Presentation on theme: "12345671234567 Waves carry energy from one place to another. Transverse and longitudinal waves exist in mechanical media, such as springs and ropes, and."— Presentation transcript:
Waves carry energy from one place to another. Transverse and longitudinal waves exist in mechanical media, such as springs and ropes, and in the Earth as seismic waves. Wavelength, frequency and wave speed are related. Sound is a longitudinal wave whose speed depends on the properties of the medium in which it propagates. Radio waves, light and X-rays are different wavelength bands in the spectrum of electromagnetic waves, the speed of which in a vacuum is approximately 3 x 10 8 m/s, and less when passing through other media. Waves have characteristic behaviors, such as interference, diffraction, refraction and polarization. Beats and the Doppler Effect result from the characteristic behavior of waves. Waves have characteristic properties that do not depend on the type of wave.
What are they? Are these the same things? Radio Waves Microwaves Infrared Visible Light Ultraviolet Light X-rays Gamma Rays Before we answer that question, lets review some metric units & scientific notation.
PrefixSymbolValueDescription picop picometer, (pm) = m nanon nanometer, (nm) = m microµ or u micrometer (µm) = m millim millimeter (mm) = m centic centimeter (cm) = 0.01 m decid decimeter (dm) = 0.1 m NONE 1normal units without prefixes kilok kilohertz (kHz) = 1000 Hz megaM megahertz (MHz) = 1,000,000 Hz gigaG gigahertz (GHz) = 1,000,000,000 Hz teraT terahertz (THz) = 1,000,000,000,000 Hz
Are all parts of the electromagnetic spectrum and are fundamentally the same thing. They are all electromagnetic radiation. The electromagnetic spectrum can be expressed in terms of wavelength, frequency, or energy. Radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
v = f x λ v = f x λ v = f x λ 300,000,000 m/s = speed of light 340 m/s = speed of sound 3*10 8 m/s = 3*10 5 Hz x 1*10 3 m
Speed of light in a vacuum 299,792,458 m/s (1,079,252,849 km/h)299,792,458 c = 3×10 8 m/s c = 3×10 8 m/s (Approximate Value) v = f x λ 300,000,000 m/s = speed of light 340 m/s = speed of sound
Energy E = h x f h = × joule·seconds h = x eV·seconds (Planks Constant) h = × joule·seconds h = x eV·seconds Higher Energy Lower Energy 1 eV = ×10 19 J ×10 19J
E = h x f h = × J·sec h = × J·sec (Planks Constant) EM WaveFreq (Hz) h x f = EEnergy Television10 8 Hz(6.626 x ) x (10 8 )6.6 x J Infrared10 14 Hz(6.626 x ) x (10 14 )6.6 x J Ultra Violet10 16 Hz(6.626 x ) x (10 16 )6.6 x J X-Rays10 18 Hz(6.626 x ) x (10 18 )6.6 x J Energy in Electro Magnetic Waves What about a Microwave at 3,000 MHz (3.0 x 109 Hz)?
