2A wave is a vibratory disturbance that propagates through a medium (body of matter) or field. Examples of waves: sound, light, water waves, microwaves.
3Waves and Energy Transfer Waves transfer energy from one place to another by repeated small vibrations of particles.Waves ONLY transfer energy NOT mass.Notice that all the matter is in the same place after the wave has passed.
4Wave TypesMechanical Waves: need a medium to travel through (air or water).Sounds wavesWater waves
5Wave Types2. Electromagnetic Waves: do not need a medium to travel through and can travel through a vacuum.Radio wavesLight waves
6Types of Wave MotionLongitudinal Wave: a wave in which the motion of the vibration is parallel to the direction of wave travel.Ex. Sound waves,compression wavesin a spring, andearthquake P-waves.
7Direction of wave motion SourceOfSoundWaveThis is how energy is transferred for a sound wave. Notice the individualparticles remain in the same location after the wave passes by. Also notice thatthe direction of motion of the wave and the direction of particle motion is parallelto each other.
8This is how energy is transferred by compressing a spring or slinky.
9This is how energy is transferred through the earth with an earthquake P-wave. Notice the black square, it starts and endsin the same location showing us how waves transferenergy NOT matter.
10Types of Wave MotionTransverse Wave: a wave in which the motion of the vibration is perpendicular to the direction of wave travel.ParticleMotionWave MotionEx. Electromagnetic waves (light), earthquake S-waves.
11This is how energy is transferred in a transverse wave. ParticleMotionWave MotionThis is how energy is transferred in a transverse wave.Fix your eye on one of the particles. Notice it’smovement as the wave passes by. It moves up,then down, then back up again. This movementis perpendicular to the wave motion.
12This is how energy is transferred through the earth with an earthquake S-wave. Notice the black square, it moves up,then down, then back up to it’s original position showing us that onlyenergy is transferred NOT matter.
13Unlike longitudinal waves, transverse waves can be oriented in many different planes.
14Pulses vs. Periodic Waves A pulse is a single short disturbance or wave that moves from one place to another.The speed of the pulse depends on the medium.
15If a rope with a traveling pulse is attached to a fixed unyielding object, like a wall in the picture below, the pulse will be reflected.Reflection is therebounding of a pulseor wave as it strikesa barrier.
16What specifically happens to the pulse when it hits the wall? Remember Newton’s 3rd Law?When the pulse arrives at the wall it exertsan upward force on the wall. The wall thenexerts a force that is equal in magnitude(size of the wave doesn’t change) butopposite in direction. This reaction invertsthe pulse.
17As a pulse reaches a new medium, part of the pulse is transmitted through the medium, part is absorbed, and part is reflected back towards the source.Low Density Medium to High Density MediumReflected wave is inverted, transmitted wave is slower.
18High Density Medium to Low Density Medium Reflected wave is upright, transmitted wave is faster.
19A periodic wave is a series of pulses or evenly timed disturbances.
20Characteristics of Periodic Waves The complete series of changes (one complete vibration) at one point in a medium as a wave passes is called a cycle.Here particles move forward and then back as the wave passes.This forward-back motion is one cycle.
21Here particles move up, down, then back to it’s original position as the wave passes.This up-down-up motion is one cycle.
22Frequency (f): # of cycles per second A frequency of 1 cycle per second is called 1 hertz (Hz).1 Hz = 1s
23Sound Waves and Frequency The frequency of a sound wave determines the pitch.
24Light Waves and Frequency The frequency of a light wave determines its color.
25Try this… f = 10 cycles 5 seconds = 2 cycles 1 second = 2 Hz 10 wave cycles pass a fixed point in a medium in 5 seconds. What is the frequency (cycles per second) of the wave?f = 10 cycles5 seconds= 2 cycles1 second= 2 Hz
26Frequency of the Human Ear Humans can detect frequencies in the range of 20 to 20,000 Hz.How does the human ear work?
27The frequency tells us how many cycles per second travel through a medium. Sometimes we just want to know the time it takes to complete only 1 cycle. This is the period (T) of a wave.T = 1f
28Try this…The frequency of a wave is 2 hertz. What is the period of the wave?T = 1f= 12 Hz= .5 sIt takes .5 s for one complete wave cycle topass by a point in a medium.
