Presentation on theme: "Waves Carry Energy, not Matter"— Presentation transcript:
1Waves Carry Energy, not Matter A wave is a repeating disturbance that transfers energy through matter or space.Waves carry energy from one place to another.When waves travel through solids, liquids, and gases, matter is not carried along with the waves.Waves carry energy without transporting matter.
2Types of WavesAll waves are produced by something moving back and forth, or vibrating.It is the energy of the vibrating object that waves carry outward.Some waves, known as mechanical waves, can travel only through matter.The material through which a wave travels is called the medium .Waves called electromagnetic waves can travel either through matter or through empty space.
3Transverse WavesA transverse wave causes particles in matter to move back and forth at right angles to the direction in which the wave travels.High points in the wave are called crests. Low points are called troughs.The series of crests and troughs forms a transverse wave.
4Compressional WavesAnother type of mechanical wave is a compressional wave.A compressional wave causes particles in matter to move back and forth along the same direction in which the wave travels.
5Compressional WavesThe places where the coils are squeezed together are called compressionsThe places where the coils are spread apart are called rarefactions. The series of compressions and rarefactions forms a compressional wave.
6Waves1Combination WavesSeismic waves move through the ground during an earthquake.Some of these waves are compressional, and others are transverse.The seismic waves that cause most damage to buildings are a kind of rolling waves.
7Electromagnetic Waves Light, radio waves, and X rays are examples of electromagnetic waves.Electromagnetic waves are transverse waves.They contain electric and magnetic parts that vibrate up and down perpendicular to the direction the wave travels.
8Properties of WavesThe properties that waves have depend on the vibrations that produce the waves.For example, if you move a pencil slowly up and down in a bowl of water, the waves produced by the pencil’s motion will be small and spread apart.
9WavelengthThe distance between one point on a wave and the nearest point moving with the same speed and direction is the wavelength.The wavelength of a transverse wave is the distance between two adjacent crests or two adjacent troughs.
10WavelengthThe wavelength of a compressional wave is the distance between two adjacent compressions or rarefactions.
11FrequencyThe frequency of a wave is the number of wavelengths that pass by a point each second.If you were watching a transverse wave on a rope, the frequency of the wave would be the number of crests or troughs that pass you each second.
12Period and Frequency (P297) Frequency (f) of a wave is the number of wavelengths that pass a fixed point each second.SI Unit is hertz (Hz) 1 Hz = 1 wave/secPeriod (T) of a wave is the amount of time it takes one wavelength to pass a pointSI Unit is sec/wavelengthf= 1/T and T= 1/f
13Amplitude of a Transverse Wave The amplitude of a transverse wave is half the distance between a crest and trough.As the distance between crests and troughs increases, the amplitude of a transverse wave increases.
14Amplitude of a Compressional Wave The amplitude of a compressional wave depends on the density of material in compressions and rarefactions.
15Amplitude and EnergyThe vibrations that produce a wave transfers energy to the wave.The more energy a wave carries, the larger its amplitude.Amplitude of waves relate to the energy of the wave.
16Review- Nature of Waves Wave- a repeating disturbance or movement that transfers energy through matter or space.Molecules pass energy on to other moleculesWaves carry energy without transporting matterAll waves are produced by something vibratingMedium – a material through which a wave travelsMechanical WavesTravel only through matterTransverse waves matter moves perpendicular to direction wave moves- wave in a string or slinkyCompressional waves matter moves in the same direction that the wave moves.- sound waves
17Review- Wave Properties Waves differ-How much energy they carryHow fast they travelHow they lookTransverse waves have crests and troughsCompressional waves have dense regions called compressions and less dense regions called rarefaction
18Wave PropertiesWave length- the distance between one point in the wave and the next corresponding partFrequency- how many waves pass a fixed point each secondExpressed in hertzAs frequency increases, wavelength decreasesThe frequency of a wave equals the rate of vibration of the source that creates it.
