2Good vibrations All sounds are caused by something that vibrates. 1. When these vibrations collide with airmolecules (or another medium) –sound waves are formed2. Sound waves are compressional waves- they have two regions calledcompressions and rarefactions.
4Medium The type of matter that the sound waves travel through 1. A sound wave’s 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
5How Much is faster? AIR 347 m/s CORK 500 m/s WATER 1,498 m/s BRICK 3,650 m/sALUMINUM 4,877 m/s
6Turn on the Heat!3. As a medium’s temperature increases, the molecules move faster and bump into each other more often so it conducts sound faster! –
8Speed 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!
9How Loud is It? A. The amount of energy a wave carries corresponds to its amplitude, which isrelated to the density of the particles in thecompressions and rarefactions1. Intensity – The amount of energy that flows through a certain area in a specific amount of time2. Loudness – human perception of soundintensity
10IntensityIntensity of a sound describes the loudness at a particular distance from the source of the sound.
11Measure It! 3. Sound intensity is measured in decibels a) Decibels are measured in a logarithmic scale and shown by the symbol dbb) Increasing intensity by 3 db is 2 times as loud. 63 db is 2 X 60 dbc) Increasing intensity by 10 db is 10 times as loud. 70 db is 10 X 60 db
12Common Noises 1. weakest sound heard - 0 dB 2. normal conversation at 3-5 ft dB3. dial tone of telephone - 80 dB4. city traffic inside car - 85 dB5. regular sustained exposure may causepermanent damage dB6. power mower dB7. power saw dB
13Getting Really Loud 1. regular sustained exposure may cause permanent damage dB2. average Ipod on 5/10 setting - 94 dB3. bass drum rolls dB4. amplified rock music at 4-6 ft dB5. Pain begins 125 dB6. pneumatic riveter at 4 ft dB7. jet engine at 100 ft dB8. rock music peak dB9. loudest sound that can occur dB
14Pitch 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 Hz2. 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.
15Doppler Effect C. Doppler effect – Change in pitch or frequency due to a moving listener orsource
17Music Sounds that are deliberately used in a regular pattern Natural Frequency ––the frequency at which the material vibratesResonance ––The ability of a medium to vibrate by absorbing energy at its own natural frequency
18Sound QualityThe difference between sounds of the same pitch and loudness is sound qualityOvertone ––vibration with a frequency that is a multiple of the fundamental frequency
19Musical Instruments Devices used to make musical sounds Strings Sound produced by plucking, striking, or drawing a bow across tightly stressed strings bow stringsBrass and woodwinds ––air vibrations in a resonator or hollow chamber that amplifies sound – pitch determined by length of air tubePercussion ––struck shaken rubbed or brushed struck brushedBeats ––pulsing vibration in loudness pulsing loudness
21Mechanics of the ear The ear is divided into 3 parts or regions: Outer MiddleInner
22Mechanics 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.
23Mechanics 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.
27Sound Used for entertainment, warning signals, information Acoustics ––study of sound to create a good listening environmentEcholocation ––locating objects by sending out a signal and interpreting the waves reflected back
30SoundSonar ––a system that uses the reflection of underwater sounds waves to locate objects underwaterUltrasound ––used in medicine to diagnose, monitor, and treat many conditionsCan produce images of internal structuresCan treat certain medical problems such as kidney stones
32Thomas YoungIn 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.
34Light 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 mirrorRefract through a lensDiffract passing through a narrow opening
35Wave model does not explain all observations When light strikes a piece of metal, electrons get excited and may fly off the metal’s surface.Experiments show that not all colors of light can knock the electrons off the metal.Dim blue light can knock some electrons offBright red light cannot knock any electrons offHow can we explain this observation?
36Light 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 photonsPhotons are particles of lightThey do not have massThey are more like little bundles of energyUnlike energy in a wave, the energy in a photon is located in a particular place
38The 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 wavesLight exciting electrons off a metal plate are explained as particlesThe particle model can also explain how light can travel across an empty space without a mediumLight can be considered to have a “dual nature.”
39Energy 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)
40Speed of light depends on the medium In a vacuum, all light travels at the same speed “c”Speed of light is very large3 x 108 m/s (~186,000 mi/s)It is the fastest signal in the universeNothing can travel faster than the speed of light
41Speed of light depends on the medium Light also travels through transparent mediums, such as air, water, and glassWhen passing through a medium, it travels slower than it does in a vacuum.
