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Transcript of Http://20Phy sics%20B%20II/course%20files/multimedia/lesson42/l essonp.html.
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http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson42/lessonp.html
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DefinitionWave: Any transfer of energy
without a transfer of matter
Wave Pulse: the disturbance that transfers energy
Periodic Wave: a series of identical, repeating evenly spaced pulses
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Medium: The substance through which waves pass or propagate
Transverse Wave: A wave in which a medium moves perpendicular to the direction of wave propagation
Longitudinal Wave: A wave in which a medium moves parallel to the direction of wave propagation
http://cnx.org/content/m12378/latest/Translong.swf
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Vibrations & Waves
http://www.stmary.ws/highschool/physics/home/notes/waves/Intro_wave_phenomena.htm
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Condensations: areas of maximum compressions; analogous to crests
Rarefactions: areas of maximum separation; analogous to troughs.
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Vibrations & WavesWavelength - Distance between peaks Amplitude - Max Height above resting spot
Related to the energy carried by the waveCorresponds to loudness in sound waves
and brightness in light waves Frequency - Number of Bounces/secondPeriod - Time of a complete vibrationPeriod = 1 / Frequency T = 1/fFrequency = 1 / Period
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Waves can be produced in two ways:a. Vibration of particles - this requires a medium for transfer
(mechanical wave)ex) sound, water wave, spring wave
b. Small changes in the strength of an electromagnetic field
- this requires no medium for transfer ex) light, microwaves, x-rays
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Pulses & Periodic Waves 1. Pulse – single vibratory disturbance that moves from point to
point (Medium only moves up and down)
Ex)In which direction will segment X move as the wave passes through it?
(1) down, only (2) up, only (3) down, then up, then down (4) up, then down, then up
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Pulses & Periodic Waves 1. Pulse – single vibratory disturbance that moves from point to
point (Medium only moves up and down)
Ex)In which direction will segment X move as the wave passes through it?
(1) down, only (2) up, only (3) down, then up, then down (4) up, then down, then up
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a.When the pulse (wave) reaches a boundary with another medium, part is reflected and part is transmitted (goes through)
From high speed to low speed (low density to high density)
From low speed to high speed (high density to low density)
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Reflection from a rigid boundary(reflected wave undergoes a 180o phase change)
Reflection from a free boundaryreflected wave has the same polarity (no phase change) as the incident wave
b. When a pulse reaches a fixed, unyielding boundary, then the pulse is completely reflected and inverted (180°)
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Wave characteristicshttp://www.stmary.ws/highschool/physics/ho
me/animations3/waves/Wave_Characteristics.html
http://www.stmary.ws/highschool/physics/home/animations3/waves/waves2.html
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Frequency exampleEx) A wave generator operating for 4 seconds
produces the waves drawn below.Top view of a periodic wave (Each line is a crest)
How many waves are drawn between A and B? (Be careful!!)
8 cycles
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exampleEx) A wave generator operating for 4 seconds
produces the waves drawn below.Top view of a periodic wave (Each line is a crest)
What is the frequency of this periodic wave train?
f = 8 cycles/4 sec = 2 cycles/sec = 2 Hz
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FrequencyIn Sound, frequency is pitch.
-Human Ear: Frequency Range 20 Hz - 20,000 Hz.
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter19/animation__effect_of_sound_waves_on_cochlear_structures__quiz_2_.html
In Light, frequency is color.
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Period T = 1/fPeriod (seconds) – time for an entire wave cycle to
pass a given point in a medium- determined by source of vibration not medium
Ex) The frequency of a light wave is 5.0 x 1014 hertz. What is the period of the wave?
