1. 4.2 Travelling waves

2. What is a (travelling) wave?

3. Waves Waves can transfer energy and information without a net motion of the medium through which they travel. They involve vibrations (oscillations) of some sort.

4. Wave fronts Wave fronts highlight the part of a wave that is moving together (in phase). = wavefront Ripples formed by a stone falling in water

5. Rays Rays highlight the direction of energy transfer.

6. Transverse waves The oscillations are perpendicular to the direction of energy transfer. Direction of energy transfer oscillation

7. Transverse waves

10. peak trough

11. Transverse waves Water ripples Light On a rope/slinky Earthquake (s)

12. Longitudinal waves The oscillations are parallel to the direction of energy transfer. Direction of energy transfer oscillation

13. Longitudinal waves compression rarefraction

14. Longitudinal waves Sound Slinky Earthquake (p)

15. Other waves - water

16. A reminder – wave measurements

17. Displacement - x This measures the change that has taken place as a result of a wave passing a particular point. Zero displacement refers to the average position. = displacement

18. Amplitude - A The maximum displacement from the mean position. amplitude

19. Period - T The time taken (in seconds) for one complete oscillation. It is also the time taken for a complete wave to pass a given point. One complete wave

20. Frequency - f The number of oscillations in one second. Measured in Hertz. 50 Hz = 50 vibrations/waves/oscillations in one second.

21. Wavelength - λ The shortest distance between points that are in phase (points moving together or “in step”). wavelength

22. Wave speed - v The speed at which the wave fronts pass a stationary observer. 330 m.s -1

23. Period and frequency Period and frequency are reciprocals of each other f = 1/TT = 1/f

24. The Wave Equation The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ. The speed of the wave therefore is distance/time v = λ/T = fλ You need to be able to derive this!

25. 1)A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving? 2)A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves? 3)The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? 4)Purple light has a wavelength of around 6x10 -7 m and a frequency of 5x10 14 Hz. What is the speed of purple light? Some example wave equation questions 0.2m 0.5m 0.6m/s 3x10 8 m/s

26. Let’s try some questions! 4.2 Wave equation questions

27. Representing waves There are two ways we can represent a wave in a graph;

28. Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm

29. Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD

30. Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD

31. Displacement/time graph This looks at the movement of one point of the wave over a period of time 1 Time s -2 0.10.20.30.4 displacement cm PERIOD IMPORTANT NOTE: This wave could be either transverse or longitudnal

32. Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm

33. Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH

34. Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH

35. Displacement/distance graph This is a “snapshot” of the wave at a particular moment 1 Distance cm -2 0.40.81.21.6 displacement cm WAVELENGTH IMPORTANT NOTE: This wave could also be either transverse or longitudnal

36. Electromagnetic spectrum

37. James Clerk Maxwell

38. Visible light

39. λ ≈ 700 nmλ ≈ 420 nm

40. Ultraviolet waves λ ≈ 700 - 420 nm

41. Ultraviolet waves λ ≈ 700 - 420 nmλ ≈ 10 -7 - 10 -8 m

42. X-rays λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m

43. X-rays λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m

44. Gamma rays λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m

45. Gamma rays λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m

46. Infrared waves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m

47. Infrared waves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m

48. Microwaves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m

49. Microwaves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m λ ≈ 10 -2 - 10 -3 m

50. Radio waves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m λ ≈ 10 -2 - 10 -3 m

51. Radio waves λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m λ ≈ 10 -2 - 10 -3 m λ ≈ 10 -1 - 10 3 m

52. Electromagnetic spectrum λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m λ ≈ 10 -2 - 10 -3 m λ ≈ 10 -1 - 10 3 m

53. What do they all have in common? λ ≈ 700 - 420 nm λ ≈ 10 -7 - 10 -8 m λ ≈ 10 -9 - 10 -11 m λ ≈ 10 -12 - 10 -15 m λ ≈ 10 -4 - 10 -6 m λ ≈ 10 -2 - 10 -3 m λ ≈ 10 -1 - 10 3 m

54. What do they all have in common? They can travel in a vacuum They travel at 3 x 10 8 m.s -1 in a vacuum (the speed of light) They are transverse They are electromagnetic waves (electric and magnetic fields at right angles to each oscillating perpendicularly to the direction of energy transfer)

55. What do you need to know? Order of the waves Approximate wavelength Properties (all have the same speed in a vacuum, transverse, electromagnetic waves) The Electromagnetic Spectrum

56. Sound

57. Sound travels as Longitudinal waves The oscillations are parallel to the direction of energy transfer. Direction of energy transfer oscillation

58. Longitudinal waves compression rarefaction

59. Amplitude = volume

60. Pitch = frequency

61. Range of hearing

62. Humans can hear up to a frequency of around 20 000 Hz (20 kHz)

63. Measuring the speed of sound Can you quietly and sensibly follow Mr Porter?

64. Measuring the speed of sound Distance = 140m Three Times = Average time = Speed = Distance/Average time = m/s

65. 4.2 Measuring the speed of sound Measuring the speed of sound using AudacityMeasuring the speed of sound using Audacity

66. String telephones

67. Sound in solids Speed ≈ 6000 m/s

68. Sound in liquids Speed ≈ 1500 m/s

69. Sound in gases (air) Speed ≈ 330 m/s

70. Sound in a vacuum?

71. echo An echo is simply the reflection of a sound