Kirchoff’s Laws and Emission Spectra

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Kirchoffs Laws and Emission Spectra

• 3 types of spectra
• Energy levels
• Hydrogen-alpha (H?)
• HW Ch 4 RD 11-13, 16, P 6-9

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Gustav Robert KirchoffGerman1824-1887
http//ffden-2.phys.uaf.edu/211.fall2000.web.proje
cts/Jeremie20Smith/images/kirchoff.gif
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Kirchoffs Laws - 3 types of spectra

• Continuous (a.k.a. Continuum, Blackbody
  radiation)
• Emission
• Absorption
• Kirchoff knew what type of object created each
  type of spectrum, but didnt know why

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http//www.atmos.albany.edu/student/davis/Astronom
y/Image14.gif
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Continuous Spectrum

• Continuous, continuum, blackbody
• Hot dense object
• All colors
• Examples stars are nearly blackbody, light
  bulbs, people, etc.
• We already discussed why hot objects do this.

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http//fuse.pha.jhu.edu/bianchi/kit1/cont.gif
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Emission Spectrum

• Hot thin gas
• Only a few select colors
• Examples some fluorescent lights, the spectrum
  tubes used in lab, neon lights, warm gas clouds
  in space

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http//astronomy.nmsu.edu/nicole/teaching/ASTR110/
lectures/lecture19/pics/emission_spectra.gif
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Absorption Spectrum

• Hot dense object blocked by cool thin gas
• All colors except a select few
• Examples nearby gas cloud blocks a farther star,
  nearer galaxy blocks a far quasar, sunglasses
  block sunlight, Earths atmosphere blocks sunlight

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http//www.physics.umd.edu/courses/Phys401/bedaque
06/discrete_spectra.jpg
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http//escience.anu.edu.au/lecture/cg/Color/Image/
sunSpectrum.png
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http//chinook.kpc.alaska.edu/ifafv/lecture/misce
ll/fraunhof/sun_spectrum.jpg
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http//outreach.atnf.csiro.au/education/senior/ast
rophysics/images/spectra/spectypes2.gif
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Johann Jakob BalmerSwiss1825-1898
http//upload.wikimedia.org/wikipedia/commons/5/51
/Balmer.jpeg
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http//homepage.mac.com/dtrapp/chemGraphics.f/Hydr
ogenSpectra.jpg
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http//www.solarobserving.com/pics/hydrogen-spectr
a.jpg
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Balmer series

• Hydrogen puts out light in very specific colors
• Wavelengths of colors related to 1/22-1/n2, where
  n3, 4, 5
• Balmer did not yet understand why.

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Johannes RydbergSwedish1854-1919
http//zahav.elementy.ru/images/eltbio/rydberg_joh
annes_robert_160.jpg
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Bohr Atom and Energy Levels

• Each level of electron shell corresponds to an
  amount of energy.
• Electrons can jump from one shell to another by
  emitting or absorbing a photon.
• The frequency of the photon indicates the energy
  difference between the levels (Eh?,
  h6.610-34Js).

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http//www.daviddarling.info/images/hydrogen_spect
rum.gif
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Rydberg Formula

• Describes what wavelengths will be emitted from
  which transitions

RH1.09107m-1
http//en.wikipedia.org/wiki/Rydberg_formula
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H-alpha

• Balmer series referred to as H
• First line H-? (alpha) is 3-2
• Second H-? (beta) is 4-2
• Third H-? (gamma) is 5-2
• Etc.
• Lyman
• Lyman-alpha is 2-1
• Lyman-beta is 3-1, etc.
• Paschen is n-3
• Brackett is n-4
• Pfund is n-5
• Humfreys is n-6

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Calculations
n, m wavelength frequency energy
H-alpha
H-beta
H-gamma
Lyman-alpha
Lyman-beta
Paschen-alpha