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# Topic VI.

## Topic VI.

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##### Presentation Transcript

1. Topic VI. Waves  What is a wave?  How do waves move?  What are the characteristics of waves?  How do waves interact? How do light waves behave?

2. I. Introduction to Waves A. Wave: a disturbance produced by a particle vibrating or oscillating about an average position 1. A wave moves through a medium  body of matter or field 2. Mechanical waves: require a material medium Examples: sound waves & water waves

3. 3. Electromagnetic Waves: produced by changing electric or magnetic field strength at regular intervals  Examples: radio waves, visible light  Can travel through a vacuum

4. 4. Waves transfer ENERGY from the source… NOT mass B.Pulses: a single short disturbance moving through a medium or field

5. 1. When a pulse hits a barrier some of its energy will be…  Reflected: bounced back into medium  Refracted: changes direction/speed  Transmitted: goes through barrier entirely  Absorbed: goes into barrier itself

6. 2. If the barrier is unyielding or more dense, then the pulse will be inverted (Newton’s 3rd Law) 3. If the barrier is “soft” or movable, the reflected pulse will be similar to the original

7. C. Types of Wave Motion 1. Longitudinal: Vibration parallel to direction the source vibrates… a. Longitudinal waves require a material medium b. Examples: sound waves, compression waves, P-waves

8. 2. Transverse: Wave vibration is perpendicular to the direction the source vibrates a. Do not require a material medium b. Examples: electromagnetic waves, S-waves

9. II. Periodic Waves Created when the source of a pulse or wave repeats its vibration at regular time intervals A. Characteristics 1. Frequency: a. Complete = or b. Symbol: f c. Units: # per second ( or s-1) = Hertz (Hz) d. High frequency = High wave energy Number of complete wave cycles per second

10. Time required for one complete wave cycle to pass a point 2. Period: a. Symbol: T b. Units: seconds (s) c. Equation: Note:

11. Example: Frequency and Period • At the beach, you watch the waves come in and a wave crashes every 4 seconds. • What is the period of the wave? • What is the frequency of the wave? • Describe the motion of the water molecules as wave energy travels through.

12. Maximum displacement of a particle from equilibrium position 3. Amplitude: a. Symbol: A b. Units: meters (m)

13. c. Maximum positive displacement is called a crest d. Maximum negative displacement is called a trough

14. e. For Longitudinal waves, maximum amplitude is related to compression of particles  areas of maximum compression are called condensations  areas of minimum compression are called rarefactions

15. f. Amplitude is directly related to:  Intensity for light waves (brightness)  Loudness or Volume for sound waves

16. The distance between identical points in successive wave cycles 4. Wavelength: a. Symbol: λ(Greek letter lambda) b. Units: meters (m) c. The points used to find wavelength are in phase (360° apart)!

17. Example: Wave Diagram

18. Distance that one point on a wave will move per unit time 5. Wave Speed: a. Related to the wave’s frequency and wavelength b. Symbol: v c. Equation: d. Units:

19. Light Speed! (c) = 3.00 x 108 m/s e. Speed of all electromagnetic waves is the same

20. f. Speed of sound waves on Earth at sea level = 3.31 x 102 m/s = 331 m/s = 762 mph *Remember – sound waves are NOT radio waves!  speed of sound depends on air temperature, density, and altitude

21. Breaking the sound barrier…a sonic boom • Constantly Trails the object that is moving

22. Example: Wave Speed, Properties An electromagnetic wave measuring 1 cm from crest to trough travels along and has a frequency of 6.33 x 1014 Hz. Which of the two types of waves is this wave? What is the amplitude of the wave in meters? What is the wave’s speed? Calculate the wavelength of the wave. What kind of electromagnetic wave is this? Compare the speed of this wave to the wave generated by a train whistle…

23. Journal #28 12/13 An electromagnetic wave travels along with a wavelength of 6.12 x 10-7 m. What is the frequency of the wave? (Calculate) What is the period of the wave? Compare the speed of this wave to the speed of sound… and the speed of light. What would the new speed and frequency if the wavelength of the wave changes to 7.5 x 10-7 m?

