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Ch. 13-16

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Wave Vibration through space and time Examples Light (electromagnetic wave): does not need a medium; vibration of electric and magnetic fields Sound: needs a medium; vibration of matter Medium: something to travel through-solid, liquid, or a gas

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Waves http://www.science-class.net/Notes/Notes_waves.htm

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definitions Crest: top of a wave Trough: bottom of wave Wavelength: distance from one crest to next Amplitude: distance of midpoint to top or bottom Cycle: mid top mid bottom midpt. Frequency: number of cycles per 1 second Frequency (Hertz) = 1/period Period: time it takes for one cycle Period(seconds) = 1/frequency

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Practice Problems 1. an electric toothbrush completes 90 cycles every second. What is the a)frequency and b) period? 2. Gusts of wind cause the Sears Building in Chicago to sway back and forth, completing a cycle every ten seconds. What at its a)frequency and b) period?

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Radio Waves Form of a wave AM stations have a frequency in kHz FM stations have a frequency in MHz When listen to 93.7 the radio is tuned to the frequency of 93,700,000 hertz (amount of times electrons in the wave vibrate per second)

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Speed of Waves Waves travel through the air or medium; medium does not move Sound wave: travels at 340 m/s = ? mph (1m =.006214 miles) What is your speed when driving a car? Can you calculate the speed of the water waves you created??

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Speed of Waves With a wave Distance between two points = wavelength Amount of time to travel = period Wave Speed = wavelength / period Period = 1 / frequency Wave speed = frequency X wavelength

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Practice Problems 1. If a train of freight cars, each 10 m long, rolls by you at the rate of three cars each second, what is the speed of the train? 2. If a water wave vibrates up and down three times each second and the distance between wave crests is 2m, what are a) the waves frequency? B) wavelength? C) wave speed?

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Types of Waves Transverse: direction wave moves is perpendicular to the vibrating source Example: strings of instruments, electromagnetic waves (radio, light, micro., x-ray) Longitudinal: direction of wave and vibrating source are parallel Example: sound

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Sound Pitch: a high frequency results in a high pitch sound seems louder (low results low pitch) Bird: high Lion: low Humans: hear 20 to 20,000 hertz frequency As age the range decreases Speakers: electrical signal vibrates the speaker, which is sent into the air to vibrate the air moleculesthis vibration causes your eardrum to vibrate and send electrical signals to the brain

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Speed of Sound in Different Mediums Dry air: 330 meters per second Warm air: sound travels faster than colder air Water: travels 4 times as fast as air Steel: travels 15 times as fast as air

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Lightening Distance away can be estimated In general sound travels 340 m/s during thunderstorms 1. What is the approximate distance of a thunderstorm (lightening) when you not a 3 second delay between the flash of lightening and the sound of thunder?

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Reflection of Sound Echo: reflection of sound Reflects off of surfaces Concert Halls: need proper balance of reflection and absorption of sound so all people can hear clearly Softer material absorbs; harder reflects Drapes, carpet Use in sonar to locate animals, submarines and planes.find earthquakes

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Refraction of Sound Bending of sound waves Remember, warmer air - sound travels faster Reflection and Refraction uses Ultrasounds X-rays Mammals: dolphinsdolphins

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Resonance Frequency of vibrations equals that of the material natural frequency Increase amplitude of the wave Tacoma Narrows Bridge

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Interference of Waves Waves can interfere with one another Same waves just produce a wave with greater amplitude Waves out of phase (opposite) cancel each other out

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Doppler Effect Change in wave frequency due to the motion of the source (or receiver) Change in volume when a noise passes Fire truck/ambulance Waves (volume increases) get closer together as come closer to object and further apart as get further away (volume decreases)

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Doppler Effect Cora.nwa.com

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In this unit: 1) Properties of light 2) Reflection 3) Colors 4) Refraction

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Vibrating electric and magnetic fields produce electromagnetic waves electromagnetic waves are a form of transverse waves Light is a form of electromagnetic wave; along with x-rays, gamma rays, radio, and micro

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Arrangement of electromagnetic waves according to their frequency (number of vibrations per second) Visible light makes up only 1 millionth of 1% em_spectrum.jpg High frequencyLow frequency

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The lowest frequency we see appears red The highest frequency we see appears violet Ultraviolet is too high of a frequency for us to see results in sun burn The frequency of the electromagnetic wave as it vibrates through space is the same as the frequency of the vibrating electric charge that generates it.

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We can only see in the visible light part of the spectrum The rest of the spectrum can not be seen with the human eye the waves are a different frequency and wavelength they all travel at the same speed High frequency short wavelength Low frequency long wavelength

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Is it correct to say that a radio wave is a low frequency light wave? Is a radio wave also a sound wave?