42Brightness 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 wavesIntensity decreases as the light spreads out in spherical wave fronts.
44Sunlight 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 UVDue to the high energy, it can pass through thin layers of clouds causing you to get a sunburn on overcast days.
45X ray and gamma rays used in medicine X rays have wavelengths less than UV with higher energyGamma rays have the highest electromagnetic energy waves with the shortest wavelengthX 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 cellsGamma rays can also be used to treat cancer by killing the diseased cells.
46Infrared light can be felt as warmth Infrared (IR) light has wavelengths slightly longer than red lightIR light from the sun or heat lamp warms youUsed to keep food warm in restaurants without continuing to cook it.Devices and photographic film are sensitive to IR lightYou can detect IR radiation areas of different temperature. Therefore, mapping the area
47Microwave for cooking and communication Microwaves are centimeters longer than IR wavesMicrowave are reflected by metals but easily transmitted through air, glass, paper, and plasticMicrowaves are also used to carry telecommunication signals
49Radio waves used in communications and radar Radio waves are longer than microwavesRadio waves range from 1/10th of a meter to millions of metersThis portion includes TV signals, AM and FM radio signals, and other radio waves
51Radio waves used in communications and radar Air traffic control towers at airports use radar to determine the locations of aircraftsAntennas at the control tower emit radio waves, or sometimes microwaves, out in all directionsWhen 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.
52Radio waves used in communications and radar Radar is also used by police to monitor the speed of vehiclesThe radar gun fires a signal of known frequency at a moving vehicle then measures the frequency of the reflected wavesBecause the vehicle is moving, the reflected waves have a different frequency and use the Doppler effect to determine the speed.
54Reflection of LightA light ray is a model of light that represents light traveling through space in an imaginary straight lineIt is the same as the direction of wave travel in the wave model or the path of photons in the particle model of lightGeometrical 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
55ReflectionWhen a light wave hits an object and bounces off it is reflectedLaw of Reflection –angle of incidence = angle of reflectionRegular reflection –reflection from a smooth surfaceDiffuse reflection –reflection from a rough surface
57MirrorsFlat mirrors form virtual images from reflectionVirtual image is an image that forms at a point from which light rays appear to come but do not actually come.
58Mirrors Curved mirrors can distort images Mirrors that bulge out are called convex mirrorsIndented mirrors are called concave mirrors
59Concave mirrors create real images Concave mirrors are used to focus reflected lightIt can form one of two kinds of imagesA 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
61Determined by wavelengths of light an object reflects ColorsDetermined by wavelengths of light an object reflectsObjects appear white because they reflect all colorsObjects appear black because they absorb all colors
62Mixing colorsPigment –colored material that absorbs some colors and reflects otherPrimary colors of light –red, green, bluePrimary pigments –magenta, cyan, and yellow
63When mixing light, colors are additive –they combine to form white Mixing colorsWhen mixing light, colors are additive –they combine to form whiteWhen mixing pigment they are subtractive –they combine to form black
65Refraction of LightLight changes speed when it passes from one material to another -can cause light to bendIndex of refraction – indicates how much light slows down, the greater the index, the more light slows down –greater the index, the more the bending
67Total 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 angleReally due to refraction –light strikes a surface between two materials and is completely reflected back into the first materialUsed for fiber optics
69Lenses 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 imageConverging lens – bends light inwardDiverging lens – bends light outward
70Lenses can magnify images Magnification is a change in the size of an image compared with the size of an objectIt usually produces an image larger than the object - - but not always!
71Eye depends on refraction and lenses Light enters the eye and is focused on the retinaRetina is made of types of cells that absorb lightCones –distinguish color and detailed shapeRods –Good in dim lightColor Blindness occurs when one or more sets of cones don’t work properly
74Prisms –separate white light into visible spectrum based on λ Dispersion and PrismsPrisms –separate white light into visible spectrum based on λA prism is a transparent block with a triangular cross sectionRefraction of light through air of different densities can cause a mirage
75Dispersion and PrismsDispersion is an effect in which white light separates into its component colorsThe light separates into different colors because of differences in the wave speed
76Rainbows –caused by water droplets refracting white light They are caused by the dispersion of the sun and the reflection of water drops