Sound and Light

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Sound and Light

• Unit 9
• Chapter 12

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Good vibrations

• All sounds are caused by something
• that vibrates.
• 1. When these vibrations collide with air
• molecules (or another medium)
• sound waves are formed
• 2. Sound waves are compressional waves
• - they have two regions called
• compressions and rarefactions.

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Compressional Waves

• Rarefaction air molecules pulled apart
• Compression air molecules pushed together
  

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Medium

• The type of matter that the sound waves travel
  through
• 1. A sound waves speed depends on the substance
  solid liquid or gas.
• Sound need a medium it cannot travel in a
  vacuum!
• 2. Sound travels more quickly through solids and
  liquids because their particles are closer
  together than in a gas

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How Much is faster?

• AIR 347 m/s
• CORK 500 m/s
• WATER 1,498 m/s
• BRICK 3,650 m/s
• ALUMINUM 4,877 m/s

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Turn on the Heat!

• 3. As a mediums temperature increases, the
  molecules move faster and bump into each other
  more often so it conducts sound faster!

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Properties of Sounds
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Speed of sound

• The speed of sound depends on the medium.
• Sound waves travel faster through liquids and
  solids than through gases.
• The particles are much closer in liquids and
  solids so the vibrations are transferred much
  faster from one particle to the next.
• EXCEPTS Solids such as rubber dampen vibrations
  so that sound travels very slowly. Materials
  like this can be used for soundproofing!

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How Loud is It?

• A. 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
• 1. Intensity The amount of energy that flows
  through a certain area in a specific amount of
  time
• 2. Loudness human perception of sound
• intensity

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Intensity

• Intensity of a sound describes the loudness at a
  particular distance from the source of the sound.

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Measure It!

• 3. Sound intensity is measured in decibels
• a) Decibels are measured in a logarithmic scale
  and shown by the symbol db
• b) Increasing intensity by 3 db is 2 times as
  loud. 63 db is 2 X 60 db
• c) Increasing intensity by 10 db is 10 times as
  loud. 70 db is 10 X 60 db

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Common Noises

• 1. weakest sound heard - 0 dB
• 2. normal conversation at 3-5 ft - 60-70 dB
• 3. dial tone of telephone - 80 dB
• 4. city traffic inside car - 85 dB
• 5. regular sustained exposure may cause
• permanent damage - 90-95 dB
• 6. power mower - 107 dB
• 7. power saw - 110 dB

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Getting Really Loud

• 1. regular sustained exposure may cause
• permanent damage - 90-95 dB
• 2. average Ipod on 5/10 setting - 94 dB
• 3. bass drum rolls - 106 dB
• 4. amplified rock music at 4-6 ft. - 120 dB
• 5. Pain begins 125 dB
• 6. pneumatic riveter at 4 ft. - 125 dB
• 7. jet engine at 100 ft. - 140 dB
• 8. rock music peak - 150 dB
• 9. loudest sound that can occur - 194 dB

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Pitch

• B. Pitch how low or high a sound seems to be
• 1. Frequency is the number of compressions or
  rarefactions of a sound wave that pass per second
  humans hear about 20 20,000 Hz
• 2. Ultrasonic over 20,000. Is outside the
  range of human hearing.
• 3. Infrasonic or subsonic below 20 Hz may be
  felt like a rumble but not heard. It is any
  frequency above human hearing range.

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Doppler Effect

• C. Doppler effect Change in pitch or
• frequency due to a moving listener or
• source

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Music
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Music

• Sounds that are deliberately used in a regular
  pattern
• Natural Frequency the frequency at which the
  material vibrates
• Resonance The ability of a medium to vibrate
  by absorbing energy at its own natural frequency

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Sound Quality

• The difference between sounds of the same pitch
  and loudness is sound quality
• Overtone vibration with a frequency that is a
  multiple of the fundamental frequency

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Musical Instruments

• Devices used to make musical sounds
• Strings
• Sound produced by plucking, striking, or drawing
  a bow across tightly stressed strings bow strings
• Brass and woodwinds air vibrations in a
  resonator or hollow chamber that amplifies sound
  pitch determined by length of air tube
• Percussion struck shaken rubbed or brushed
  struck brushed
• Beats pulsing vibration in loudness pulsing
  loudness

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Hearing and the Ear
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Mechanics of the ear

• The ear is divided into 3 parts or regions
• Outer
• Middle
• Inner

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Mechanics of the ear cont.