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Light travels in straight lines: Laser

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Light travels VERY FAST around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

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Light travels much faster than sound. For example: 1)Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

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We see things because they reflect light into our eyes: Homework

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Material that allows light to pass through in straight lines (see the same colors) Air Water Clear glass Waves (vibrations) of light can force electrons in other materials to vibrate

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Allows some light to pass through When light waves come into the material they are scattered at different angles Can not see clearly through the material Some plastics Frosted glass

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Light waves do not pass through the material The light waves are reflected or absorbed Can not see through the materials Wood Metals stone

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Shadows Shadows are places where light is blocked: Rays of light

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1) Light travels in straight lines 2) Light travels much faster than sound 3) We see things because they reflect light into our eyes 4) Shadows are formed when light is blocked by an object

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In Transparent material: Water: 75% of its speed .75 c (c=speed of light waves; 300,000 km/s) Glass: 67% .67 c Diamond: 41% .41 c

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Earths atmosphere is transparent to visible light and some infrared and ultraviolet. A very small amount of ultraviolet gets through the atmosphere Which leads to sun burns Clouds: semitransparent to ultraviolet light Results in sunburn on cloudy days

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1. Why is glass transparent to visible light, but not to ultraviolet and infrared? 2. Pretend that while you walk across a room you make several stops along the way to greet people. How is this analogous to visible light traveling through glass?

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Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

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The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

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Light is reflected due to electrons vibrating at the frequency of the electric field of light The electrons re-emit or reflect the light because of their vibrations Paper: white-emits all frequencies so you see white Ink: black-absorbs all frequencies so you see black

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Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

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1. Why is it more dangerous to drive a car on a rainy night?

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Reflect the image The image looks the same distance behind the mirror as it is in front of the mirror Due to the angle of reflection

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Flat mirrors: Produce the same image on the other side Curved mirrors: Concave: Mirror curves inward Image appears larger and further away Convex: Mirror curves outward Object appears smaller and closer

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Two examples: 1) A periscope 2) A car headlight

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Double sided Convex: rays come together at a focal point Use in glasses for far-sighted people Concave: rays are spread apart Use in glasses when near-sighted

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/ http://www.hufferamusements.com/site/pages/games-specialized.asp?ParentCategoryID=112 http://www.messersmith.name/word press/tag/funhouse-mirror/

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Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words medium, speed up, water, air, bent

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http://webecoist.com/2008/10/19/air-cloud-light-color-formations- phenomena/

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1. If the speed of light was the same in all media (plural for medium), would refraction still occur when light passes from one medium to another?

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Different light frequencies (colors) bend at different angles (refraction) in different transparent mediums rainbows

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1. If light traveled at the same speed in raindrops as it does in air, would we have rainbows?

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Bending of waves around an object or surface learn.uci.edu

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AM stations Longer wavelengths From 180 to 550 meters long Easier for longer wavelengths to bend around buildings and objects without being distorted FM stations Shorter wavelengths 2.8 to 3.4 meters Short waves dont bend well around objects

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http://planetquest.jpl.nasa.gov/technology/ diffraction.cfm

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With light Constructive Interference Results in areas of brightness Destructive Interference Results in areas of darkness ffden-2.phys.uaf.edu

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White light is not a single color; it is made up of a mixture of the seven colors of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is split up by raindrops.

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Red Orange Yellow Green Blue Indigo Violet

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White light can be split up to make separate colors. These colors can be added together again. The primary colors of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow

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The color an object appears depends on the colors of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

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A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

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If we look at a coloured object in coloured light we see something different. For example, consider a football kit: White light Shorts look blue Shirt looks red

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Filters can be used to block out different colours of light: Red Filter Magent a Filter

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In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue

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ObjectColour of light Colour object seems to be Red socks Red BlueBlack GreenBlack Blue teddy RedBlack Blue Green Green camel Red Blue Green Magenta book Red Blue Green

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Color of filterColors that could be seen Red Green Blue Cyan Magenta Yellow

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Filters are aligned Light passes through Filters are at right angles to each other Light doesnt pass through-is absorbed A third filter is placed at an angle between the two at right angles Light passes through

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Sky is blue Air mainly nitrogen and oxygen Both smaller molecules Smaller molecules scatter high frequency waves=VIOLET/BLUE

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http://www.weatherquestions.com/Why_are_sunsets_red.htm Sun has a farther distance to travel at sunrise and sunset Does a long or short wavelength diffract better? Long..=RED Red Sunsets

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Clouds are made of water droplets Droplets vary in size Different size molecules result in different frequencies of light to scatter When the different frequencies (color) combine the clouds appear white Bigger the droplets the less light gets scattered and reflected darker clouds and soon after it rains! Clouds science.nationalgeographic.com

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Know the definitions of vibration, wave, transverse, longitudinal, refraction, reflection, sonic boom, Doppler effect interference, electromagnetic wave, polarization, diffraction Examples of longitudinal and transverse waves Perform calculations using the speed of a wave equation and period Know the different parts of a wave and how changes in them affect the sound and light produced Know the difference in the speeds of waves Know how longitudinal and transverse waves travel (how different mediums/material affect their travel) Explain how mirrors work and polarized lenses Know why is the sky blue, sunsets red, clouds white.