Waves & Sound

1. Waves & Sound I. Characteristics of Waves • Waves • Transverse waves • Longitudinal waves • Measuring waves

2. A. Waves • Waves • rhythmic disturbances that carry energy through matter or space • Medium • material through which a wave transfers energy • solid, liquid, gas, or combination • electromagnetic waves don’t need a medium (e.g. visible light)

3. B. Waves & Energy • Waves • Carry energy • Waves are caused by vibrations • Can do work • Move objects • Energy • Waves carry energy • Vibration is a transfer of energy • As waves carry energy the particles in the medium move • the direction of the motion determines the type of wave

4. C. Categories of Waves • Mechanical Waves • Must travel through a medium • Cannot travel through a vacuum • Examples: sound, ocean waves • Electromagnetic Waves • Does not require a medium • Can be transferred through a vacuum • Examples: light, UV rays, Visible light

5. D. Types of Waves • Two Types: Longitudinal Transverse

6. D. Transverse Waves • Transverse Waves • medium vibrates perpendicular to the direction of wave motion • Examples: water waves, electromagnetic waves

7. crests wavelength amplitude amplitude nodes wavelength troughs B. Transverse Waves • Wave Anatomy corresponds to the amount of energy carried by the wave

8. E. Longitudinal Waves • Longitudinal Waves (a.k.a. compressional waves) • medium moves in the same direction as the wave’s motion • Examples: sound waves, springs, slinky

9. compression wavelength rarefaction wavelength E. Longitudinal Waves • Wave Anatomy Amount of compression corresponds to amount of energy AMPLITUDE

10. 1 second F. Measuring Waves • Frequency( f ) • # of waves passing a point in 1 second • SI unit: Hertz (Hz) • shorter wavelength  higher frequency  higher energy

11. F. Measuring Waves 1 Frequency = period ( ) or period = the amount of time for one cycle to do a complete motion Cycle second Frequency is measured in hertz (Hz). 1Hz = 1 wave per second

12. F. Measuring Waves • Velocity ( v ) • speed of a wave as it moves forward • depends on wave type and medium v = × f v: velocity (m/s) : wavelength (m) f: frequency (Hz)

13. F. Measuring Waves Solid Liquid Molecules are farther apart but can slide past one another so waves do not travel as fast. • Molecules are close together so waves travel very quickly. Gas • Molecules are very far apart so a molecule has to travel far before it hits another molecule, so waves travel slowest in gases.

14. v f  F. Measuring Waves • EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz. WORK: v =  × f v = (3.2 m)(0.60 Hz) v= 1.92 m/s GIVEN: v = ?  = 3.2 m f = 0.60 Hz

15. v f  F. Measuring Waves • EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency? WORK: f = v ÷  f = (5000 m/s) ÷ (417 m) f= 12 Hz GIVEN:  = 417 m v = 5000 m/s f = ?

16. Waves II. Wave Behavior • Reflection • Refraction • Diffraction • Interference • Constructive Interference • Destructive Interference • Doppler effect

17. A. Wave Interactions • Wave Interaction • When a wave meets an object or another wave. • When a wave passes into another medium • Examples: reflection, diffraction, refraction, interference, resonance

18. Normal incident beam reflected beam A. Reflection • Reflection • when a wave strikes an object and bounces off

19. A. Reflection • When a wave bounces off a surface that is cannot pass through

20. SLOWER FASTER B. Refraction • Refraction • bending of waves when passing from one medium to another • caused by a change in speed • slower (more dense) light bends toward the normal • faster (less dense) light bends away from the normal

21. B. Refraction • The bending of a wave as it enters a new medium at an angle.

22. B. Refraction • Refraction depends on… • speed of light in the medium • wavelength of the light - shorter wavelengths (blue)bend more

23. B. Refraction • Example: View explanation.

24. C. Diffraction • The bending of a wave as it moves around an obstacle or passes through a narrow opening.

25. C. Diffraction • Diffraction • bending of waves around a barrier • longer wavelengths (red) bend more - opposite of refraction

26. D. Interference • The interaction of two or more waves that combine in a region of overlap

27. D. Interference • Two types of Interference • constructive brighter light • destructive dimmer light

28. E/F. Constructive & Destructive Interference • Both are caused by two or more waves interacting, but… • Constructive interference combines the energies of the two waves into a greater amplitude • Destructive interference reduces the energies of the two waves into a smaller amplitude.

29. G. Doppler Effect A change in wave frequency caused by movement of sound source, motion of the listener, or both.

30. Waves & Sound III. The Nature of Sound • Speed of Sound • Human hearing • Doppler effect • Seeing with sound

31. A. Speed of Sound • 344 m/s in air at 20°C • Depends on: • Type of medium • travels better through solids than through liquids • can’t travel through a vacuum • Temperature of medium • travels faster at higher temperatures

32. B. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea

33. B. Human Hearing • Pitch • highness or lowness of a sound • depends on frequency of sound wave • human range: 20 - 20,000 Hz ultrasonic waves subsonic waves

34. B. Human Hearing • Intensity • volume of sound • depends on energy (amplitude) of sound wave • measured in decibels (dB)

35. B. Human Hearing DECIBEL SCALE 120 110 100 80 70 40 18 10 0

36. C. Doppler Effect • Doppler Effect • change in wave frequency caused by a moving wave source • moving toward you - pitch sounds higher • moving away from you - pitch sounds lower

37. lower frequency higher frequency C. Doppler Effect Stationary source Moving source Supersonic source waves combine to produce a shock wave called a sonic boom same frequency in all directions

38. Medical Imaging SONAR “Sound Navigation Ranging” D. Seeing with Sound • Ultrasonic waves - above 20,000 Hz

39. IV. Electromagnetic Radiation • EM Radiation • EM Spectrum • Types of EM Radiation

40. A. Electromagnetic Radiation • Electromagnetic Radiation • transverse waves produced by the motion of electrically charged particles • does not require a medium • speed in a vacuum = 300,000 km/s • electric and magnetic components are perpendicular

41. The full range of light B. Electromagnetic Spectrum

42. B. Electromagnetic (EM) Spectrum long  low f low energy short  high f high energy

43. C. Types of EM Radiation • Rabbits Meet In Very Unusual Xciting Gardens

44. C. Types of EM Radiation • Radio waves • Lowest energy EM radiation • FM - frequency modulation • AM - amplitude modulation • Microwaves • penetrate food and vibrate water & fat molecules to produce thermal energy

45. C. Types of EM Radiation • Infrared Radiation(IR) • slightly lower energy than visible light • can raise the thermal energy of objects • thermogram - image made by detecting IR radiation

46. R O Y G. B I V red orange yellow green blue indigo violet C. Types of EM Radiation • Visible Light • small part of the spectrum we can see • ROY G. BIV - colors in order of increasing energy

47. C. Types of EM Radiation • Ultraviolet Radiation (UV) • slightly higher energy than visible light • Types: • UVA - tanning, wrinkles • UVB - sunburn, cancer • UVC - most harmful, sterilization

48. C. Types of EM Radiation • Ultraviolet Radiation (UV) • Ozone layer depletion = UV exposure!

49. C. Types of EM Radiation • X rays • higher energy than UV • can penetrate soft tissue, but not bones

50. Radiation treatment using radioactive cobalt-60. C. Types of EM Radiation • Gamma rays • highest energy on the EM spectrum • emitted by radioactive atoms • used to kill cancerous cells