NOTE: a 1KW microwave oven with a frequency of 2999 MHz produces 5.0 x photons per second. If a single microwave (photon) has a frequency of 3,000 MHz, how much energy will it have? E = h x f h = × J·sec E = (6.626 × J·sec) x (3.0 x 10 9 Hz) E = 1.99 x J per photon E = (1.99 x J) x (5.0 x ) = 994,000 J per second KE = ½ mv 2 994,000 J = ½ * 1179 Kg * 41 m/s 994,000 J = ½ * Toyota * 90 mph EM(Hz)Energy TV10 8 Hz6.6 x J IR10 14 Hz6.6 x J UV10 16 Hz6.6 x J X-Rays Hz6.6 x J Note: most microwaves operate at 2,450 MHz not 2,999 MHz
The above image shows the Carbon Monoxide (CO) gases in our Milky Way galaxy. Cellular Radio Waves - Longest wavelengths in the EM spectrum Radio waves can penetrate the earths atmosphere – radio astronomy Waves can be longer than a ten football fields or as short as a football. 100 kHz 1 GHz
Radio Waves - Common frequency bands include the following: - AM radio kilohertz to 1.7 megahertz -Short wave radio - bands from 5.9 megahertz to 26.1 megahertz -Citizens band (CB) radio megahertz to megahertz - Television stations - 54 to 88 megahertz for channels 2 through 6 - FM radio - 88 megahertz to 108 megahertz -Television stations to 220 megahertz for channels 7 through 13 Every wireless technology you can imagine has its own little band: -Garage door openers, alarm systems, etc. - Around 40 megahertzalarm systems -Standard cordless phones: Bands from 40 to 50 megahertzcordless phones -Baby monitors: 49 megahertz -Radio controlled airplanes: Around 72 megahertz, which is different from...Radio controlled airplanes -Radio controlled cars: Around 75 megahertzRadio controlled cars -Wildlife tracking collars: 215 to 220 megahertz -MIR space station: 145 megahertz and 437 megahertzspace station - Cell phones : 824 to 849 megahertz -New 900-MHz cordless phones: Obviously around 900 megahertz! -Air traffic control radar: 960 to 1,215 megahertzAir traffic control -Global Positioning System: 1,227 and 1,575 megahertzGlobal Positioning System -Deep space radio communications: 2290 megahertz to 2300 megahertz
Radio Waves - Longest wavelengths in the EM spectrum
Centimeters 100 kHz 1 GHz Microwave Ovens radar Shorter microwaves are used in remote sensing. These microwaves are used for radar like the doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long transmitting information Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. (point - to - point) Radar is an acronym for "radio detection and ranging"
Special cameras and film that can detect differences in temperature, and then assign different brightnesses or false colors to them. 750 nm 1 x10 12 Hz 4 x10 14 Hz thermal form of heat ! Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat ! The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared TV's remote control. Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control.
Which EM wavelengths can make it through our Atmosphere? H e a t
or escape Visible light can easily penetrate the atmosphere, Infrared can not penetrate (or escape) as easily.
(approximately 400 – 700 nm) Though electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to only a very narrow band – visible light. (approximately 400 – 700 nm) ColorWavelength violet380–450 nm blue450–495 nm green495–570 nm yellow570–590 nm orange590–620 nm red620–750 nm
Though these waves are invisible to the human eye, some insects, like bumblebees, can see them! 400 nm 10 nm 1 x10 15 Hz 3 x10 16 Hz UVB 297 nm Health concerns for UV exposure are mostly for the range nm in wavelength, the range called UVB. The most effective biological wavelength for producing skin burns is 297 nm UVA 400 nm – 315 nm(Black Lights) UVB 315 nm – 280 nm(Sun Burn) UVC 280 nm – 100 nm(germicidal) A sterilization method that uses ultraviolet (UV) light to break down micro-organisms. (Food, air and water purification.)sterilization ultraviolet micro-organisms
Because your bones and teeth are dense and absorb more X-rays then your skin does, silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent. Metal absorbs even more X-rays. Many things in space emit X-rays, among them are black holes, neutron stars, binary star systems, supernova remnants, stars, the Sun, and even some comets! We usually talk about X-rays in terms of their energy rather than wavelength. 1 x10 16 Hz 1 x10 18 Hz
Many things in deep space give off X-rays. Many stars are in binary star systems - which means that two stars orbit each other. When one of these stars is a black hole or a neutron star, material is pulled off the normal star. This materials spirals into the black hole or neutron star and heats up to very high temperatures. When something is heated to over a million degrees, it will give off X-rays! The above image is an artist's conception of a binary star system - it shows the material being pulled off the red star by its invisible black hole companion and into an orbiting disk.