29Try this…The frequency of a light wave is 5.0 x 1014 hertz. What is the period of the wave?T = 1f=5.0 x 1014 Hz= 2.0 x s
30Which wave has the longest period (would take the longest time for one cycle to pass)?
32The amplitude of a wave shows the amount of energy in a wave. With sound waves amplitude is represented by loudness. Sound waves with large amplitudes are loud.With light waves amplitude is represented by brightness. Light waves with large amplitudes are brighter.
34Wavelength (λ) Longitudinal Transverse A wavelength is the distance between any two successive points in the same position on a wave. It’s the length of one complete wave cycle.λλLongitudinalTransverse
35What is the λ of the wave train below? 5 m2.5 waves= 2 m
36Find the amplitude and λ for the series of waves below. Amplitude = .1 m
37Wave PhaseCertain parts of a single wave have a phase associated with it.Let’s start by looking at a circle:90°0°180°360°270°
38Points on successive waves that are in the same position on the wave (360° apart or 1 wavelength apart) are said to be “in phase.”360°/λ
39Which two points are in phase with each other? C and F
40Which 2 points are 180° out of phase? 1 λ2B and D, or E and G
41Immediately after the wave moves through point A , will point B move up, down, left, or right? Before you answer any question like this make sure you re-draw the wave after it has moved.BAB would move up
42Speed of Waves v = fλ λ = v f Inverse relationship- if a From this equation what is the relationship between frequency and wavelength?λ = vfInverse relationship- if awave has a high frequencythen it is going to have asmall or short wavelength.
43Find the velocity of the wave below if it has a frequency of 40 Hz. v = fλv = 40 Hz(1.5 m)v = 60 m/s
44The speed of a wave depends upon its type and the medium through which it travels.
46Sound vs. Light Waves Speed of Sound – 331 m/s (3.31 x 102 m/s) Remember sound and light waves are different types of waves. Sound – longitudinal. Light – transverse. Therefore they travel differently and at different speeds.Speed of Sound – 331 m/s (3.31 x 102 m/s)Speed of Light – 300,000,000 m/s (3.00 x 108 m/s)Light is 1 million times faster than sound!
47This is why you “see” lightning before you “hear” it. You can approximate the storms distance in miles by counting the seconds between the lightning and thunder. Every 5 seconds is approximately 1 mile.
48and arrives before the sound does. When a source, this time something like a fighter jet, travels at a speed greater than thespeed of sound, it actually outruns the sound waves, and is said to break the sound barrier,and arrives before the sound does.
49Try this…The following diagram shows a segment of a periodic wave in a rope traveling to the right to point G.What type of wave is represented in the diagram?What is the amplitude of the wave?What is the wavelength of the wave?If the frequency of the wave is 2 Hz, what is the period of the wave?Determine the speed of the wave.Name the two points on the wave that are in phase.Immediately after the wave moves through point g, will point B move up, down, left, or right?2.4 m6.0 m
50Wave FrontsIn a 3-dimensional medium such as air, waves radiate in concentric spheres from a vibration point.Wavefronts/CrestsTroughs
52Doppler EffectWhen wave fronts are in motion observers will find an APPARENT change in frequency of the wave.Remember how frequency is represented in a sound wave?PITCHRemember how frequency is represented in a light wave?COLOR
53Let’s take a closer look: A wave source not in motion will radiate waves out in all directions equally.If the source of the wave is approaching an observer (or the observer is approaching the wave source) the frequency APPEARS to increase.An ambulance, with it’s siren on, is a moving source ofsound waves. Notice now that the wave fronts are notequally spaced. The waves toward the front of theambulance where the observer is appear closer togetherthis means they appear to have aHIGHER FREQUENCY/SHORTER WAVELENGTH.HIGHER FREQUENCY EQUATES TO A HIGHER PITCHED SIREN.
54If the source of the wave is leaving an observer (or the observer is leaving the wave source) the frequency APPEARS to decrease.The waves toward the back of the ambulance where theobserver is appear further apart. This means they appearto have a LOWER FREQUENCY/LONGER WAVELENGTH.LOWER FREQUENCY EQUATES TO A LOWER PITCHED SIREN.