• Sound enters through the outer ear and down the
  ear canal. The ear canal ends with the eardrum
  (thin flat piece of tissue).
• When sound hits the eardrum, it vibrates.
• These vibrations pass through the small bones of
  the middle ear (Hammer, anvil, and stirrup)
• When vibrations reach the stirrup, the stirrup
  strikes a membrane at the opening of the inner
  ear.

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Mechanics of the ear cont.

• The waves in the inner ear go through the
  spiral-shaped cochlea (also called the basilar
  membrane).
• Different parts of the basilar membrane vibrate
  at different natural frequencies.
• As the waves pass through the cochlea, they
  resonate with specific parts of the basilar
  membrane.
• Hairs near this area stimulate nerve fibers which
  send an impulse to the brain.
• The brain interprets this impulse as a sound with
  a specific frequency.

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Using Sound
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Sound

• Used for entertainment, warning signals,
  information
• Acoustics study of sound to create a good
  listening environment
• Echolocation locating objects by sending out a
  signal and interpreting the waves reflected back

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Sound

• Sonar a system that uses the reflection of
  underwater sounds waves to locate objects
  underwater
• Ultrasound used in medicine to diagnose,
  monitor, and treat many conditions
• Can produce images of internal structures
• Can treat certain medical problems such as kidney
  stones

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The Nature of Light
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Thomas Young

• In 1801, Thomas Young devised an experiment to
  test the nature of light. He realized that the
  pattern created is similar to the pattern caused
  by water waves interfering such as the ripple
  tank.

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Light can be modeled as a wave

• We have learned light waves can be described as
  transverse wave which do not require a medium.
• They are also called electromagnetic waves
  because they consist of changing electric and
  magnetic fields.
• Light waves can
• Reflect in a mirror
• Refract through a lens
• Diffract passing through a narrow opening

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Wave model does not explain all observations

• When light strikes a piece of metal, electrons
  get excited and may fly off the metals surface.
• Experiments show that not all colors of light can
  knock the electrons off the metal.
• Dim blue light can knock some electrons off
• Bright red light cannot knock any electrons off
• How can we explain this observation?

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Light can modeled as a stream of particles

• One explanation to the effects of light striking
  a metal plate is so assume that the energy of
  light is contained in small packets.
• These packets are called photons
• Photons are particles of light
• They do not have mass
• They are more like little bundles of energy
• Unlike energy in a wave, the energy in a photon
  is located in a particular place

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The light model used depends on the situation

• Light can be modeled as either waves or
  particles.
• Some effects such as
• Interference of light are explained as waves
• Light exciting electrons off a metal plate are
  explained as particles
• The particle model can also explain how light can
  travel across an empty space without a medium
• Light can be considered to have a dual nature.

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Energy of light is proportional to frequency

• Remember light is a form of energy!
• Each photon of light carries a small amount of
  energy.
• The amount of this energy is proportional to the
  frequency of the corresponding wavelength.
• Photon of red light carries an amount of energy
  that corresponds to the frequency of waves in red
  light (4.5 x 1014 Hz)

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Speed of light depends on the medium

• In a vacuum, all light travels at the same speed
  c
• Speed of light is very large
• 3 x 108 m/s (186,000 mi/s)
• It is the fastest signal in the universe
• Nothing can travel faster than the speed of light

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Speed of light depends on the medium

• Light also travels through transparent mediums,
  such as air, water, and glass
• When passing through a medium, it travels slower
  than it does in a vacuum.

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Brightness of light depends on intensity

• Intensity is the rate at which light or any other
  form of energy flows through a given area of
  space.
• It depends on the amount of light or the number
  of photons or waves
• Intensity decreases as the light spreads out in
  spherical wave fronts.

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Electromagnetic Spectrum

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Sunlight contains UV light

• The invisible light just beyond violet light
  falls into the UV portion of the spectrum.
• It has higher energy and shorter wavelengths than
  visible light.
• 9 of energy emitted by the sun is UV
• Due to the high energy, it can pass through thin
  layers of clouds causing you to get a sunburn on
  overcast days.

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X ray and gamma rays used in medicine

• X rays have wavelengths less than UV with higher
  energy
• Gamma rays have the highest electromagnetic
  energy waves with the shortest wavelength
• X rays are helpful in diagnostic in medicine but
  can be dangerous to the body.
• Both of these waves can kill living cells or turn
  them into cancerous cells
• Gamma rays can also be used to treat cancer by
  killing the diseased cells.