1 x10 18 Hz Smallest wavelengths and the most energy of any other wave in the Electromagnetic spectrum. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells. These waves are generated by radioactive atoms and in nuclear explosions.
more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! Gamma-ray bursts can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! So far, it appears that all of the bursts we have observed have come from outside the Milky Way Galaxy. The sources of these enigmatic high-energy flashes remain a mystery. Gamma Rays – ENERGITICALLY Interesting Facts By solving the mystery of gamma-ray bursts, scientists hope to gain further knowledge of the origins of the Universe, the rate at which the Universe is expanding, and the size of the Universe. Smallest wavelengths Highest frequency Most energy E = h x f v = f x λ
What is the only thing that we (humans) can see? A very small band of the electromagnetic spectrum between 380 – 750 nm (400 – 700 nm) LIGHT LIGHT LIGHT
Sight & Light Rods & Cones send signals to the brain What is occurring between our eyes and the objects that we see? Is there anything traveling between our eyes and the objects?
What do you see? WAIT - Dont say it out loud. An electromagnetic wave with a wavelength of approx. 600 nm
White Light All visible wavelengths Energy traveling as EM waves through a medium (or a vacuum) Until the EM waves hit an object What do the EM waves do when they hit an object?
Reflected light Daylight - Not a perfect spectrum We see the wavelengths of light that are reflected off of the object. All other wavelengths are absorbed by the object. The wavelengths of light we see
Color absorption by different glass Do we see all of wavelengths of visible light at the same intensity?
Daylight bulb Incandescent bulb Mercury Lamp Sodium Lamp (low pressure) Sodium Lamp (high pressure) Did the actual paint on the walls change?
Spectral lines Neon Spectrum What is the perceived color of the light source? Perceived color VS actual wavelengths present in the light source. Not every wavelength present What are the wavelengths of these spectral lines?
||||||||||||||||||||||||||||||||||||||||| | 7 | 6 | 5 | 4 | | | | | | | | | | Todays Lab Determine the wavelengths that are present in six different light sources ||||||||||||||||||||||||||||||||||||||||| | 7 | 6 | 5 | 4 | | | | | | | | | | Lab Report Dark Red Yellow/Orange Blue
Visible Light & Wavelength Let us return to the lab we did last class Wave speed did not change
R + B B + G RGB R + G Simulation – mixing colors of light (over lapping) Green – Magenta Red – Cyan Blue – Yellow Colors of Light
||||||||||||||||||||||||||||||||||||||||| | 7 | 6 | 5 | 4 | | | | | | | | | | Helium Spectral Lines – Lab Results ||||||||||||||||||||||||||||||||||||||||| | 7 | 6 | 5 | 4 | | | | | | | | | | Perceived color = pink? Note that the intensity (the brightness) of each band is different
Fluorescent Tube Spectral Lines - Results Hallway Fluorescent lights Note the differences in intensity
400 nm 700 nm Natural Light (sun light on sky bridge) Incandescent Bulb (night light) older type Fluorescent Bulb - older type - (single tube) Newer type Fluorescent Bulb - Newer type - (hallway lights) Energy Saver Fluorescent Bulb - Energy Saver - (not in class)
Bohr model of an atom Excited Ground Electron Excitation and Emission (at a lower energy)
Photon Absorption & Emission for a hydrogen atom Spectral Lines Creating an Emission Line (Spectral Lines) Hydrogen HeliumNeon
Spectral Lines of various elements
Color Wavelength (nm) h x f = E Violet (6.626 x ) x (1.36 x Hz) Violet (6.626 x ) x (1.45 x Hz) Bluegreen (cyan) (6.626 x ) x (1.62 x Hz) Red (6.626 x ) x (2.19 x Hz) Red (6.626 x ) x (2.19 x Hz) 400 nm 500 nm 600 nm 700 nm E = h x f h = × J·sec h = × J·sec (Planks Constant)
Simulation – mixing colors of light (what people see) Excited Ground Green & Yellow are the only wavelengths that are reflected.
