Waves

1. Waves the transfer of energy without the transfer of matter

2. A Simple Look at a Wave • How many wavelengths in the wave below? crest amplitude A wavelength λ trough

3. how many λ pass per second frequency = • units: • per second

4. time for 1 λ to pass by period= or

5. Ex.The wave below takes 10 seconds to pass by. What is the period? What is the frequency?

6. How fast a wave moves Speed

7. Types of Waves Transverse wave: medium vibrates at right angles to the direction the energy moves λ Compression wave: (longitudinal wave) medium vibrates in the same direction as the direction the energy moves

8. Types of Waves

9. Electromagnetic Waves • Mechanical waves require a mediumin order to travel. • examples: • electromagnetic waves do not require a medium water, earthquakes, and sound

10. Electromagnetic Waves All EM waves travel at 3.0 x 108m/s

11. Electromagnetic Waves Radio waves are the longest of the spectrum

12. Electromagnetic Waves Visible light is a tiny section

13. Electromagnetic Waves Visible light is betweenultraviolet (UV) light and Infrared (IR) light v v

14. Interference • Superposition: when two or more waves overlap • Waves do not affect each others identity

15. Interference: Wave Addition

16. Interference • waves add together • overall amplitude is sum of individual wave amplitudes • Interference Example

17. Practice Each wave pulse moves 1 grid at a time

18. Practice Each wave pulse moves 1 grid at a time

19. Practice sketch where wave would be if alone

20. Practice • Waves above rest are positive • below are negative

21. Practice • Add ‘em up +2 0

22. Practice • Add ‘em up +2 +2 0

23. Practice • Add ‘em up 0 +2 -2

24. Practice • Add ‘em up 0 +2 -2

25. Practice • Add ‘em up -2 0 -2

26. Practice • Move another grid and repeat process • (remember, if both same sign then they stack/add) • Now try it yourself

27. SOUND • Sound is a compressionalwave • Speed of sound depends on the medium • fastest in solids (6000 m/s in steel) • slower in liquids (1500 m/s in water) • slowest in gases

28. Speed of sound in Air speed of sound at 0 °C At average temperature: 20 °C If no temperature is given in a problem, assume 20° C (343 m/s)

29. Distance • If you hear lightning 3.0 seconds after seeing it, how far away did it strike?

30. Characterizing Sound • Sounds waves are characterized by their: • speed • pitch • loudness • quality

31. Pitch • Pitch depends on frequency • Young healthy human ear has a range of 20 Hz to 20,000 Hz • Human voice: 120 Hz to 1,100 Hz • Baby cry: 2,000 – 3,000 Hz • Test your range

32. Octaves • The octave is important in music • Octave is the doubling in ƒ • Ear can hear a range of ≈ 10 octaves • 20 Hz  40 Hz  80 Hz  160 Hz  320 Hz  640 Hz  1280 Hz  2560 Hz  5120 Hz  10,240 Hz  20,480 Hz

33. Just Noticeable Difference (JND) • The range that the ear can distinguish tones (pitches) • at <1000 Hz, JND ≈ 1Hz • this means you can tell the difference between 500 Hz and 501 Hz • at 2,000 Hz, JND ≈ 2 Hz • at 4,000 Hz, JND ≈ 10 Hz • Test it

34. Loudness of Sound • depends on amplitude of a sound wave • new unit decibel (db) • decibel is based on human hearing • 0 decibels is the threshold of hearing • 140 db is the sound of a jet on runway

35. Loudness of Sound • decibel scale is logarithmic • So, 60 db  70 db means 10x louder • 60 db  80 db means 100x louder • 140 db is 100,000,000,000,000x louder than 0 db • Test your range

36. Decibel Details • Sound Intensity Level (L) = db • measures how loud you perceive sound • Sound Intensity (I) = W/m2 • measures physical intensity of sound • threshold I = 1 x 10-12 W/m2

37. Decibel Details • threshold = 0 db = 1 x 10-12 W/m2 • I2 = heard sound • I1 = sound you compare to • (usually 1x 10-12 W/m2)

38. Example • How many decibels would sound have if it had an intensity of 1 x 10-10 W/m2? • given: for normal problems, use 1 x 10-12 W/m2 for I1

39. Example • What is the sound Intensity of a girl yelling at 86 db? but this time, we want I2

40. Power! Energy rate produced by a sound units are Watts (W)

41. Power! Power depends only on source, not distance • this can be used to find I at different distances • Start with two instances of the sound (2 P’s)

42. Power Example: What is the power of a jet engine when standing 5.0 m away from it? given: r = 5.0 m L = 140 db need I first

43. Frequency Sensitivity The ear is much more sensitive to some pitches than others. How much more sensitive are we to a crying baby (3,000 Hz) than to normal talking (1,000 Hz)?

44. Practice go to page 129

45. Doppler Effect Pig standing still OINK! λ in front is same as λbehind

46. Doppler Effect Pig running right OINK! λ in front is smaller λthan behind Who hears the higher pitch?

47. Doppler for Everyone!

48. Calculating Doppler Effect • Doppler Effect occurs if either source or listener is moving • ƒ’ = frequency the observer hears • ƒ = actual frequency of source • ν = speed of sound (remember T) • νo = speed of observer • νs = speed of source

49. Picking Signs Ex: On a day when the speed of sound is 350 m/s, a police car with a 2,000 Hz siren and a speed of 35 m/s is chasing a car moving at 50. m/s. What frequency does the driver of the car hear? • what is the source? police car (it has the siren) • what is the observer? chased car Given: moving away from source moving toward the observer

50. Picking Signs Given: So, Now to pick signs. This requires logic.