24. All parts of a wave cycle that are in phase and moving away from the source B. Periodic Wave Phenomena 1. Wave Fronts:  Example: all points on a crest

25. Stretching or compressing of waves due to movement of the source or receiver 2. Doppler Effect: a. Source approaching an observer:  increased frequency  decreased wavelength b. Source moving away from an observer:  decreased frequency  increased wavelength Doppler

26. c. causes changes in pitch in sound waves d. causes changes in color in light waves  Red Shift: source of light moves away from observer (appears more red)  Blue Shift: source of light moves toward observer(appears more blue or violet)

27. e. Doppler Effect is used in meteorology and law enforcement to better obtain speeds of targets (precipitation and speeders)

28. Be QUIET…We will be done faster!!

29. Initial and reflected waves appear to be standing still in a given medium 3. Standing Waves: a. Creates:  Nodes: points that do not move  Antinodes: points of maximum amplitude b. Successive nodes or antinodes appear half a wavelength away from each other ( )

30. Changes to waves occur due to interactions with other waves Occurs when two or more waves travel in the same medium (results in interference) 4. Interference: a. Superposition:  superposition principle: add up displacements from individual waves to get the resultant  Example: Two waves in a medium: Blue = resultant wave  become

31.  Waves combine to form a larger wave b. Constructive Interference: c. Destructive Interference:  Maximum C.I. occurs when waves are “in phase”  Waves combine to form a smaller wave  Maximum D.I. occurs when waves are “out of phase” Interference

32. The natural frequency that a material will vibrate at due to wave exposure 5. Resonance:  the frequency at which a material vibrates is called its natural frequency

33. The spreading out of waves around a barrier 6. Diffraction: a. waves can spread around edges of the barrier b. waves can move through an opening in the barrier – diffracting behind it on both sides

34.  As the size of the opening increases the amount of diffraction __________. decreases

35. Light Diffracts Too!

36. Journal #29 12/16 (b) (a) (c) In the three diagrams below, state the type of interference that will occur between the waves and sketch what the “resultant” wave will look like when the waves pass through each other.

37. III. Light Waves Part of the EM-spectrum that can be seen A. Visible Light: 1. Given off naturally by Stars, Electricity, and Chemical Reactions 2. Travels at the “speed of light” (c)  frequency and wavelength of light can be calculated using the formula: becomes or

38. 3. Each color has a slightly different frequency 4. Light wave particles vibrate up and down as well as left and right  unpolarized 5. Light can be Polarized:  only one direction of vibration is allowed to pass through a material

39. 6. Complimentary Colors  Produce white or black when placed over each other…  Color Wheel

40. B. Light Ray Diagrams 1. Arrows can be drawn perpendicular to wave fronts indicating direction of movement 2. Incident Ray: ray ray Ray that strikes a barrier

41. Line drawn perpendicular to barrier that a ray strikes 3. Normal: 4. Angle of Incidence: Angle to the normal that an incident ray strikes a barrier – Symbol: θi

42. Example: Light Ray Diagram

43. Angle of incidence of a wave equals the angle of reflection C. Law of Reflection: 1. All angles are measured with respect to the normal line! 2. Symbolic Form:

44. 3. Law of Reflection applies to any shape barrier

45. D. Reflection from Mirrors 1. Plane Mirrors a. form virtual images  appear “inside” the mirror  can’t be projected on a screen b. all light rays follow the law of reflection

46. 2. Concave Mirrors a. can form real imagesdepending on how close the object is to the mirror.  appear “outside” the mirror  CAN be projected on a screen  can be magnified or smaller

47. b. images form where reflected light rays intersect!

48. c. objects outside the center of curvature are inverted, real, and smaller