AST- 105 1st EditionLecture 6Outline of Last LectureI. SpectroscopyII. Kirchoff’s LawsOutline of Current LectureI. Kirchoff’s Laws (cont’d) II. The Spectroscopic MethodIII. Emission and Absorption of Photons by Atoms Current LectureI. Kirchoff’s Laws a. Kirchoff’s Law 1- a hot solid object or dense gas produces a continuous spectrum.i. Complete rainbowii. All wavelengths seeniii. No spectral linesiv. Examples:1. Incandescent lights2. Heated bar of iron3. Ideal Black Bodyb. Kirchoff’s Law 2- a low-density, hot gas produces an emission line spectrum.i. Series of bright lines ii. No emission between linesiii. Examples:1. Neon signs2. Chromospheres of the Sun3. Bright interstellar cloudsc. Kirchoff’s Law 3- a low-density, cooler gas produces an absorption line spectrum when viewed in front of a hotter continuous source. i. Continuous spectrum with dips at a certain wavelengthii. Dark lines among colors of rainbowiii. Examples: 1. Photosphere of the Sun2. Other stars3. galaxiesII. The Spectroscopic Methoda. The Spectroscopic Method- every element or compound produces a unique set of lines…a fingerprint. i. Wavelengths of lines are calculated theoretically in lab. ii. Identification of lines in spectra of celestial objects.iii. Gives composition and physical state of abject.III. Emission and Absorption of Photons by Atomsa. Atomic Structure:i. Nucleus: central structure, protons, and neutronsii. Electrons: orbit about nucleusb. Normal Hydrogen Atom:i. Nucleus: 1 protonii. 1 electron orbits the nucleusc. Bohr Model: only certain size electron orbits are possible: 1, 2, 3, 4…i. Size of orbit determines energy level: larger orbit = higher energyd. Photons are emitted or absorbed when an electron changes orbiti. Larger orbit to smaller orbit (higher energy to lower energy) photon emitted.ii. Smaller orbit to larger orbit (lower energy to higher energy) photon absorbed.iii. Photon energy- energy difference between the two orbitse. Ionization- atom absorbs sufficiently energetic photon to cause electron to jump out of the
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