55So as an ambulance approaches and then passes you the sound of the ambulance’s siren drops in pitch.
56The effects are similar with light waves except we don’t hear the effects we see them. BLUE-SHIFTRED-SHIFTA light sourceapproaching youappears to have ahigher frequency/shorter wavelengthand will appearblue in color.A light sourcemoving away from youappears to have alower frequency/longer wavelengthand will appearred in color.
57Applications of the Doppler Effect Weather Forecasting:Radar bounces radio waves off water particlesin clouds. A computer measures how long ittakes for the waves to reflect back and thenuses the time to calculate how far the particleis away from the radar.Doppler radar can also calculate if a raindrop ismoving toward or away from the radar.Meteorologists know that if the rain is moving,then the wind must be pushing it. That's howthey can tell where the wind is blowing inclouds.
58Applications of the Doppler Effect: Radar Gun:When radio waves emitted from a radar gunhit an object that is moving toward the patrolvehicle, the returning frequency will be higherthan the original. When the signal hits thatvehicle that is moving away from the observer,the returning frequency will be lower thanthe original one. The frequency change can beused to determine the speed of the target vehicle.
60Interference: effect produced by two waves passing simultaneously through a region. What happens when waves interfere with each other?The principle of superposition states that the combined displacement of the two interfering waves is the algebraic sum.
61Constructive Interference The combination of two waves in the same phase.
69Wave fronts and Constructive/Destructive Interference Here 2 crests/troughs are coming together =maximum constructive interferenceWave fronts/crestsHere a trough and a crest arecoming together =maximum destructive interferencetroughs
70All along here there is max constructive interference All along here there is max destructive interference-there is no effect from either waveWave tank
71Standing WavesWhen two waves having the same amplitude and frequency travel in opposite directions a standing wave is formed.
72Antinodes- the points of maximum displacement when two waves are interacting.Nodes- the points of zero displacementwhen two waves are interacting.
73The nodes and antinodes are stationary and the wave appears to stand still.
745 4 2 How many nodes are on this standing wave? How many antinodes are on this standing wave?How many waves make up this standing wave?2
75How many wavelengths for each of these standing waves? ½ λ1 λ1 ½ λ2 λ2 ½ λ3 λ3 ½ λ
76How many wavelengths make up this standing wave. How many nodes How many wavelengths make up this standing wave? How many nodes? How many antinodes?
77ResonanceNatural Frequency- every elastic object has a particular frequency at which it will vibrate at if struck.If we strike a tuning fork to make it vibrate at itsnatural frequency of 512 Hz, then place it near anidentical nonvibrating tuning fork, the nonvibratingtuning fork will resonate due to the vibration.This is REASONANCE.
78Opera Singer shattering glass? Really? Just like the tuning fork, a glass has a natural frequency at which it will vibrate. It is possible for an opera singer to shatter a glass by maintaining a note with a frequency equal to the natural frequency of the glass.
79The transfer of energy by resonance increases the amplitude of vibrations in the glass until its structural strength is exceeded.
80Tacoma Narrows Bridge, 1940High winds set up standing waves in the bridge in addition to vibrations in a torsional (twisting) mode. Resonance increased the amplitude of vibrations until the bridge collapsed.
81DiffractionDiffraction is the spreading out of a wave into a region beyond an obstacle.
82The wavelength ofthese waves……is the same as thewavelength of thesewaves.
83The amount of diffraction depends on the wavelength and size of opening. Ripple Tank
84Which size slit will cause a wave to diffract the most?
86Double Slit Diffraction- if we use light waves we will see a pattern (fringes) appear on a nearby screen.
87Not the pattern you might expect…this shows us INTERFERENCE again.
88Because the waves emanating from the two slits were originally from the same source, they always keep in step with each other. At the screen this results in bands of light where reinforcement is occurring and dark where cancellation is occurring. These bands or 'fringes' are called a diffraction pattern. The distance between the fringes y = λD/a where λ = the wavelength of the light, D = the distance from the slits to the screen and 'a' = the distance between the slits.