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Light Light
PSC 203 PSC 203
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Overview Overview
(^) In this section:In this section: (^) What is light?What is light? (^) What is the EM Spectrum?What is the EM Spectrum? (^) How is light created?How is light created? (^) What can we learn from light?What can we learn from light? 33
In-class activity In-class activity
(^) Discuss your answers in groups of 2Discuss your answers in groups of 2 (^) Think of as many examples light sourcesThink of as many examples light sources that you can think of. that you can think of. (^) List as many as you can on your paper.List as many as you can on your paper. (^) Be prepared to turn this list in.Be prepared to turn this list in. 44
What is light? What is light?
(^) light is an electro-magnetic wavelight is an electro-magnetic wave (^) electric and magnetic fields oscillateelectric and magnetic fields oscillate (^) carries energy as it travelscarries energy as it travels (^55)
What are waves? What are waves?
(^) If light is a wave we need to understandIf light is a wave we need to understand what a wave is. what a wave is.
Waves Waves
(^) all waves have three related propertiesall waves have three related properties (^) speed:speed: (^) how fast the wave moveshow fast the wave moves (^) wavelength:wavelength: (^) the distance between peaksthe distance between peaks (^) frequency:frequency: (^) how often a peak passes byhow often a peak passes by
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Speed Speed
(^) the “speed of light” is very fastthe “speed of light” is very fast (^) c = 300,000,000 m/s = 3 x 10c = 300,000,000 m/s = 3 x 10^88 m/sm/s (^) c = 671,000,000 mi/hrc = 671,000,000 mi/hr 88
Wavelength Wavelength
(^) the distance between peaksthe distance between peaks 99 (^) You can see theYou can see the wavelength of an wavelength of an ocean wave ocean wave (^) You can’t “see” theYou can’t “see” the wavelength of light wavelength of light but it works the but it works the same way same way 1010
Frequency Frequency
(^) how many peaks pass a fixed point duringhow many peaks pass a fixed point during a set amount of timea set amount of time (^) most commonly measured in Hz (Hertz)most commonly measured in Hz (Hertz) (^) 1 Hz = 1 wave peak per second1 Hz = 1 wave peak per second
Wavelength vs frequency Wavelength vs frequency
(^) Wavelength and frequency are relatedWavelength and frequency are related (^) Frequency increases -> wavelength decreasesFrequency increases -> wavelength decreases (^) Frequency decreases -> wavelength increasesFrequency decreases -> wavelength increases
Energy of Light Energy of Light
(^) As frequency increases, so does theAs frequency increases, so does the energy (takes more energy to create highenergy (takes more energy to create high frequencies)frequencies) (^) High frequency = high energyHigh frequency = high energy (^) Low frequency = low energyLow frequency = low energy (^) Wavelength is oppositeWavelength is opposite (^) High energy = short wavelengthHigh energy = short wavelength (^) Low energy = long wavelengthLow energy = long wavelength
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Appearance Appearance
(^) Objects “look” different depending onObjects “look” different depending on what type of light is used what type of light is used (^) Need special tools to see different types ofNeed special tools to see different types of light light (^) We can get new information by looking atWe can get new information by looking at different types of light different types of light 2020
Object in various light Object in various light
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Infrared Infrared
(^) Shows heat levelsShows heat levels (^) IR goes through dust and smokeIR goes through dust and smoke 2222
X-rays X-rays
(^) Emitted only by high energy processesEmitted only by high energy processes (^) Can pass through lower density materialsCan pass through lower density materials
UltravioletUltraviolet
(^) Emitted by medium-high energy sourcesEmitted by medium-high energy sources (^) Flowers show highlighted portions nearFlowers show highlighted portions near the pollen when viewed in UV (bees see the pollen when viewed in UV (bees see UV light too) UV light too) (^) Old bruises on human skin can sometimesOld bruises on human skin can sometimes be seen in UV but not visible be seen in UV but not visible
Radio Radio
(^) Emitted by cold hydrogenEmitted by cold hydrogen (^) Can pass through solid objects (like walls)Can pass through solid objects (like walls)
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Types of SpectraTypes of Spectra
(^) When we break light into its spectrum itWhen we break light into its spectrum it doesn’t always look the same doesn’t always look the same (^) It depends on how the light wasIt depends on how the light was generated generated 2626 (^) light is a form of energy...light is a form of energy... (^) energy has to be transformed into lightenergy has to be transformed into light from some other formfrom some other form (^) sources are categorized by the originalsources are categorized by the original energyenergy
Formation of light Formation of light
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Incandescent Blackbody Incandescent Blackbody
(^) Light generated from thermal energyLight generated from thermal energy (^) Light emitted at all wavelengthsLight emitted at all wavelengths (^) Shape depends only on temperatureShape depends only on temperature (^) As temp rises …As temp rises … (^) Intensity increasesIntensity increases (^) Peak shifts in color toward blue sidePeak shifts in color toward blue side 2828
Blackbody examples Blackbody examples
(^) PeoplePeople (^) Electric StoveElectric Stove (^) Blow torchBlow torch
Atomic emission Atomic emission
(^) Light generated from atomic energyLight generated from atomic energy (^) Energy transitions inside atoms/moleculesEnergy transitions inside atoms/molecules (^) Light is only at specific wavelengths/energiesLight is only at specific wavelengths/energies (^) Spectra gives information about the atomsSpectra gives information about the atoms
