How are waves generated? Waves are generated by

Transcription

1 WAVES 1

2 How are waves generated? Waves are generated by 2

3 Wave a disturbance that transmits energy through empty space or through a medium Medium any solid, liquid, or gas 3

4 Types of Waves 1. Electromagnetic consists of oscillating electric and magnetic fields a. Requires no medium b. Ex: light, X-rays, radio, gamma rays 4

5 Types of Waves 2. Mechanical energy transferred from one particle of a medium to the next a. Medium required b. Ex: sound, water waves c. 2 types: transverse & longitudinal 5

6 Wave Topics A. Period (p. 516) B. Frequency (p. 516) C. Wave Speed (p ) D. Transverse Waves (p. 511) E. Longitudinal Waves (p. 512) F. The Parts of a Wave (p. 512, ) 6

7 What type of mechanical wave is this? TRANSVERSE

8 Transverse Wave Wave moves perpendicular to the particles of the medium 8

9 Transverse Wave CREST AMPLITUDE WAVELENGTH TROUGH

10

11 What type of mechanical wave is this? Animation 11

12 Longitudinal Wave Wave moves parallel to the particles of the medium 12

13 Longitudinal Wave COMPRESSION RAREFACTION WAVELENGTH

14 Longitudinal Wave

15 Frequency Period # of waves/time time/wave Hertz (Hz) Seconds (s) 1 f T

16 Wave Speed Depends on the medium Wave speed = frequency x wavelength v: velocity (m/s) v f: frequency (Hz) l f l l: wavelength (m) T: period v T

17

18 What are two types of mechanical waves? Longitudinal Transverse 18

19 Review What are the key parts of the following wave? What are the appropriate units for frequency? Frequency is the number of waves that pass a point each second. It is measured in Hertz (Hz). 19

20 Wave Sample Problems Calculate the speed of waves in a puddle that are m apart and made by tapping the water surface 5 times each second. 20

21 Wave Sample Problems Crickets produce a chirping sound based on the outside temperature. Some chirps can have wavelengths in air of 1.25 m. If the speed of sound in air is 346 m/s, what is the frequency of the chirp produced by a cricket? What is its wave period?

22 Wave Sample Problems A manatee can typically hear sounds with frequencies up to 32,000 Hz. What is the speed of sound in water if a wave with this frequency has a wavelength of 10 cm. (Hint: Convert cm to meters.) 22

23 Wave Sample Problems A buoy bobs up and down in the ocean. The waves have a wavelength of 6.3 m, and they pass the buoy at a speed of 12.8 m/s. What is the frequency of the waves? How much time does it take for one wave to pass under the buoy? (Hint: Find the wave period.)

24 Wave Practice Problems, Part 2 check your answers 3) m 4) 10 s 5) m 6) 38 m 7) 1.6 m/s 8) 129 Hz s 9) m/s 10) 1.6 Hz s

25 Review What are the key parts of the following wave? What is the appropriate unit for wave period? 1. Quiz Review 2. Group Review Game Wave period is the amount of time it takes for one wave to pass a given point. It is measured in seconds (s). 25

26 ENERGY A wave is disturbance that transmits ELECTROMAGNETIC waves consists of oscillating electric MEDIUM and magnetic fields and do not require a. ALL FORMS AND COLORS OF LIGHT Examples include. MECHANICAL waves must have a medium because the energy is transferred from through the particles. LONGITUDINAL There are two types of this wave and TRANSVERSE. 26

27 CREST AMPLITUDE WAVELENGTH TROUGH

28

29 The time it takes for one wave to pass a point is called WAVE PERIOD (T) The number of waves that pass in one second is called FREQUENCY (F) These variables are reciprocals (inverse) of each other. T= 1/F or F= 1/T 29

30 AFTER THE QUIZ WAVE BEHAVIORS GUIDED READING

31 Electromagnetic Spectrum

32 The Electromagnetic Spectrum

33 Electromagnetic Waves Vibrating magnetic & electric fields Can travel through a vacuum v = 3.00 x 10 8 m/s (in a vacuum)