20Wave SpeedThe speed of a wave depends on the medium in which the wave travels.You can calculate the speed of a wave if you know its wavelength and frequency using this equation.Wave Speed Equationwave speed (m/s) = wavelength (m) X frequency (Hz)v= λf
21Wave SpeedIn this equation, v is the symbol for wave speed and f is the symbol for frequency.The SI unit for frequency is the hertz, abbreviated Hz. One hertz equals one vibration per second, or one wavelength passing a point in one second.The wavelength is represented by the Greek letter lambda, λ, and is measured in meters.
22Problems P299Example: What is the speed of a sound wave that has a wavelength of 2.00m and a frequency of Hz?V= fλAssignment Page 299: 1-4
23Amplitude Amplitude is a measure of the energy in a wave The more energy a wave carries, the greater the amplitude.Amplitude of compressional waves is related to how tightly the medium is pushed together at the compression.The more dense the compression, the larger the amplitude is and the more energy the wave carries.The less dense the rarefactions, the higher the amplitude and the more energy the wave carries
24Amplitude of transverse waves The distance from the crest or trough of a wave the rest point of the medium.Example: how high an ocean wave appears above the water level.
25Waves Can Change Direction or Amplitude (p 304-306) Waves don’t always travel in the same straight line.Waves can change direction when they travel from one material to another or when they strike some media.All waves can reflect (bounce off a surface), refract (change direction), or diffract (bend around an obstacle).Waves can also change amplitude when they pass through another wave, this is referred to as interference.
26The Law of ReflectionAccording to law of reflection, the angle that the incoming wave (incident) makes with the normal equals the angle that the outgoing (reflection) wave makes with the normal.Incident angle= Reflection angleθrθiθi=θr
27Refraction When a light wave moves from air to water, it slows down. This change in speed causes the light wave to bend.Refraction is the change in direction of a wave caused by a change in its speed as it movers from one material to another.
28RefractionThe greater the change in speed is, the more the wave bends.When a wave passes into a material that slows it down, the wave is bent toward the normal.When a wave passes into a material that speeds it up, the wave is bent away from the normal.
29DiffractionWaves can change direction by diffraction, which is the bending of waves around an object.The amount of diffraction or bending of the wave depends on the size of the obstacle the wave encounters.If the size of the obstacle is much larger than the wavelength, very little diffraction occurs.If the size of the obstacle is much smaller than the wavelength, the wave diffracts a lot.
30Diffraction of Sound and Light The wavelengths of sound waves are similar to the size of objects around you, but the wavelengths of light waves are much shorter.As a result, you can hear people talking in a room with an open door even though you can’t see them.
31InterferenceWaves can also change amplitude when they pass through another wave, this is referred to as interference.Interference is the ability of two or more waves to combine and form a new wave.Waves pass right through each other and continue in their original direction.New wave exists only while the two original waves continue to overlap.
32Interference Superposition Principle Constructive Interference In Phase½ λDestructive Interference Out of Phase
33Standing Waves (p310,334)Standing wave- a special type of wave pattern that forms when waves of equal wavelength and amplitude, but traveling in opposite directions, continuously interfere with each other. Standing waves form a pattern that stays in one place.Node – the place where two waves always cancel each other.Fundamental frequency the main tone that is heard when something vibrates.Overtone is a vibration whose frequency is a multiple of the fundamental frequency.
34Resonance (p311)Resonance is the process by which an object is make to vibrate by absorbing energy at its natural frequency.Resonance is the ability of an object to vibrate by absorbing energy at its natural frequency.
35Waves Carry Energy, not Matter A wave is a repeating disturbance that transfers energy through matter or space.Waves carry energy from one place to another.In water waves, the energy is transferred by water molecules.When waves travel through solids, liquids, and gases, matter is not carried along with the waves.Waves carry energy without transporting matter.
37Types of WavesAll waves are produced by something moving back and forth, or vibrating.It is the energy of the vibrating object that waves carry outward.Some waves, known as mechanical waves, can travel only through matter.The material through which a wave travels is called the medium .Waves called electromagnetic waves can travel either through matter or through empty space.
38Amplitude of a Transverse Wave The amplitude of a transverse wave is half the distance between a crest and trough.As the distance between crests and troughs increases, the amplitude of a transverse wave increases.
