Ex 1. Wavefronts strike the boundary between clear and muddy water and slow down. Sketch some new wavefronts entering the muddy water. BOUN DARY normal INCIDENT WAVE MUDDY WATER CLEAR WATER

11. BOUN DARY REFRACTED WAVE angle of incidence incidence refraction angle of refraction normal INCIDENT WAVE CLEAR WATER MUDDY WATER

12. Equations of Refraction Frequency is fixed • Index of refraction n = c/v. • sin q1/sinq2 = constant = v1/v2 • n1 sin q1 = n2 sinq2 (Snell’s Law) Do This: • Show that n1/n2 = l1/l2.

13. Snell’s Law • Problem Set

14. Do Now: • A ray of light enters air n=1.00 from water n = 1.33 at an incident angle of 59o. Calculate the angle of refraction. Sketch: • The incident ray, • Reflected ray, • Refracted ray.

15. Critical Angle, qc. • from slow to fast. • It is angle q1 that makes q2. 90o. • For air, n= 1 so: • n1 sin qc= 1 sin 90o . • sin qc= 1/ n1 • . q1 beyond total internal reflection.

16. Ex: The index of refraction of flint glass is 1.47. What is the critical angle for light entering air from flint glass?

17. Ex: The index of refraction of diamond is 2.42. What is the critical angle for light entering diamond from flint glass? Explain.

18. Huygen’s Principle • Brian Lamore start from 1 min • https://www.youtube.com/watch?v=jYQ6EAKt0UU4.3%20JJ%20Wave%20Characteristics.pptx

19. Dispersion

20. Diffraction = bending around boundary.

23. Size of obstacle

24. Displacement vs Time

25. Displacement vs. Distance For a longitudinal:look at the air molecules in their undisturbed positions and compare them as a sound wave passes by. Look at the equilibrium points. See if the particles are displaced left (below) or right (above) or not (0)

26. Hwk Set

28. Light is a small part of the EM spectrum.All EM waves have the same behavior.

30. Light

32. The Visible Spectrum • A range of light waves extending in wavelength from about 400 to 700 namometers.

33. Light & all EM waves are transverse, non-mechanical waves.

34. Electromagnetic Wave Velocity • The speed c is the same for all forms of EM waves in a vacuum of space. • It is ~ 3.0 x 108 m/s. • In air almost the same. • No mass can go the speed of light. • Nothing can go faster.

35. Amplitude is related to the wave energy. So is frequency.High Amplitude means bright.Higher f = higher energy change in color.

36. What is Light/EM waves 2 Models 1) Particles/Photons Packets of energy 2) Electromagnetic Waves energy-carrying waves emitted by vibrating charges. Light displays both types of behavior.

38. A wave entering a new material may change its velocity depending on the properties of the materials.This will result in a bending of the wave either toward or away from a perpendicular to the interface.

39. Law of Refraction - Snell’s Law A ray passing from a faster medium to a slower medium bends toward normal. Qi greater than Qr. What happens to l?

40. For light traveling from a slow medium to a faster one, the refracted ray bends away from the normal. The light coming off fish bends at water/air interface.

41. Refraction of sunlight allows us to see sun a few minutes after it has set below horizon.

42. Amount of “Bending” The amount of bending of light is dependent on the ratio of the 2 speeds. The greater the Dv between the two materials, the greater the bend.

43. “Absoluteindex of refraction, n,” is the ratio of the v light in a vacuum to its v in a medium. n = cn= index of refractionv v = velocity in medium c = speed of light in vacuum - 3 x 108 m/s

44. Ex: The speed of yellow light in calcite is 1.97 x 108 m/s. What is the absolute index of refraction for calcite?

45. n = c v3.00 x 108 m/s = 1.52 (no units)1.97 x 108 m/s

46. Snell’s Law – Law of Refraction • Relates angle of incidence, angle of refraction and the 2 indices of refraction as well as velocity. n1= sin q2= v2. n2 sin q1 v1. n1 = indx refrc med 1. n2 = indx refrc med 2. q1 = angle of incidence q2 = angle of refraction

47. 2. Show that v2 = sinq2. v1 sin q1 • n1sin q1 = n2sin q2 . • c/v1 sin q1= c/v2 sin q2 . • sin q1 = sin q2 . • v1 v2. • v2 = sin q2 v1 sin q1

48. 3. A ray of light enters diamond (n = 2.42) from glycerol (n=1.47) at an incident angle of 40o. Make a scaled sketch showing the: Incident ray Reflected Ray Refracted Ray

49. Read Hamper p92-97 • Do IB question sheet and problems on pg 95.

50. At the boundary the wave is partially:reflected AND partially refracted/transmitted.