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

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

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

11. Measuring Waves Frequency ( f ) # of waves passing a point in 1 second
Hertz (Hz) unit
1 second
shorter wavelength  higher frequency  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. 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.
GIVEN:
v = ?
 = 3.2 m
f = 0.60 Hz
WORK:
v =  × f
v = (3.2 m)(0.60 Hz)
v = 1.92 m/s  v f

16. 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?
GIVEN:
 = 417 m
v = 5000 m/s
f = ?
WORK:
f = v ÷ 
f = (5000 m/s) ÷ (417 m)
f = 12 Hz  v f

17. Measuring Waves: Speed-PeriodT
λ – wavelength
T -- period V T λ

18. Measuring Waves: 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 frequency at 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 resonance to 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 tympanum to 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

51. Types of EM Radiation Gamma rays highest energy EM radiation
emitted by radioactive atoms
used to kill cancerous cells (kills healthy cells too)
Radiation treatment using radioactive cobalt-60.

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