39Wave SpeedThe speed of a wave depends on the medium in which the wave travels.You can calculate the speed of a wave if you know its wavelength and frequency using this equation.Wave Speed Equationwave speed (m/s) = wavelength (m) X frequency (Hz)v= λf
40Waves Can Change Direction or Amplitude (p 304-306) Waves don’t always travel in a straight line.Waves can change direction when they travel from one material to another or when they strike some media.All waves can reflect (bounce off a surface), refract (change direction), or diffract (bend around an obstacle).Waves can also change amplitude when they pass through another wave, this is referred to as interference.
41Making Sound WavesVibrations transfer energy to nearby air particles, producing sound waves in air.Every sound you hear is caused by something vibrating.For example, when you talk, tissues in your throat vibrate in different ways to form sounds.
42Sound Waves are Compressional Waves Sound waves are formed when a vibrating object collides with air molecules, transferring energy to them.Sound waves produced by a vibrating object are compressional waves.A vibrating drum head produces a sound wave.The drum head produces a compression each time it moves upward and a rarefaction each time it moves downward.
43Sound Waves are Compressional Waves Sound waves can only travel through matter.Medium- the type of matter whether liquid, solid or gas; that sound waves travel through.The energy carried by a sound wave is transferred by the collisions between the particles in the material the wave is traveling in.
44The Speed of SoundA sound wave’s speed depends on the medium through which it travels.Sound waves travel more quickly through solids and liquids because the molecules are closer together than in a gas.The speed of sound through a material increases as the temperature of the material increases.
45Problems (d=vt)A cannon flash is seen, but it takes 6 seconds for the sound to reach the persons ear. How far away was the cannon?A ship 1200 meters off shore fires a gun. How long after the gun is fired will it be heard on the shore?A drummer hits a cymbal and 10 seconds later hears the echo of the sound from a distant mountain. How far away was the mountain?
46Perception and Physical Measurement The human ear interprets the physical characteristics of the sound waves.
47The Loudness of Sound What makes a sound loud or soft? The difference is the amount of energy.Loud sounds have more energy than soft sounds.The amount of energy a wave carries corresponds to its amplitude which is related to the density of the particles in the compressions and rarefactions.
48IntensityThe amount of energy that a wave carries past a certain area each second is the intensity of the sound.The intensity of sound waves is related to the amplitude. Loudness is the human perception of sound intensity.This figure shows how the intensity of sound from the cymbals decreases with distance.
49The Decibel Scale and Loudness The intensity of sound waves is measured in units of decibels (dB).The softest sound a person can hear has an intensity of 0 dB.Sound with intensities of about 120 dB or higher are painful to people.
50The Decibel Scale and Loudness Loudness is the human perception of the intensity of sound waves.Each increase of 10 dB in intensity multiplies the energy of the sound waves ten times, 20 dB multiplies by 100, 30 dB by 1000 times.Most people perceive this as a doubling of the loudness of the sound.
52Frequency and PitchThe frequency of sound waves is determined by the frequency of the vibrations that produce the sound. Frequency is the number of compressions or rarefactions of a sound wave that passes per second,People are usually able to hear sounds with frequencies between about 20 Hz and 20,000 Hz.Pitch is the human perception of the frequency of sound, how low or high a sound seems to be..Sounds with low frequencies have low pitch and sounds with high frequencies have high pitch.
53Ultrasonic Ultrasonic waves are sound frequencies over 20,000 Hz. Ultrasonic waves have medical and scientific uses.Infrasonic or subsonic waves with frequencies below 20 Hz usually can’t be heard but may feel a rumble.
