11Lecture 4 – 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 hereWe got to slide 24 on Thursday. Amplitude A of a water wave2A = amplitude= half height2ATwice the amplitude as the wave aboveCould be measured in m, cm, mm, km, etc.Wavefronts3Wave crests or wavefrontsWave troughRays are perpendicular to fronts4RaysWave crests or wavefrontshttp://en.wikipedia.org/wiki/Wavefrontshttp://en.wikipedia.org/wiki/File:Two_sources_interference.gifRight click5Polarization5Vertical polarization has electric field “up and down”Horizontal polarization has electric field “left and right”Demo polarizing sheets, grill6Polarizing filter6Ordinary light has both polarizations.Polarizing filters pass only one polarization.We return to this in Chapter 13.Review• Wavelength λ is distance from crest to crest• Frequency f is the number of full cycles per second• c = 300,000 km/s =3 x 108m/s•c = fλ, units are Hz for f and meters for λ• wavelength of light spans 400 nm – 700 nm(blue to red) • Atmosphere transmits light and radio, is opaque to most UV, x-rays, some IR• Amplitude of a water wave is the half-height78Review9In phase or out of phase?9In-phase wavesCombined waves are biggerOut-of-phase wavesCombined wave is smaller in amplitude!10Waves can go in and out of phaseif their frequency is different!In-phase Out of phase(add) (subtract)Demo: vibraphone bars (also see web link on previous slide)Time or distance Demohttp://paws.kettering.edu/~drussell/Demos/superposition/superposition.html11Phase difference11Phase differenceWe will discuss the units later. 12ResonanceThings that oscillate have a natural frequency:the resonant frequency.• Pendulum• Guitar or piano string• Quartz crystal (in a watch)• Electrical circuits (transmitters & receivers)• TV phosphors emit red, green, blue• Nerve cells sensitive to red, green, blue• Molecules in paints and dyes13Resonant excitationA “pushed” oscillator responds more at its resonant frequency. We see blue when nerve cells resonant at the bluefrequency are excited.Demo: vibraphone bars again, pushed leaf springCT-01: Prof. Robertson looks most like: A) Monty B) Ned C) Homer D) Chief E) Dr. HibbertBurns Flanders Simpson WigginsDCTo change your iClicker frequency, turn on your iClicker. Hold down on the power button until the power light blinks. Then hit DC. You should see a green light indicating that you have changed the frequency.CT-01: Prof. Robertson looks most like: A) Monty B) Ned C) Homer D) Chief E) Dr. HibbertBurns Flanders Simpson WigginsConcept questionWhat is the wavelength of red light?A. 6500 nmB. 0.650 μmC. 650 μm D. 65 nmE. 65 mm16Concept questionWhat is the wavelength of red light?A. 6500 nmB. 0.650 μmC. 650 μm D. 65 nmE. 65 mm1718Concept question• The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one cma) 20 thousandb) 50 thousandc) Two milliond) Two billione) 5 billion• wavelength = 500 nm = 5 x 102x10-9 m = 5 x 10-7 m• Distance = 1 cm =10-2m• Hence number = distance/wavelength = 10-2m /(5 x 10-7 m) = 105/5 = 104/ 0.510,000 x 2 = 20,000 wavelengths in a cm19Concept question• The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one cma) 20 thousandb) 50 thousandc) Two milliond) Two billione) 5 billion• wavelength = 500 nm = 5 x 102x10-9 m = 5 x 10-7 m• Distance = 1 cm =10-2m• Hence number = distance/wavelength = 10-2m /(5 x 10-7 m) = 105/5 = 104/ 0.510,000 x 2 = 20,000 wavelengths in a cm3 clicker questions1. Which of the light waves has the longest wavelength?a) b) or c) ?2. Which of the light waves is brightest?a) b) or c) ? 3. Which of the light waves has the highest speed in empty space?a) b) c) ord) They all have the same speeda)b)c)2323Lecture 4 – Chapter 1 & 2 •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 hereStart Chapter 224Sources of light• Flame (atomic emission) • Incandescent• Gas discharge (neon or mercury atomic emission)• Fluorescent (mercury gas discharge + phosphor)• Plasma TV (phosphors have color)• Light emitting diode (LED)• LaserAll sources involve moving electrons ! Demo: LED headlamp25Flame and gas dischargehave excited atoms that emit• Emission of light • Absorption of light• Atomic electron starts at high energy level• Atomic electron ends at a lower energy level• Extra energy is carriedoff by light (photon)• Atomic electron at high energy level (atom gains energyfrom light)• Atomic electron at a lower energy levelLight (a photon)hits an atomDemo: neon light26Hot materials emit blackbodyradiation (incandescence)Object temperature emission:People 300 C infraredCharcoal fire 2000 C dull redTungsten filament 3000 C reddish whiteSun 6000 C orange whiteBrighest star 10,000 C bluish white• Note that hotter objects emit bluer light (shorter wavelength). • All wavelengths are emitted (a whole spectrum), some wavelengths are emitted more. Demo: bulb on dimmer gets redder27Higher temperatures have peak emission at shorter wavelengthsFluorescent lamp(based on fluorescent mineral coating)Fluorescent coating absorbs UV photons from mercury gas discharge and emits visible light photons with high efficiency. Calcium fluoride is fluorescent. 28Lifetime: 8-15 times longer than incandescentEnergy consumption: 3 – 5 times lessCost: 3 – 10 times moreDemo: fluorescent minerals29Chapter 2 – Geometrical Optics1. Shadows2. Reflection3. Refraction4. DispersionWe are here301. Shadowsa. Point source or diffuse source b. Umbra and penumbra c. How tall is my shadow? d. Pinhole cameraPoint source or diffuse source?• Point-like source of light is small in size.• Diffuse source of light has a large area.• Size of a source is measured by angle to decide.