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Waves, Sound and Light
Chapters 15 and 16
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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 ofelectromagnetic 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 everydayinteractions.
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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)
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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)
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Waves
• Two Types:
Longitudinal Transverse
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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
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Transverse Waves
Transverse Waves• medium moves
perpendicular to the direction of wave motion
ex. electromagnetic waves
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Transverse Waves
• Wave Anatomy
crests
troughswavelength
wavelength
amplitude
amplitude
corresponds to the amount of energy carried by the wave
nodes
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Longitudinal Waves
Longitudinal Waves (a.k.a. compressional)• medium moves in the same direction as wave motion ex. sound waves
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Longitudinal Waves
• Wave Anatomy
rarefaction
compression
wavelength
wavelength
Amount of compression corresponds to amount of energy AMPLITUDE.
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Measuring Waves
Frequency ( f )• # of waves passing a
point in 1 second• Hertz (Hz) unit
shorter wavelength higher frequency higher energy
1 second
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Measuring Waves
Period• time it takes for 1 complete wave cycle
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Measuring Waves
Amplitude:• greatest distance particles in wave move from
rest• larger amplitude greater energy
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Measuring Waves- SpeedVelocity ( 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)
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WORK:v = × f
v = (3.2 m)(0.60 Hz)
v = 1.92 m/s
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 mf = 0.60 Hz
v
f
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WORK: f = v ÷
f = (5000 m/s) ÷ (417 m)
f = 12 Hz
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 = ?
v
f
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Measuring Waves: Speed-Period
• v = λ T λ – wavelength T -- period V T
λ
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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
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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
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Visible Light
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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
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FYI
• Doppler radar uses radio wave frequency shifts to track storms since radio waves reflect off of rain, snow and hail
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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
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RefractionReflection Diffraction
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InterferenceCombination of two or more waves thatcombine into a single wave:• Constructive- increases amplitude
• Destructive- decreases amplitude (cancels each other out)
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Light Interference
• constructive and destructive waves create different frequencies (colors)
ex. rainbow seen in oil on water, iridescent colors on peacock feather
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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)
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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)
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Standing Waves
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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)
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Speed of Sound
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Pitch
• Pitch: wave frequency • ↑ f = ↑ pitch • Range of pitch for humans: 20hz – 20,000hz• Infrasound: sound below human hearing• Ultrasound: sound above human hearing
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Ranges of Hearing for Mammals
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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
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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)
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Hearing and the Ear
Senses vibrations, amplifies them, transmitsthem 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
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The Ear
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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
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Ultrasound-Sonar
• Sound navigation and ranging
• Uses reflected sound waves for measurement of distances
• Used by marine mammals
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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
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The Nature of Light
Has dual nature:1. Thomas Young’s experiment showed light moves in
electromagnetic waves *explains how light waves interfere with each other2. Light can also be modeled as a stream of particles * photons: bundles of high energy light units
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Properties of Light
Electromagnetic Radiation• transverse waves produced by motion of
electrically charged particles• does not require a medium
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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)
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Brightness
Intensity: measure ofbrightness• decreases with distance
from light source due to decrease in photons passing through an area
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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
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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
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Types of EM Radiation
Microwaves:• carry telecommunication signals long
distances• penetrate food, vibrate water & fat molecules
to produce thermal energy
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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
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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
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Types of EM Radiation
X rays• higher energy than UV• can penetrate soft tissue,
but not bones
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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.
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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