# Waves Carry Energy, not Matter

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Waves 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.

Types of Waves All 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.

Transverse Waves A 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.

Compressional Waves Another 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.

Compressional Waves The places where the coils are squeezed together are called compressions The places where the coils are spread apart are called rarefactions. The series of compressions and rarefactions forms a compressional wave.

Waves 1 Combination Waves Seismic 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.

Electromagnetic 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.

Properties of Waves The 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.

Wavelength The 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.

Wavelength The wavelength of a compressional wave is the distance between two adjacent compressions or rarefactions.

Frequency The 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.

Period 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/sec Period (T) of a wave is the amount of time it takes one wavelength to pass a point SI Unit is sec/wavelength f= 1/T and T= 1/f

Amplitude 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.

Amplitude of a Compressional Wave
The amplitude of a compressional wave depends on the density of material in compressions and rarefactions.

Amplitude and Energy The 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.

Review- Nature of Waves
Wave- a repeating disturbance or movement that transfers energy through matter or space. Molecules pass energy on to other molecules Waves carry energy without transporting matter All waves are produced by something vibrating Medium – a material through which a wave travels Mechanical Waves Travel only through matter Transverse waves matter moves perpendicular to direction wave moves- wave in a string or slinky Compressional waves matter moves in the same direction that the wave moves.- sound waves

Review- Wave Properties
Waves differ- How much energy they carry How fast they travel How they look Transverse waves have crests and troughs Compressional waves have dense regions called compressions and less dense regions called rarefaction

Wave Properties Wave length- the distance between one point in the wave and the next corresponding part Frequency- how many waves pass a fixed point each second Expressed in hertz As frequency increases, wavelength decreases The frequency of a wave equals the rate of vibration of the source that creates it.

Wave Properties

Wave Speed The 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 Equation wave speed (m/s) = wavelength (m) X frequency (Hz) v= λf

Wave Speed In 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.

Problems P299 Example: What is the speed of a sound wave that has a wavelength of 2.00m and a frequency of Hz? V= fλ Assignment Page 299: 1-4

Amplitude 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

Amplitude 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.

Waves 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.

The Law of Reflection According 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 angle θr θi θi= θr

Refraction 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.

Refraction The 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.

Diffraction Waves 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.

Diffraction 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.

Interference Waves 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.

Interference Superposition Principle
Constructive Interference In Phase ½ λ Destructive Interference Out of Phase

Standing 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.

Resonance (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.

Waves 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.

Assignments Chapter 10 Page 299: 1-2-3-4
Chapter Review Page :9-18*, Notetaking Worksheet

Types of Waves All 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.

Amplitude 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.

Wave Speed The 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 Equation wave speed (m/s) = wavelength (m) X frequency (Hz) v= λf

Waves 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.

Making Sound Waves Vibrations 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.

Sound 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.

Sound 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.

The Speed of Sound A 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.

Problems (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?

Perception and Physical Measurement
The human ear interprets the physical characteristics of the sound waves.

The 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.

Intensity The 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.

The 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.

The 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.

Sound Intensity Decibels
Whisper 15 Normal Conversation 60 Noisy Office 80 Safe Limit 90 Ear damage Rock Concert 120 Jet engine taking off 150 TJCA Lunchroom 200

Frequency and Pitch The 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.

Ultrasonic 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.

Doppler Effect The change in pitch or wave frequency due to a moving wave source is called the Doppler Effect. See page 331

Doppler Effect Sounds moving toward a listener rise in pitch while sounds moving away from a listener lower in pitch. V=f λ λ λ f f

The 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)

Echo Distance from source
Persistence of human ear 1/10 second Speed of sound 340 m/s Distance = Wavelength of sound less than height of reflecting body Intensity of the sound sufficient to be heard after the reflection

Noise vs Music Music is pleasant to the ear Regular patterns
No sudden changes in loudness frequency wavelength

Sound Summary Sound is produced by the vibration of some object
drum head String metal tuning fork column of air Sound travels by waves but only in matter Sound waves are compressional waves Speed of Sound Sound travels only in matter Sound travels fastest in solids, slowest in gases Sound travels faster at higher temperatures

Sound Summary Amplitude of Sound Waves Frequency of Sound Waves
Amplitude is a measure of the energy of the wave Intensity is the energy divided by the area Intensity is measured in decibels The human ear can safely hear sounds with intensity between 0 db and about 120 db Loudness is how the human ear perceives intensity Frequency of Sound Waves Frequency is vibrations per second (Hz) Pitch is how the human ear perceives frequency The human ear can detect sounds between 20 Hz and 20,000 Hz

Waves in Empty Space Light 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.

Electromagnetic 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.

Producing 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 field A changing magnetic field creates an electric field.

Producing 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.

Properties 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.

EM waves are transverse waves
EM waves carry radiant energy EM waves are characterized by frequency, wavelength and velocity. V= λ f Speed of light is a constant in any medium As frequency increases, wavelength decreases Frequency is the number of vibrations per second Wavelength is the distance between crests

The Speed of Light In 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.

Wavelength 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.

Intensity 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.

The Electromagnetic Spectrum
The electromagnetic spectrum is the complete range of electromagnetic wave frequencies and wavelengths.

The Electromagnetic Spectrum
At the other end of the spectrum the waves have high frequency, short wavelength, and high energy.

The 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 Wavelength Long Wavelength Low Frequency Low Energy High Frequency High Energy

Speed, Wavelength, Frequency
Speed = frequency x wavelength V= f λ frequency increases- wavelength decreases frequency decreases- wavelength increases

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.

Infrared Waves Infrared 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.

Visible Light and Color
The range of electromagnetic waves between 700 and 400 billionths of a meter is the range of wavelengths people can see.

Ultraviolet Waves Electromagnetic 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.

X Rays and Gamma Rays The 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.

X 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.

Electromagnetic 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.

Schedule Topic Assignment Tue 2/1 Waves, Wave Measurements
Read p Worksheet Section 1&2, Wed 2/2 Wave behavior Read p , Problems P299 Thur 2/3 Wave behavior-superposition Read p Complete Note taking worksheet Fri 2/4 Chapter 10 Review Ch 10 Review Page 316:9-16, 17, 27-29 Mon 2/7 Sound waves Read p , Sound worksheet Tue 2/8 Chapter 11 Review Page 348: 8-17 Wed 2/9 Electromagnetic waves Read p , EM waves worksheets Thur 2/10 Electromagnetic Spectrum Read p Fri 2/11 Light Read p , Light worksheet Mon 2/14 Optics Lab Complete lab and all worksheets Tue 2/15 Review Mirrors and Lens NTWS Wed 2/16 Test Turn in all Homework Thur 2/17

Seeing is Reflecting Page 384
To see an object: It must produce light Or Reflect light All objects Reflect light Absorb light Some Transmit light (refract)

Matter 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.

Reflected Light Page 385 Reflection- a light wave strikes an object and bounces off. Angle of reflection = angle of incidence Regular 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.

Refracted Light Page Refraction- 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.

Refraction In 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

Color (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.

Light 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.

Filters and Pigments Filter- 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.

Mixing 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.

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