21-) - ASTR100Lg LastTime Waveslanguage/description...

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ASTR 100Lg Last Time Waves – language/description   - Intuition Light – it is a wave Newton o “light is a particle as waves can’t go through a vacuum” Electric/Magnetic Field WILL go through a vacuum James Clerk Maxwell (1831-1879) Wrote down/figured out fundamental equations of electromagnetism Showed that… o A) There could be self sustaining electromagnetic waves Faraday postulated that electric waves sustained magnetic waves, vice  versa One cannot exist without the other o B) Calculated speed c = 3.00x10 8  m/s o C) Conjectured that light was precisely such a wave Electromagnetic Spectrum
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Next: Sources of Radiation A) stars o Black Body Radiation B) Nebulae    clouds of glowing gas o Emission Line Spectrum Reminder: Temperature Standard/Familiar                      Ice/Water            Boiling water Fahrenheit, ºF                           32ºF                     212ºF Celius/Centigrade, ºC                 0ºC                      100ºC o Choice is arbitrary/culturally dependent Can we find a better temperature scale   more universal? Better notion of “0” Gas Laws : Charles law o Study a gas at constant pressure Volume increases with temperature When balloon is dropped in liquid nitrogen, the balloon shrivels up Notion of the “ideal gas”
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Will go down to zero volume at temperature of  -273ºC Model: Classical molecule motion stops at -273º William Thomson (1824-1907) Lord Kelvin Use the celsius scale but reset the zero to -273ºC o The Kelvin scale o T Kelvin  = T Celcius  + 273    T = 0K For example, this room is 15ºC OR 288K o Kelvin scale/absolute temperature Absolute 0 = 0K = -273ºC Henchforth, temp will be on Kelvin scale Radiation Black Body radiation Make precise: o If you heat up a body… A) Red hot   yellow   white B) Energy output increase Dull   brighter
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Black Body o Utterly non-reflective o Does not reflect its environment o Anything it emits is an intrinsic property of that body o Example: Stars are black bodies Wien’s law      (Black bodies) λ dominant  = 0.0029m/ T Kelvin o Bigger T   shorter  λ o Example: Sun is yellow λ dominant  = yellow            = 500 nm (5x10 -7 m) T = 0.0029/(5x10 -7 m) = 5800 K = 5527ºC o Example: Star that has a temp of 20000K λ dominant  = 0.0029/20000K = 1.45x10 -7 m = 145nm Ultraviolet Star looks white (bluish tint) λ dominant  is not the only important wavelength!
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21-) - ASTR100Lg LastTime Waveslanguage/description...

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