54Doppler EffectThe change in pitch or wave frequency due to a moving wave source is called the Doppler Effect.See page 331
55Doppler Effect Sounds moving toward a listener rise in pitch while sounds moving away from a listener lower in pitch.V=f λλλff
56The Reflection of Sound Echoes are sounds that reflect off surfaces.Repeated echoes are called reverberation.The reflection of sound can be used to locate or identify objects.Echolocation is the process of locating objects by bouncing sounds off them. (Sonar)
57Echo Distance from source Persistence of human ear 1/10 secondSpeed of sound 340 m/sDistance =Wavelength of sound less than height of reflecting bodyIntensity of the sound sufficient to be heard after the reflection
58Noise vs Music Music is pleasant to the ear Regular patterns No sudden changes inloudnessfrequencywavelength
59Sound Summary Sound is produced by the vibration of some object drum headStringmetal tuning forkcolumn of airSound travels by waves but only in matterSound waves are compressional wavesSpeed of SoundSound travels only in matterSound travels fastest in solids, slowest in gasesSound travels faster at higher temperatures
60Sound Summary Amplitude of Sound Waves Frequency of Sound Waves Amplitude is a measure of the energy of the waveIntensity is the energy divided by the areaIntensity is measured in decibelsThe human ear can safely hear sounds with intensity between 0 db and about 120 dbLoudness is how the human ear perceives intensityFrequency of Sound WavesFrequency is vibrations per second (Hz)Pitch is how the human ear perceives frequencyThe human ear can detect sounds between 20 Hz and 20,000 Hz
61Waves in Empty SpaceLight from the Moon has traveled through space that contains almost no matter.You can see light from the moon, distant stars, and galaxies because light is an electromagnetic wave.
62Electromagnetic Waves Light, radio waves, and X rays are examples of electromagnetic waves.Electromagnetic waves can travel through space or through matter.Electromagnetic waves are transverse waves.They contain electric and magnetic parts that vibrate up and down perpendicular to the direction the wave travels.
63Producing Electromagnetic Waves Magnetic waves are made by vibrating electric charges.Electric and magnetic fields are related forces that operate even in empty space.A moving electric charge produces a magnetic fieldA changing magnetic field creates an electric field.
64Producing EM Waves (cont) Electromagnetic waves are produced when an electric charge is vibrating.Vibrating electric charges are surrounded by vibrating electric and magnetic fields.Vibrating electric and magnetic fields travel outward from the moving charge.
65Properties of Light Waves An electromagnetic wave contains an electric part and a magnetic part.Both parts are called fields and vibrate at right angles to the wave motion.
66EM waves are transverse waves EM waves carry radiant energyEM waves are characterized by frequency, wavelength and velocity.V= λ fSpeed of light is a constant in any mediumAs frequency increases, wavelength decreasesFrequency is the number of vibrations per secondWavelength is the distance between crests
67The Speed of LightIn empty space (vacuum), light travels at a speed of about 300,000 km/s.Light travels so fast that light emitted from the Sun travels 150 million km to Earth in only about eight and a half minutes.When light travels in matter, it interacts with the atoms and molecules in the material and slows down.As a result, light travels fastest in empty space, and travels slowest in solids.
68Wavelength and Frequency of Light Wavelengths of light are usually expressed in units of nanometers (nm).One nanometer is equal to one billionth of a meter.Green light has a wavelength of about 500 nm, or 500 billionths of a meter. A light wave with this wavelength has a frequency of 600 trillion Hz.
69Intensity of Light Waves The intensity of waves is a measure of the amount of energy that the waves carry.For light waves, the intensity determines the brightness of the light.A dim light has lower intensity because the waves carry less energy.
70The Electromagnetic Spectrum The electromagnetic spectrum is the complete range of electromagnetic wave frequencies and wavelengths.
71The Electromagnetic Spectrum At the other end of the spectrum the waves have high frequency, short wavelength, and high energy.
72The Electromagnetic Spectrum At one end of the spectrum the waves have low frequency, long wavelength, and low energy. At the other end the waves have high frequency, high energy and short wavelengths.Short WavelengthLong WavelengthLow FrequencyLow EnergyHigh FrequencyHigh Energy
73Speed, Wavelength, Frequency Speed = frequency x wavelengthV= f λfrequency increases- wavelength decreasesfrequency decreases- wavelength increases
74Radio Waves and Microwaves The wavelengths of radio waves are greater than about 0.3 meters.Some are even thousands of meters long.The shortest radio waves are called microwaves.These waves have a wavelength between about 0.3 meters and meters.