34 The Electromagnetic Spectrum

35 Radio Waves Lowest frequency Longest wavelength Radios, TVs, cell phones

36 Microwaves Used in cooking (microwave oven) Food absorbs wave Energy from wave converts to heat

37 Infrared heat waves Uses: keeping food warm, animal tracking, infrared photography

38 Visible Light Different frequencies seen as different colors ROYGBIV Red: lowest frequency, least energy Violet: highest frequency, most energy

39 Ultraviolet Higher frequency than light More penetrable Causes sunburns, damages tissue, kills bacteria

40 X-Rays High energy Can penetrate soft tissue Uses: medical tests, checking luggage at airport

41 Gamma Rays High frequency, short wavelength High energy Produced by nuclear particles Used in radiation treatment to kill cancer cells

42 Draw a transverse wave and label the amplitude. Wave Behaviors Discussion Wave Behaviors lab Lab Explanations

43 Wave Behaviors Reflection Refraction Diffraction Interference

44 Wave Behaviors Reflection Bounces off boundary Refraction The bending of a wave as it moves from one medium to another Diffraction The bending of a wave around a barrier

45 Reflection

46 Refraction

47 Diffraction

48 Interference The combining of 2 waves Two types: Constructive Destructive

49 Constructive Interference

50 Destructive Interference

51 Destructive Interference Waves with different amplitudes

52 Standing Waves Result from interference between a wave and its reflected wave. a1/understandingswdia1.html

53 Node Antinode

54 refraction Destructive interference diffraction reflection

55 Light & Wave Behaviors Lab

56 When light passes through a series of tiny slits or grooves called a diffraction grating, light fans out from each slit. White light is spread out into a spectrum according to wavelength.

57 Refraction Pouring water in the cup causes the light to refract at a different angle. This is why the penny is no longer in view when looking at it from the original viewing angle.

58 Light waves bounce off the inner and outer layers of the nail polish film. At times the waves interfere constructively to produce certain colors and destructively to produce other colors.

59 You could see the image of each other when the angles were the same. The law of reflection states that the angle of incidence equals the angle of reflection.

60 How is amplitude altered during constructive/destructive interference? Constructive interference results a combined wave with a larger amplitude than the separate waves. Destructive interference results in a combined wave with a smaller amplitude than the separate waves. Wave Behaviors Discussion Wave Behaviors lab Lab Explanations

61 Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Constructive Interference Amplitude = 7 cm Sound Notes and Video Clips Resonance Speed of Sound & Sonic Boom Doppler Effect How are frequency and pitch of a sound wave altered as sound moves away from you?

62

63 Sound travels as a longitudinal wave Sound waves are created by vibrations.

64 FREQUENCY Frequency is known as Pitch in sound waves Human hearing: 20 Hz to 20,000 Hz Infrasonic: <20 Hz Ultrasonic: >20,000 Hz

65 AMPLITUDE Amplitude is known as Loudness in sound waves Loudness measured in decibels (db) Near total silence 0 db A whisper - 15 db Normal conversation - 60 db A lawnmower - 90 db A car horn db A rock concert or a jet engine db A gunshot or firecracker db

66 More Sound Terminology Natural Frequency is the frequency at which an object naturally vibrates Resonance occurs when an outside vibration matches the natural frequency of an object causing it to vibrate

67 VELOCITY The speed of a sound wave depends on: 1. The type of Medium Fastest in solids 2. The Temperature of the medium Faster in warmer temps

68 Other Scenarios of Doppler Effect Object is traveling at the speed of sound

69 Other Scenarios of Doppler Effect Object is traveling faster than the speed of sound Creates sonic booms

70 Pitch and the Doppler Effect

71 Wavelength and Frequency Review As the wavelength increases, the frequency. decreases This means wavelength and frequency are indirectly proportional. Which of these waves has the higher frequency? This one! It has the smaller wavelength.