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Infrared light can be felt as warmth

• Infrared (IR) light has wavelengths slightly
  longer than red light
• IR light from the sun or heat lamp warms you
• Used to keep food warm in restaurants without
  continuing to cook it.
• Devices and photographic film are sensitive to IR
  light
• You can detect IR radiation areas of different
  temperature. Therefore, mapping the area

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Microwave for cooking and communication

• Microwaves are centimeters longer than IR waves
• Microwave are reflected by metals but easily
  transmitted through air, glass, paper, and
  plastic
• Microwaves are also used to carry
  telecommunication signals

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Radio waves used in communications and radar

• Radio waves are longer than microwaves
• Radio waves range from 1/10th of a meter to
  millions of meters
• This portion includes TV signals, AM and FM radio
  signals, and other radio waves

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Radio waves used in communications and radar

• Air traffic control towers at airports use radar
  to determine the locations of aircrafts
• Antennas at the control tower emit radio waves,
  or sometimes microwaves, out in all directions
• When the signal reaches an airplane, a
  transmitter on the plane sends another radio
  signal back to the control tower indicating the
  planes location and elevation above the ground.

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Radio waves used in communications and radar

• Radar is also used by police to monitor the speed
  of vehicles
• The radar gun fires a signal of known frequency
  at a moving vehicle then measures the frequency
  of the reflected waves
• Because the vehicle is moving, the reflected
  waves have a different frequency and use the
  Doppler effect to determine the speed.

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Reflection and Color
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Reflection of Light

• A light ray is a model of light that represents
  light traveling through space in an imaginary
  straight line
• It is the same as the direction of wave travel in
  the wave model or the path of photons in the
  particle model of light
• Geometrical optics is the study of light in
  circumstances where it behaves like a ray.
• Using the light rays, the path of light can be
  traced in ray diagrams

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Reflection

• When a light wave hits an object and bounces off
  it is reflected
• Law of Reflection angle of incidence angle of
  reflection
• Regular reflection reflection from a smooth
  surface
• Diffuse reflection reflection from a rough
  surface

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Law of reflection
normal
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Mirrors

• Flat mirrors form virtual images from reflection
• Virtual image is an image that forms at a point
  from which light rays appear to come but do not
  actually come.

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Mirrors

• Curved mirrors can distort images
• Mirrors that bulge out are called convex mirrors
• Indented mirrors are called concave mirrors

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Concave mirrors create real images

• Concave mirrors are used to focus reflected light
• It can form one of two kinds of images
• A virtual image behind the mirror or a real image
  in front of the mirror.
• Real image is an image of an object formed by
  many light rays coming together in a specific
  location

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Telescope use curved surfaces to focus light
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Colors

• Determined by wavelengths of light an object
  reflects
• Objects appear white because they reflect all
  colors
• Objects appear black because they absorb all
  colors

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Mixing colors

• Pigment colored material that absorbs some
  colors and reflects other
• Primary colors of light red, green, blue
• Primary pigments magenta, cyan, and yellow

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Mixing colors

• When mixing light, colors are additive they
  combine to form white
• When mixing pigment they are subtractive they
  combine to form black

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Refraction, Lenses, and Prisms
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Refraction of Light

• Light changes speed when it passes from one
  material to another -can cause light to bend
• Index of refraction indicates how much light
  slows down, the greater the index, the more light
  slows down greater the index, the more the
  bending

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Total Internal Reflection

• Total internal reflection is the complete
  reflection of light at the boundary between two
  transparent mediums when the angle of incidence
  exceeds the critical angle
• Really due to refraction light strikes a surface
  between two materials and is completely reflected
  back into the first material
• Used for fiber optics

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Fiber Optics
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Lenses

• Lenses rely on refraction
• Light traveling at an angle through a flat piece
  of glass is refracted twice once when it enters
  the glass and again when it reenters the air.
• Lens are a transparent object that refracts light
  rays, causing them to converge or diverge to
  create an image
• Converging lens bends light inward
• Diverging lens bends light outward

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Lenses can magnify images

• Magnification is a change in the size of an image
  compared with the size of an object
• It usually produces an image larger than the
  object - - but not always!

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Eye depends on refraction and lenses

• Light enters the eye and is focused on the retina
• Retina is made of types of cells that absorb
  light
• Cones distinguish color and detailed shape
• Rods Good in dim light
• Color Blindness occurs when one or more sets of
  cones dont work properly

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Dispersion and Prisms

• Prisms separate white light into visible
  spectrum based on ?
• A prism is a transparent block with a triangular
  cross section
• Refraction of light through air of different
  densities can cause a mirage

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Dispersion and Prisms

• Dispersion is an effect in which white light
  separates into its component colors
• The light separates into different colors because
  of differences in the wave speed

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Rainbows

• Rainbows caused by water droplets refracting
  white light
• They are caused by the dispersion of the sun and
  the reflection of water drops

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