75Infrared WavesInfrared waves have wavelengths between meters and 700 billionths of a meter.All warm bodies emit infrared waves.Law enforcement officials and military personnel sometimes use special night goggles that are sensitive to infrared waves. These goggles can be used to help locate people in the dark.
76Visible Light and Color The range of electromagnetic waves between700 and 400 billionths of a meter is the range of wavelengths people can see.
77Ultraviolet WavesElectromagnetic waves with wavelengths between about 400 billionths and 10 billionths of a meter are ultraviolet waves.Ultraviolet waves carry more energy than visible light waves.Sunlight that reaches Earth’s surface contains a small fraction of ultraviolet waves.
78X Rays and Gamma RaysThe electromagnetic waves with the highest energy, highest frequency, and shortest wavelengths are X rays and gamma rays.X rays pass through soft tissues, but are blocked by denser body parts, such as bones.
79X Rays and Gamma Rays Gamma rays are even more energetic than X rays. One use of gamma rays is in the food industry to kill bacteria that might increase the rate of spoilage of food.
80Electromagnetic Waves from the Sun Most of the energy emitted by the Sun is in the form of ultraviolet, visible, and infrared waves.Only a tiny fraction of this energy reaches Earth.
81Schedule Topic Assignment Tue 2/1 Waves, Wave Measurements Read p Worksheet Section 1&2,Wed 2/2Wave behaviorRead p , Problems P299Thur 2/3Wave behavior-superpositionRead p Complete Note taking worksheetFri 2/4Chapter 10 ReviewCh 10 Review Page 316:9-16, 17, 27-29Mon 2/7Sound wavesRead p , Sound worksheetTue 2/8Chapter 11 ReviewPage 348: 8-17Wed 2/9Electromagnetic wavesRead p , EM waves worksheetsThur 2/10Electromagnetic SpectrumRead pFri 2/11LightRead p , Light worksheetMon 2/14Optics LabComplete lab and all worksheetsTue 2/15ReviewMirrors and Lens NTWSWed 2/16TestTurn in all HomeworkThur 2/17
82Seeing is Reflecting Page 384 To see an object:It must produce lightOr Reflect lightAll objectsReflect lightAbsorb lightSome Transmit light (refract)
83Matter and Light Absorb, Reflect, Refract (transmit) Materials that absorb and reflect light are called opaque.Materials that refract and absorb light irregularly are called translucent. Translucent materials allow some light to pass through.Materials that refract (transmit) most of the light are called transparent.
84Reflected Light Page 385Reflection- a light wave strikes an object and bounces off.Angle of reflection = angle of incidenceRegular Reflection – mirrors – reflect light in single direction and form sharp images.Diffuse Reflection- irregular surfaces like brick walls reflect light in many different directions and do not form an image.We see objects because they reflect light.
85Refracted Light PageRefraction- change in speed of a light wave when it passes from one material into another.Light rays are bent as they pass from one material into another.Index of Refraction- indicates how much a material reduces the speed of light;The more light is slowed, the higher the index of refraction.
86RefractionIn prisms and rain drops, the different colors (wavelengths) are bent different amounts.Prisms separate light into visible spectrum based on wavelengths.Rainbows are cause by water droplets refracting wavelengths of sunlight.The bending separates the colors into the spectrum (red, orange, yellow, green, blue, indigo, violet)Refraction of light through air layers can produce a mirage
87Color (Page 389)When white light (mix of all colors) falls on an object, some colors are absorbed, some are reflected.We see objects in the color that is reflected by the object.The other colors are absorbed.The colors that are absorbed or reflected depend on the material.
88Light and Color (Page 389)Color is determined by the wavelength of the light the object reflects.Objects appear to be white if they reflect all colors of visible light.Objects appear to be black if they absorb, rather than reflect, all colors of light.
89Filters and PigmentsFilter- a transparent material that absorbs all colors except the color or colors it transmits.Filters can make objects appear to be different colors.A pigment is a colored material that is used to change the color of other substances.The color of the pigment is determined by the wavelength of the light reflected.
90Mixing Color (p )Mix all of the colors of light and get white light.Mix all the colors of pigments and get black since a mixture of all the colors of pigment absorb all the colors and do not reflect any, the object appears black.