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Learn about the importance of light, electromagnetic wave properties, colors, electromagnetic spectrum, energy transmission, atom structures, electron behavior, spectra types, Doppler shift, and atmospheric effects.
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Light and Atoms Part I
Light • Importance • light is the only way of getting information • most experiments cannot be setup on Earth
Background • Electricity • force between electrical charges • Magnetism • force between magnetic poles • Electricity and Magnetism are related • one can produce the other • class demos
What is Light? • Electromagnetic Wave • wavelength (l) • distance between crests • frequency (f) • number of crests/second • speed • v = lf • same for all wavelengths • same for all frequencies
What is Light? • Color • related to wavelength • longer l - redder • shorter l - bluer • visible light • white light • all colors
What is Light? • The Electromagnetic Spectrum • Visible light small portion of spectrum • longest l • radio waves • shortest l • gamma rays • The Spectrum • radio waves, infrared, visible light, ultraviolet, x-rays, gamma rays
What is Light? • Carries Energy • shorter wavelengths - more energy • longer wavelengths - less energy • Intensity • energy per time per area • inverse square law
Wien’s Law • Blackbody • perfect absorber of energy • energy radiated depends on temp • Color related to temperature • peak l depends on temp
Types of Spectra • Continuous • High density hot gas, liquid, or solid • blackbody would give this type • continuous rainbow • Light at all wavelengths
Types of Spectra • Emission Spectra • Hot low density gas • Light only at some wavelengths • pattern of bright lines • Absorption Spectra • Cool gas between observer and light source • Light missing or dimmer at some wavelengths • continuous spectra with dark lines
Atoms • Structure of Atoms • nucleus • number of protons in nucleus determines kind of element • orbiting electrons • classical problem
Electrons and Spectra • only certain orbits allowed • each orbit has certain energy • electrons jump between allowed orbits • down to lower orbit • releases energy • emits light • emission spectra • up to higher orbit • absorbs energy • absorbs light • absorption spectra
Electrons and Spectra • electron orbits are unique • Elements have own distinct spectra • Elements can be identified
The Doppler Shift • Motion causes shift in wavelength • size of shift proportional to speed • source moving away • shifted to longer wavelengths - redshift • source approaching • shifted to shorter wavelengths - blueshift
The Doppler Shift • observer approaching source • shifted to shorter wavelengths - blueshift • observer moving away from source • shifted to longer wavelengths -redshift • If source and observer are approaching • wavelengths decrease • If source and observer are moving farther apart • wavelengths increase
Atmospheric Effects • Earth"s atmosphere absorbs some l • visible light not absorbed • IR, UV, X-ray, & gamma absorbed • Atmospheric window • wavelengths that can pass through atmosphere