T = 1/f = 1/(5.0 x 1014 hertz) = 2.0 x 10-15 s
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B (will take the longest to pass by)
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Amplitude Amplitude – maximum change in position of a
particle from its rest position during a single vibration
- determined by source of vibration, not medium
Amplitude of a wave shows the amount of energy in the wave
Amplitude is a measure of loudness for sound and brightness for color -
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"In Phase" (0°) – points on a single periodic wave that have the same displacement (from equilibrium position) and moving in the same direction
Whole number of wavelengths apartA & E, A & I, A & MB & F, B & J, B & N
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"Out of Phase"– (1800) - same displacement from equilibrium position but going in a different direction
½, 1½, 2½ etc wavelengths apartA & C, B & D, F & H
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C and F
Name 2 points that are 180° out of phase?
B and D E and G
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Wavelength λWavelength – distance between two consecutive
points in phasedetermined by medium λ = length of one cycle in meters / # of cycles
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Ex) Wavelength?
λ = 5.0 m/2.5 cycles λ = 2.0 m
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Ex) Amplitude? Wavelength?
Amplitude = .10 mWavelength = .60 m
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Ex) Amplitude A?, B?, C?
Amplitude of A = 2.0 mAmplitude of B = 2.0 mAmplitude of C = 1.0 m
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Speed: v = f λSpeed – the number of meters a single cycle
travels per second
Speed of wave depends on the medium
(slower in dense media)
http://www.stmary.ws/highschool/physics/home/review/outsideContent/waves/speedMechanical_wave.htm
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Speed: v = f λSpeed – the number of
meters a single cycle travels per second
Solve for f : f = v / λ
Frequency and
Wavelength are INVERSELY RELATED
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Ex) f = 40. hertz. V = ?
(1) 13 m/s (2) 27 m/s(3) 60. m/s (4) 120 m/s
V = fλ
V = 40. Hz(1.5 m) (3) 60. m/s
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Hw Pg 153-155 #1 - 47
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VelocityVelocity sound = 3.3 x 102 m/s(Air, Reference Table, room temperature)
Velocity light in a vacuum = 3 x 108 m/s
About how many times faster is light than sound?
About 1 million times
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Depends on the material of the vibrating medium
Sound can vibrate water, wood (speaker enclosures, pianos), metal, plastic, etc.
Sound speed in dry air is 330 meters/second at 0o C
Faster in warm air, slower in coldWater 4 times faster, steel 15 times faster
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Source MediumFrequency Speed
Period Wavelength
Amplitude
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Doppler Effecthttp:/0/science.discovery.com/videos/time-do
ppler-effect.htmlSheldon explains:
http://www.youtube.com/watch?v=Y5KaeCZ_AaY
http://www.stmary.ws/highschool/physics/home/animations3/waves/DopplerEffectTrain.html
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Doppler EffectDoppler Effect – variation in the observed
frequency of a wave when there is relative motion between the source of the wave and the receiver
Because car is “driving into it’s sound wave” the observer in front of car hears a higher frequency.An observer behind the car hears a lower frequency.
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To the right, wherethe frequency is higher
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Doppler effect on electromagnetic wavesFor Electromagnetic waves, such as visible
light, the frequency change is recorded as a color shift.
Astrophysicist site this phenomenon as proof that universe is expanding.
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Sonic BoomOr
- What happens when you go faster than the speed of sound
http://www.metacafe.com/watch/1956849/sonic_boom/
Interesting Fact:The crack of a whip is the sound of the
tip breaking the speed of sound.
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Wave Front– locus of adjacent points on a wave which are in
phaseTop View
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Superposition Superposition – when waves overlap, the
resultant displacement is the algebraic sum of the individual displacements of each wave – This causes interference
http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson42/lessonp.html
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Interference– effect produced by two waves passing
simultaneously through a region
There exist two kinds of interference:1.Constructive interference 2.Destructive interference
http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson46/lessonp.html
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As the two waves belowpass through eachother, the medium atpoint P will …
(1) vibrate up and down (2) vibrate left and right (3) vibrate into and out of the page(4) remain stationaryJune 2004
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As the two waves belowpass through eachother, the medium atpoint P will …
(1) vibrate up and down (2) vibrate left and right (3) vibrate into and out of the page(4) remain stationaryJune 2004
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What will the amplitude of the resultant wave be when wave A and B meet at point X?
