Waves
Sound Waves and Electromagnetic Waves
Georgia Performance Standards
SPS9. Students will investigate the properties of waves.
a. Recognize that all waves transfer energy.
b. Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves.
c. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves.
d. Investigate the phenomena of reflection, refraction, interference, and diffraction.
e. Relate the speed of sound to different mediums.
f. Explain the Doppler Effect in terms of everyday interactions.
What is a wave?
• A rhythmic disturbance that transfers energy through matter or space.
• The wave exists only as long as it has energy to carry
When a wave hits a boat, does it carry the boat along? Explain. NO, the matter (water) moves up and down, the wave moves horizontally.
What is the source of a wave?
• Vibrations cause waves.
• Vibrations are REPEATING DISTURBANCES.
• When an object vibrates, it is moving, therefore it has energy which is given off to a nearby particle causing them to vibrate as well.
Mechanical Waves• Some waves must have substance to travel
through and some do not.
Mechanical Waves must have a material to travel through (vibrate the particles).
• Sound waves, ocean waves, waves on a rope are mechanical waves.
• The material that waves travel through is called the medium.
Mediums:• Sound waves travel through solids, liquids or gas.• Ocean waves travel through water.
Parts of a WaveIN A MECHANICAL WAVE,Amplitude shows how much energy a wave has.
If a sound wave has very little amplitude, the sound would be
Like a whisper or soft.
x-axis
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Parts of a waveWavelength is measured from crest to crest or
or trough to trough
Wavelength is measured in meters.
The crest is the highest point of a wave. The trough is the Lowest point of wave.
1 wave=A complete crestand a complete trough
Frequency of Waves• Frequency is the number of waves that
cross a point in a given amount of time.
• Measured in Hertz• 1 Hertz = 1 wave/sec A.
B.
Which has a higher frequency?A or B? a
Which has a higher amplitude?A or B? they are the same
Which has a greater wavelength?A or B? B
Calculate frequency
1 wave consists of 1 crest + 1 trough freq= # waves/ time it takes to pass a point
6 seconds here
Frequency = 3.5 waves/ 6 sec = .58 Hz
Types of Waves
1. Transverse Waves: waves where the matter in the medium moves back and forth at right angles to the direction that the wave travels
• Has crests and troughs
2. Compressional Waves: a type of wave where the matter in the medium moves back and forth in the same direction that the wave travels.
• Has compressions and rarefactions• Also called Longitudinal waves
Compression Wave
What is a rarefaction? Molecules spread out in a compression wave
What is a compression? Molecules compressed (squished together) in compression wave
Transverse Waves vs Compressional Waves
Examples of Transverse waves:1. Electromagnetic waves2. Ocean waves3. Wave on a rope
Examples of Compressional Waves:1. Sound waves
transverse
compressional
Transverse or Compressional?
com
pres
sion
com
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sion
rare
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rare
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Label,Wavelength,Amplitude, Crest andTrough
______________
_______________
INTERFERENCE
• Interference occurs when two (or more) waves are traveling through the same medium at the same time and interact.
Constructive Interference• When two waves combine to form in a way
that it produces a larger wave.
• Crest of one wave meets crest of another wave (or trough meets trough)
Larger wave
Destructive Interference• When two waves interact in a way that forms a
smaller wave.• When the crest of one wave meets the trough of
another wave
Example: Noise cancellingheadphones
Wave Behaviors
1. Reflection: when a wave strikes an object and bounces back.
• Examples: Mirror Image and Echoes
Reverberation below… bouncingOff walls and getting louder…(reflected sound wave)
Reflection of Waves
Echolocation….(Reflected sound)
SONAR… Sound Navigation and Ranging
(reflected sound wave)RADAR…. RAdio Detection And Range
(reflected Ewave)Seeing Colors (reflected Ewaves)
Wave Interactions2. Refraction: the bending of a wave caused by a change in speed due to a change in medium.• Examples: pencil looks bent in water, rainbow
Interaction of Waves
3. Diffraction: occurs when an object causes a wave to change direction and bends around it.
Light
Sound
Electromagnetic Waves• Created by vibrating electric charges• Can travel through a vacuum (needs NO medium to travel
through)• Have a wide variety of frequencies and wavelengths.• People can only see the wavelengths around 400 nanometers to 700 nanometers.• All travel at the speed of
light in a vacuum– 300,000 km/s – 670, 617, 000 mi/hr
Electromagnetic Spectrum• A device for organizing the
electromagnetic waves by frequency and wavelength.
Frequency and Waves• Higher frequency:
In E-waves: higher freq, higher energyIn Sound waves: higher freq, higher
pitchIn sound waves….• Humans can only hear sound waves
between 20 Hz and 20,000 Hz• Ultrasonic– above 20,000 Hz
bats, whales, dolphins, cats, dogs, ultrasound• Infrasonic– below 20 Hz
elephants
Doppler Effect• Change in pitch or frequency that occurs
when the source of a sound wave is moving relative to an observer.
Lower pitch sound Higher pitch sound(higher freq of waves)
ambulance.au
Doppler Effect
Doppler Shift
Speed of soundIn air…. 347 m/sIn water… 1498 /sIn aluminum… 4877 m/s
Terms
Intensity--- amount of energy that flows through a certain area at a certain time
Loudness– human perception of sound intensityDecibels– units to measure sound intensity or loudness
•Above 120 dB can cause pain in ears
Speed of Waves in different mediums
What happens to the speed of sound as it moves from a solid to liquid to gas?
Why? Slows down cause particles get farther apart and particles take longer to bump into each other and pass on energy.
What happens to the speed of light (ewaves) as it move from a solid to a liquid to a gas?
Why? Speeds up, ewaves don’t need a medium, particles just slow them down. They move fastest through a vacuum…. No medium.
Speed of Sound in different temperatures
What happens to the speed of sound as the temperature increases in a material?
Why? As temperature increases, speed of sound increases. Particles move faster and bump into each other more.
True or False?Sound waves move faster through cold air than hot air. _____Sound waves move faster through water than air. _________Radio waves move faster through air than a vacuum._______Sound waves move faster through a vacuum than air. _______
Gamma rays move faster than light waves through air. ______
Go to these websites and TAKE NOTES…
Doppler Effect:http://www.planetseed.com/files/flash/science/lab/airspace/doppler/en/doppler_exp.htm?width=750&height=460&popup=true
http://science.howstuffworks.com/dictionary/physics-terms/doppler-effect-info.htmDoppler Shift:http://zebu.uoregon.edu/~soper/Light/doppler.htmlSeeing Color: (Read and Watch Powerpoint)http://askabiologist.asu.edu/biology-bits/seeing-color-bits
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