CT-01: Prof. Robertson looks most like: A) Monty B) Ned C) Homer D) Chief E) Dr. HibbertBurns Flanders Simpson WigginsBACT-01: Prof. Robertson looks most like: A) Monty B) Ned C) Homer D) Chief E) Dr. HibbertBurns Flanders Simpson Wiggins3Lecture 3 – Chapter 1 •Some history of technology•How vision works•What is light•Wavelength and Frequency: c = f λScientific notation and metric unitsElectromagnetic spectrumTransmission and opacity •Speed of light •Amplitude•Direction: Rays and wavefronts•Polarization •Phase difference•Resonance•Sources of lightWe are hereReviewHow vision works:• Self luminous object: light goes to eye• Diffuse scattering at a surfaceglossy and matte surfaces • Specular reflection at a surface • Volume scattering (fog)• Transparent4ReviewLight is an electromagnetic wave• Frequency, f, measured in Hz (cycles/s)• Wavelength, λ (meters)• Scientific notation is needed because for light f is big and λ is small56Some radio wave frequencies• Submarine communication, 76 Hz• AM radio, 520 – 1610 kHz• FM radio, 87.5 – 108 MHz • GPS, 1575 MHz or 1.575 GHz• Wireless internet, 2.4 GHz• Security scanner: 1000 GHz = 1 THz The frequency of light is very high, ~1015Hz, and is off this scale.Wavelength λ of wave7λCould be measured in m, cm, mm, km, etc. λ8Wavelengths of x-rays, light, infrared, etc.nanometersHigh frequencyShort wavelengthLow frequencyLong wavelength9Visible spectrum: 400-700 nm 10How big is 500 nm? • 500 nm = 0.5 μm • Human hair is 17 – 180 μm in diameter.A 50 μm hair is 100 wavelengths. • There are 2000 wavelengths of green light per millimeter. • A “light” microscope cannot see things smaller than about 0.5 μm.11Transmission of glassOpacity is the opposite of transmission.0% transmitting is 100% opaque. Some IR is blocked.UV is blocked. No sunburn indoors. 12Opacity of atmosphereRadio communicationX ray telescope above atmosphereIR telescope above the atmosphere13For THz radiation, skin is opaque and clothing is transmitting.THz scan:14Properties of light1. Light travels in vacuum. Sound travels in air (no sound in vacuum).2. Light moves with a particular speed in vacuum, but moves less rapidly in other materials (water, glass).3. Light carries energy. (Sunlight warms, generates electricity.)4. Light travels in vacuum in straight lines (rays).Rays can be bent by materials. 5. Light has wavefronts (crests), just like water waves. If one wave is a little ahead of another, the distance one crest is in front of the other is called the phase difference.6. Light has amplitude (intensity). 7. Light has a polarization direction (or is unpolarized).15Speed of light• Measurements based on the relationdistance = velocity x time • v = distance / timeEarly observation: lightning precedes thunder. So light is faster than sound. (Sound goes 1000 ft / s, or 1 mi. in 5 s) 16Early measurements of c• 1600s: Galileo, lanterns on hilltops(“null” result)• 1800s: Roemer, light crosses earth’s orbit in 16 mins• 1800s: Fizeau, rotating gear• 1900s: Michaelson, rotating mirrorc = 300,000 km/s = 3 x 108m/s7 times around the earth in 1 s.17Fizeau’s 1849 measurement of c18The frequency-wavelength formulac = f λf = c / λλ = c / fUsing the formula:FM radio station: f = 100 MHz = 108Hzthen the wavelength is λ = [3 x 108m/s] / [108/s] = 3 mAmplitude A of a water wave19A = amplitude= half height2ATwice the amplitudeCould be measured in m, cm, mm, km, etc. 20Intensity of sunlightWe will do this better, later. Units are watts/square meter or W/m2.Watts is a unit of power. Power is energy per unit time. Sunlight delivers about 1000 Watts/m2.21Sunlight and the earth• Sunlight is constant at 1000 W/m2(UV and x-ray output varies with the 11-year sunspot cycle)• Earth’s temperature is a balance between sunlight in and infrared radiation out • Carbon dioxide blocks infrared going out and has a warming effect. 22Lecture 3 – Chapter 1 We are here•Some history of technology•How vision works•What is light•Wavelength and Frequency: c = f λScientific notation and metric unitsElectromagnetic spectrumTransmission and opacity •Speed of light •Amplitude•Direction: Rays and wavefronts•Polarization •Phase difference•Resonance•Sources of lightWavefronts23Wave crests or wavefrontsWave troughRays are perpendicular to fronts24RaysWave crests or wavefrontshttp://en.wikipedia.org/wiki/Wavefrontshttp://en.wikipedia.org/wiki/File:Two_sources_interference.gifRight
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