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Unformatted text preview: 9/2/10 1 ©2010 W.W. Norton & Company, Inc. Light and Matter Interactions What happens when light and matter interact? Easiest possibility = reflection (why is an orange orange ?) Interaction of light with matter means the creation (emission) or annihilation (absorption) of photons by atoms and molecules. ©2010 W.W. Norton & Company, Inc. Atoms and Light • Atoms have a dense nucleus of protons and neutrons . • Electrons surround the nucleus in a “cloud.” ©2010 W.W. Norton & Company, Inc. Atoms and Light • Electrons can have certain energies; other energies are not allowed. • Each type of atom has a unique set of energies. • Energy level diagram. Energy Levels • Electrons in an atom exist in well-defined energy levels characterized by precise values of energy (they are quantized). • When matter is at rest (0 K) all electrons are in their lowest level ( ground state ). 9/2/10 2 Electron Orbits • Electron orbits in the electron cloud are restricted to very specific radii and energies. r 1 , E 1 r 2 , E 2 r 3 , E 3 • These characteristic electron energies are different for each individual element. Absorption When a ray of light comes in from an outside source and hits an atom, it may only be absorbed if it is the correct energy to move the electron up to one of the possible energy levels....
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This note was uploaded on 02/02/2012 for the course ASTR 5 taught by Professor Rhee during the Spring '11 term at Mt. SAC.
- Spring '11