Waves, Sound and Light

1. Waves, Sound and Light Chapters 15 and 16

2. Standards: SPS9. Students will investigate the properties of waves. SPS9a. Recognize that all waves transfer energy. SPS9b. Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves SPS9c. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves. SPS9d. Investigate the phenomena of reflection, refraction, interference, and diffraction. SPS9e.Relate the speed of sound to different mediums. SPS9f. Explain the Doppler Effect in terms of everyday interactions.

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

4. Wave Characteristics • transfer energy • the bigger the wave, the more energy carried • create an erosion force • most are caused by vibrating objects • tsunami: ocean wave caused by earthquakes • wave front: circles spreading out from a wave (each wave front carries same amount of energy)

5. Waves • Two Types: Longitudinal Transverse

6. Anatomy of Waves • crest: high points on transverse wave • trough: low points on transverse wave • compressions: crowded areas on longitudinal wave • rarefactions: stretched-out areas on longitudinal wave

7. Transverse Waves Transverse Waves • medium moves perpendicular to the direction of wave motion ex. electromagnetic waves

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

9. Longitudinal Waves Longitudinal Waves(a.k.a. compressional) • medium moves in the same direction as wave motion ex. sound waves

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

11. 1 second Measuring Waves Frequency( f ) • # of waves passing a point in 1 second • Hertz (Hz) unit • shorter wavelength  higherfrequency  higher energy

12. Measuring Waves Period • time it takes for 1 complete wave cycle

13. Measuring Waves Amplitude: • greatest distance particles in wave move from rest • larger amplitude  greater energy

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

15. v f  Practice: Measuring Waves 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

16. v f  Practice: Measuring Waves 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 = ?

17. V T Measuring Waves: Speed-Period • v = λ T λ – wavelength T -- period λ

18. Measuring Waves: Frequency-Period Frequency-Period • period: time it takes for a wave to pass a certain (T) related to... • frequency: number of wavelengths that pass a given (f) • f = 1 period f 1 T

19. Wave Speed Facts • depends on medium: Fastest- solid>liquid>gas –slowest • speed of light (c) = 3.00 x 108 m/s (finite speed) • visible light is detected by eye • Full light range = electromagnetic spectrum • speed of sound in air = 340m/s

20. Visible Light

21. The Doppler Effect • Doppler Effect: change in frequency of a sound wave when the source or observer is moving • pitch (how high or low): determined by frequencyat which sound strikes eardrum

22. FYI • Doppler radar uses radio wave frequency shifts to track storms since radio waves reflect off of rain, snow and hail

23. Wave Interactions • Reflection: bouncing back of wave when it meets a boundary • Refraction: bending of waves when they pass from one medium to another • Diffraction: bending of waves when they pass around an edge

24. Reflection Refraction Diffraction

25. Interference Combination of two or more waves that combine into a single wave: • Constructive- increases amplitude • Destructive- decreases amplitude (cancels each other out)

26. Light Interference • constructive and destructive waves create different frequencies (colors) ex. rainbow seen in oil on water, iridescent colors on peacock feather

27. Sound Interference • When wave compressions from 2 sources arrive at ear at same time = louder sound (constructive interference) • When wave compression and rarefaction from 2 sources arrive at ear at same time = beat (destructive interference)

28. Standing Waves • Results from interference between wave and its reflection • Causes medium to vibrate in a stationary pattern (loop or series of loops) • Nodes: crest of wave meets its reflected trough (complete destructive interference) • Antinodes: crest of wave lines up with reflected crest; points of maximum vibration; (complete constructive interference)

29. Standing Waves

30. Properties of Sound • longitudinal waves • require medium • spread in air in all directions from source • travel slower in gas; faster in most solids (foam, rubber damper vibrations) • travel faster at hot temperatures (greater collision of molecules)

31. Speed of Sound

32. Pitch • Pitch: wave frequency • ↑ f =↑ pitch • Range of pitch for humans: 20hz – 20,000hz • Infrasound: sound below human hearing • Ultrasound: sound above human hearing

33. Ranges of Hearing for Mammals

34. Loudness • Loudness: determined by intensity (amplitude and distance from sound source) * measured in decibels, dB * threshold of human hearing- 0 dB * threshold of pain- 120 dB

35. Musical Instruments • Produce sound through vibrations of string, air columns, membranes • Rely on standing waves • Use resonanceto amplify sound • Resonance: when two objects naturally vibrate at same frequency (depends on size, shape, mass and materials) (electric guitars don’t resonate well so they require separate amplifiers)

36. Hearing and the Ear Senses vibrations, amplifies them, transmits them to the brain: • Outer ear: Pinna collects sound waves, sends to ear canal, causes tympanumto vibrate • Middle ear: vibrations pass to hammer, anvil, stirrup (small bones act as levers to increase vibrations) • Inner ear: vibrations in cochlea are converted into electrical signals to brain

37. The Ear

38. Ultrasound • High f of ultrasound can travel through most material • Used to measure distance • Reflected waves create image • Sonagram: used in medicine to view internal organs

39. Ultrasound-Sonar • Sound navigation and ranging • Uses reflected sound waves for measurement of distances • Used by marine mammals

40. Sound Project With a partner: Create a musical instrument from scratch that can produce a recognizable tune (ex. Mary Had a Little Lamb, Row, Row, Your Boat, Beethoven’s Fifth Symphony) • Suggested Materials: 5-8 bottles water • Time: 2 class periods

41. The Nature of Light Has dual nature: • Thomas Young’s experiment showed light moves in electromagnetic waves *explains how light waves interfere with each other • Light can also be modeled as a stream of particles * photons: bundles of high energy light units

42. Properties of Light Electromagnetic Radiation • transverse waves produced by motion of electrically charged particles • does not require a medium

43. Speed of Light • depends on medium • ≈ 3.0 x 10⁸ m/s in a vacuum (nothing known is faster) • travels slower outside a vacuum (1.24 x 10⁸ m/s through a diamond)

44. Brightness Intensity: measure of brightness • decreases with distance from light source due to decrease in photons passing through an area

45. Electromagnetic Radiation • made up of electric and magnetic particles • consists of waves of all possible energies, frequencies and wavelenghts • each part of spectrum has unique qualities • used in technologies

46. Types of EM Radiation Radio waves: • longest wavelengths • lowest energy EM radiation • Include TV and radio signals- AM (amplitude modification), FM (frequency modification) • Radar: radio detection and ranging

47. Types of EM Radiation Microwaves: • carry telecommunication signals long distances • penetrate food, vibrate water & fat molecules to produce thermal energy

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

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

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