# Waves, Sound and Light Chapters 15 and 16.

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Waves, Sound and Light Chapters 15 and 16

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.

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)

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)

Waves Two Types: Longitudinal Transverse

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

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

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

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

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.

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

Measuring Waves Period time it takes for 1 complete wave cycle

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

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

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

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

Measuring Waves: Speed-Period
T λ – wavelength T -- period V T λ

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

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

Visible Light

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

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

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

Reflection Refraction Diffraction

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

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

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)

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)

Standing Waves

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)

Speed of Sound

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

Ranges of Hearing for Mammals

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

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)

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

The Ear

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

Uses reflected sound waves for measurement of distances Used by marine mammals

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

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

transverse waves produced by motion of electrically charged particles does not require a medium

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)

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

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

carry telecommunication signals long distances penetrate food, vibrate water & fat molecules to produce thermal energy

slightly lower energy than visible light can raise the thermal energy of objects felt as warmth thermogram - image made by detecting IR radiation

slightly higher energy than visible light Types: UVA - tanning, wrinkles UVB - sunburn, cancer UVC - most harmful,sterilization absorbed in ozone layer

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