Filters (Only Specific Wavelengths)
Every substance is uniqueExcited Ground
Slowing down and changing the direction of light Degree of Scattering
Degree of Scattering Selective Scattering
Why… Is the sky blue? Are clouds white/gray? Is the ocean blue/green? Are sunsets red/golden? I need some new/better PPT slides to explain why…
Designing new PowerPoint Slides HOMEWORK: Designing new PowerPoint Slides Chose One: blue-sky, white clouds, blue/green oceans, red sunsets Include: 1- How sunlight is a combination of all wavelengths (colors) of light 2- Which EM wavelengths/frequencies are involved (how) 3- How light is absorbed, reflected, scattered, etc. 4- What is occurring at the atomic level (Absorption & Emission) Chapters 27 & 28 – Sections 27.4, 27.5, 28.3, 28.7 – On the computer OR hand drawn
Electric charges vibrate in a variety of directions, thus creating an electromagnetic wave which vibrates in a variety of directions. Unpolarized Light - waves vibrating in more than one plane Polarized light - waves vibrating in a single plane. Unpolarized Unpolarized Unpolarized Polarized
Polarization – process of transforming unpolarized light into polarized light. (Filter)
Using two polarization filters Polarization axis aligned Polarization axis perpendicular Two Polarization filter - simulation
Polarization by reflection Glare from the Road Removing the Glare
Question Consider the three pairs of sunglasses below. Identify the pair of glasses is capable of eliminating the glare resulting from sunlight reflecting off the calm waters of a lake? _________ (The polarization axes are shown by the straight lines.) 3-D Glasses
Incident Ray Incident Ray - the ray of light approaching the mirror Reflected Ray - the ray of light which leaves the mirror The Normal - an imaginary line perpendicular to mirror Angle of Incidence Angle of Incidence - the angle between the incident ray and the normal Angle of Reflection - the angle between the reflected ray and the normal The law of reflection - when a ray of light reflects off a surface the angle of incidence is equal to the angle of reflection N
Question -1. Consider the diagram above. Which one of the angles (A, B, C, or D) is the angle of incidence? ______ -2. Which one of the angles is the angle of reflection? ______
Question A ray of light is incident towards a plane mirror at an angle of 30-degrees with the mirror surface. What will be the angle of reflection?
Reflection off of different types of surfaces Specular reflection - Reflection off of smooth surfaces such as mirrors or a calm body of water Diffuse reflection - Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway Scatters Light in all directions
Rough Surface: Wet vs Dry
The law of reflection - the angle of incidence is equal to the angle of reflection (when a ray of light reflects off a surface ). Reflection off different types of surfaces What if the Blue floor had a rougher texture?
17 meter Since sound waves travel at about 340 m/s at room temperature, it will take approximately 0.1 s for a sound to travel the length of a 17 meter room and back, thus causing a reverberation 0.1 seconds Echoes - when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard. 0.1 seconds Reverberations - the prolonging of a sound. The reception of multiple reflections off of walls and ceilings within (less than) 0.1 seconds of each other Reflection of waves --- More than just light > 17 m
Reflection of waves --- More than just lightRadar
Rough walls tend to diffuse sound, reflecting it in a variety of directions. This allows a spectator to perceive sounds from every part of the room, making it seem lively and full. Smooth walls direct sound waves in a specific direction. Reflection of waves --- More than just light Focusing waves
Boundary - When one medium ends, another medium begins; and the behavior of a wave at that boundary is described as its boundary behavior. Change of medium at the boundary Slows Down Speeds Up The speed of a wave is determined by the medium
The boundary behavior of waves - summarized 1- the wave speed is always greatest in the least dense medium 2- the wavelength is always greatest in the least dense medium 3- the frequency of a wave is not altered by crossing a boundary Faster Slower Faster Slower Greater λ Smaller λ Frequency does not change
Question A pulse in a more dense medium is traveling towards the boundary with a less dense medium. (greater than, less than, the same as) 1.The speed of the pulse in the less dense medium will be _______ (greater than, less than, the same as) the speed of the incident pulse coming from the more dense medium. (greater than, less than, the same as) 2. The wavelength of the pulse in the less dense medium will be _______ (greater than, less than, the same as) the wavelength of the incident pulse coming from the more dense medium. (greater than, less than, the same as) 3. The frequency of the pulse in the less dense medium will be _______ (greater than, less than, the same as) the frequency of the incident pulse coming from the more dense medium.