72 Frequency and Sound Frequency = pitch Pitch the highness or lowness of a sound High frequency: high pitch Low frequency: low pitch

73 DOPPLER EFFECT The perceived change in frequency (pitch) due to the motion of either the source of the wave and/or the observer

74 How does it happen? As a sound is created, the sound waves spread out in all directions around the source.

75 If the source moves, the wave becomes bunched up on one side and more spread out on the other. Then What?

76 Doppler Effect If the sound is moving away from you... If the sound is moving towards you... Lower pitch; longer wavelength Lower frequency Higher pitch; shorter wavelength Higher frequency

77 So, what does that mean? If the source is moving towards you, the pitch sounds higher. And if the source is moving away from you, the pitch sounds lower.

78

79 Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Constructive Interference Amplitude = 7 cm How are frequency and pitch of a sound wave altered as sound moves away from you? Frequency will decrease as the sound moves away from you causing the pitch to seem lower. Sound Notes and Video Clips Resonance Speed of Sound & Sonic Boom Doppler Effect

80 REVIEW 1. Review of EM Spectrum 2. Wave Test Review Classify this wave behavior and determine the amplitude if A=2 cm and B=5 cm. Destructive Interference Amplitude = 3 cm Echoes are examples of what wave behavior? Reflections 80

81 The Electromagnetic Spectrum Question & Answer

82 Which EM wave has the longest wavelength, thus the lowest amount of energy? Radio

83 Which EM wave is the only one that can be seen by the human eye? Visible Light

84 Which EM wave is shorter than radio waves, but longer than infrared? Microwaves

85 Which EM wave aids in photosynthesis and provides vitamin D to people? Ultraviolet

86 Which EM wave has the most energy and is the most intense and dangerous? Gamma

87 Which EM wave is used at the airport to see through suitcases and bags? X-rays

88 Which EM wave is the heat given off by objects? Infrared

89

90 Conclusion Electromagnetic Waves: Can travel in a vacuum Speed of all EM waves is 3.0 x 10 8 m/s in a vacuum Slows down in gas, slower in liquids, slowest in solids

91 Review BR: Classify this wave behavior. Refraction How is this different from Diffraction? Refraction is the bending of a wave due as it enters a new medium, but diffraction is the bending of a wave around an obstacle or 91 opening.

92

93

94

95

96 REVIEW Which wave behavior caused this glass to break? Resonance What are the basic properties of sound? 1. Wave Stations 2. QR Code Questions 96

97 Sound Lab Summary Pay close attention as we discuss some of the things you say in the lab activities. You will use this information to explain how each activity worked.

98 Sounds are produced by vibrations. Sound waves are LONGITUDINAL.

99 Frequency = Pitch The shorter the wavelength, the higher the pitch. Humans can hear between 20 Hertz (infrasonic) and 20,000 Hertz (ultrasonic)

100 Natural Frequency All objects produce their own unique frequency and sound (timbre)

101 Resonance When a sound matches the natural frequency of an object causing it to vibrate

102 Amplitude = Loudness Constructive interference creates louder sounds

103 Media Sound travels best (and fastest) through solids Sound cannot travel through empty space

104 1. creates louder sounds. * constructive interference B. destructive interference C. diffraction

105 2. All objects produce their own unique frequency and sound called. A. resonance B. natural pitch * natural frequency

106 3. The longer the wavelength the the pitch? A. longer B. higher * lower

107 4. When a sound matches the natural frequency of an object causing it to vibrate * B. C. resonance natural frequency tone

108 5. Sound travels best (and fastest) through A. gases * solids C. liquids

109 6. Sounds less than 20 Hz are A. supersonic B. ultrasonic * infrasonic

110 REVIEW Which wave behavior caused this glass to break? Resonance What are the basic properties of sound? Sound travels as a longitudinal wave and can experience many different wave behaviors: resonance, constructive/destructive interference, resonance, frequency/amplitude changes. 1. Wave Stations 2. QR Code Questions 110