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Lecture04 - Previous Lecture Stellar Brightness Wave nature...

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Previous Lecture – Stellar Brightness Wave nature of light c = f λ Spectrum: intensity as a function of wavelength Photometric filter system: UBVRI Luminosity, Flux, and Inverse-Square Law F = L / (4 π d 2 ) Thermal sources and the blackbody spectrum Wien’s law: λ max 1 / T Stefan-Boltzmann Law: L = 4 π R 2 σ T 4 Stellar spectral classification
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Light – Revisited Most, but not all, aspects of light fit a wave model Early in the 20 th century, physicists realized that a particle aspect was also required Einstein – photoelectric effect – 1905 Nobel Prize Particles of light are called photons photon energy: E = h f = h c / λ Planck’s constant (h): h = 6.6 x 10 -34 joule sec color is related to energy blue light has higher energy photons
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Atomic Structure Two component atom: nucleus and electrons held together by electric force structure analogous to solar system Nucleus – Sun Electrons – Planets Electric force – Gravity
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Atomic Structure (continued) Crucial difference: in atom orbits are quantized only certain orbits allowed orbit size is related to energy (like solar system) so energy is also quantized
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Atomic Structure (continued) Electrons can change energy levels exactly the energy difference between the levels must be supplied (or removed) to move up (or down) electrons try to move to lowest energy levels possible mechanisms to higher or lower energy levels: collisions between atoms interaction with light (photons)
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