Does the straw break? Refraction
Minuscule amount of time before release Speed of Light Minuscule amount of time before release Speed of Light Start FinishPhoton Photon Photon Dense Denser Densest Higher Density = Slower wave speed
Refraction – Tractor Model
Reflection - change in direction of waves when they bounce off a barrier. Refraction change in the direction (bending) of waves as they cross from one medium to another. -Caused by a change in speed and wavelength of the waves Refraction – wave fronts Refraction (bending) only occurs at the boundary. Air Less Dense Faster Glass More Dense Slower
The boundary behavior of waves - summarized 1- the wave speed is always greatest in the least dense medium 2- the wavelength is always greatest in the least dense medium 3- the frequency of a wave is not altered by crossing a boundaryFaster Slower Faster Slower Greater λ Smaller λ Frequency does not change Refraction Index simulator - including refraction of individual wavelengths More Dense = greater angle
materialn n Vacuum1Crown Glass1.52 Air1.0003Salt1.54 Water1.33Asphalt1.635 Ethyl Alcohol1.36Heavy Flint Glass1.65 Fused Quartz1.4585Diamond2.42 Whale Oil1.460Lead2.6 The amount by which light slows (and therefore bends) in a given material is described by the index of refraction n = c/v Dense Slow Denser Slower Densest Slowest Refraction Index, Total Internal Reflection, and Critical Angle Simulation More dense More bending
Total Internal Reflection (TIR) - when the angle of incidence is greater than the critical angle, no refraction occurs. --Depends upon the Angle of Incidence & the medium density The Sparkle of Diamonds – All incoming light can only exit the diamond out of the top of the gem Refractive Index Critical Angle
Reflection at the Critical Angle (Total Internal Reflection) Critical Angle of Reflection Simulation Critical Angle - The largest angle of incidence for which refraction can still occur. The angle of incidence yields an angle of refraction of 90-degrees. For any angle of incidence greater than the critical angle, light will undergo total internal reflection (TIR). Refraction Critical Angle Total Internal Reflection
Dispersion - the separation of visible light into its different colors Refraction simulator including individual wave lengths Drop of water
How are rainbows formed? Prism
Rainbows – Refraction, Dispersion, Reflection Bending of light Color Separation Direction Change all wavelengths -Incident white light contains all wavelengths reflected -Some of the light is reflected refracted -The rest of the light is refracted (dispersion) -Light splits (dispersion) into component colors Reflected -Reflected at rear of raindrop (TIR – Total internal Reflection) Refracted -Refracted again as it leaves raindrop dispersed -Colors are further dispersed White light Air H2OH2OH2OH2O
4042 Rainbows – Dependant on the angles ( °)
Greater angle of incidence = greater angle of refraction
Diffraction - a change in direction of waves as they pass through an opening or around an obstacle in their path. (not across a boundary/medium change) Refraction Diffraction Boundary Opening
bounce off a barrier Reflection - change in direction of waves when they bounce off a barrier. (Also total interior reflection - TIR) one medium to another. Refraction - change in the direction of waves as they pass from one medium to another. pass through an openingaround an obstacle Diffraction - change in direction of waves as they pass through an opening or around an obstacle in their path. Interference
Constructive & Destructive Wave Interference
Constructive interference occurs wherever a thick line meets a thick line or a thin line meets a thin line; this type of interference results in the formation of an antinode. Destructive interference occurs wherever a thick line meets a thin line; this type of interference results in the formation of a node.. `