Amp A + Amp B = 2 + -1 = +1
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What is the amplitude of the wave producedwhen these waves overlap?
15 cm
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Symmetrical Lines of Interferencehttp://www.stmary.ws/highschool/physics/ho
me/animations3/waves/interference.swfwave patterns produced by the overlap of 2
wave fronts in phaseMaximum Constructive Interference – Phase
difference – whole wavelengthMaximum Destructive Interference -
Phase Difference - 1/2 wavelengthhttp://techtv.mit.edu/tags/1750-interference/v
ideos/632-mit-physics-demo----microwave-interference
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Destructive Interference
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http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/
multimedia/lesson44/lessonp.html
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Standing Waveshttp://www.stmary.ws/highschool/physics/
home/animations3/standingWaves.swf
Standing Wave – waves produced when two waves of the same frequency and amplitude travel in opposite directions in the same medium (ex. Musical instruments)
http://video.google.com/videoplay?docid=5614877943718237184#docid=6482474251978139047
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definitionsAntinode – The point of maximum
displacement of a medium
Node – Regions of zero displacement of the medium.
Caused by maximum destructive interference
Standing waves can also be created by reflection
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How many Nodes?
5
How many antinodes?
4
How many waves?
2
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http://www.physicsclassroom.com/Class/waves/U10L4e.cfm
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Periodic Wave PhenomenaBeats and resonance
http://video.mit.edu/watch/tuning-forks-resonance-a-beat-frequency-11447/
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BeatsOccur when two sound waves of nearly the same
frequencies (ex. 256Hz and 258 Hz) interact with one another
Beat Freq: Larger freq – smaller freqPitch of resulting soundwave is the average of the two
freq.
In our example f1 = 256 Hz f2 = 258 Hz
Beat Frequency : f2 - f1 = 258 Hz – 256 Hz = 2 beats / sec
Pitch = avg. freq = f2 + f1 = 258 Hz + 256 Hz = 257 Hz
2 2
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When the forced vibration matches a natural frequency we get a “resonance” condition
Think about a swing on a playgroundYou go high when you pump the swing
at its natural vibration frequencySympathetic vibrations in tuning forksFamous Tacoma Narrows bridge
collapsehttp://videos.howstuffworks.com/tlc/29833-understanding-
tacoma-narrows-bridge-video.htm
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ResonanceResonance – Building up of energy by
adding small amounts of energy in time with the natural frequency of an object
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Resonance FrequencyResonance Frequency – natural
frequency that an object vibrates when disturbed
Can sound be used to break glass? Great video!
http://techtv.mit.edu/videos/2964-breaking-glass-with-sound
http://www.youtube.com/watch?v=BE827gwnnk4
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http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson46/lessonp.html
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Diffraction – the spreading out of a wave into the region behind an obstacle
Amount of Diffraction depends on Wavelength & Size of Slit.
Diffraction increaseswhen size of the slit approaches wavelength size.
http://www.stmary.ws/highschool/physics/home/notes/waves/WaveBehavior/diffractionSlitD.swf
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hwPg 159 – 161 #48-71
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When a sound wave reflects from a surface we generate an echo
Wave reflection from surfaces depends on the characteristics of the surface
Smooth hard surfaces reflect bestRough soft surfaces reflect poorlyEnergy not reflected is absorbed or
transmitted through the material
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Think of arrows pointing in the direction of the wave motion
We can trace the path of these arrowsAngle of incidence = Angle of reflection
(θ1=θ2)
Angles Equal
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Acoustics of room design is very interesting. Need some reflections to “liven” the room. Too many reflections and the sound gets mushy. Look in a concert hall or auditorium to see the different sound treatments
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If there is a change in the characteristics of a medium, waves are bent
This occurs because different parts of the wave front travel at different speeds
Think of a marching around a curved track
The inside people have to move more slowly than the outside people to keep the lines straight
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The combination of reflection and refraction enables imaging
Ultrasonic medical imagingNaval SONAR for detecting
submarinesBats catch mosquitoes