physics 202: introduction to astronomy – lecture 5
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Physics 202: Introduction to Astronomy – Lecture 5. Carsten Denker Physics Department Center for Solar–Terrestrial Research. Light and radiation Spectrum: radio, infrared, visible, ultra-violet, X-rays, gamma-rays Waves: wavelength, frequency, amplitude, and period Electromagnetic waves - PowerPoint PPT PresentationTRANSCRIPT
Physics 202: Introduction to Astronomy – Lecture 5
Carsten Denker
Physics DepartmentCenter for Solar–Terrestrial
Research
February 1, 2006 Center for Solar-Terrestrial Research
Chapter 2.1 – 2.6 Light and radiation Spectrum: radio,
infrared, visible, ultra-violet, X-rays, gamma-rays
Waves: wavelength, frequency, amplitude, and period
Electromagnetic waves
Electromagnetism
Blackbody radiation Radiation laws Spectroscopy Emission and
absorption lines Spectral line
formation Bohr model of
atoms Hydrogen spectrum Kirchoff’s laws
February 1, 2006 Center for Solar-Terrestrial Research
Coulomb’s Law
Superposition principle
Coulomb’s law
Gravitational force
Coulomb’s law
1 22
q qF k
r
1 22
mmF G
r
1 22
0
1
4
q qF
r
9 2 2
0
18.99 10 N m C
4k
12 2 1 2
0 8.85 10 C N m
1,net 12 13 14 1nF F F F F
February 1, 2006 Center for Solar-Terrestrial Research
Electromagnetic Waves
February 1, 2006 Center for Solar-Terrestrial Research
The Interaction of Light and The Interaction of Light and MatterMatter
February 1, 2006 Center for Solar-Terrestrial Research
Infrared Radiation
In 1800, William Herschel (1738 –1822) extended Newton's experiment of separating chromatic light components via refraction through a glass prism by demonstrating that invisible "rays" existed beyond the red end of the solar spectrum.
February 1, 2006 Center for Solar-Terrestrial Research
Electromagnetic Spectrum
February 1, 2006 Center for Solar-Terrestrial Research
Kirchhoff’s LawsA hot (< 0 K), dense gas or solid object
produces produces a continuous spectrum with no dark spectral lines.
A hot, diffuse gas produces bright spectral lines (emission lines).
A cool, diffuse gas in front of a source of a continuous spectrum produces dark spectral lines (absorption lines) in the continuous spectrum.
February 1, 2006 Center for Solar-Terrestrial Research
Spectroscopy The English chemist and
physicist William Hyde Wollaston (1766 – 1828) noticed dark lines in the spectrum of the Sun while investigating the refractive properties of various transparent substances
Joseph von Fraunhofer (1787-1826) independently rediscovered the “dark lines” in the solar spectrum
February 1, 2006 Center for Solar-Terrestrial Research
Spectroscopy Prisms Diffraction gratings
Transmission grating Reflection grating
sin and 1, 2, 3, ...d n n
nN
nN
Resolving power
February 1, 2006 Center for Solar-Terrestrial Research
The Bohr Model of the Atom Wave–particle duality of light Rutherford 1911 Au: It was quite the most
incredible event that ever happened to me in my life. It was almost as incredible as if you fired a 15–inch shell at a piece of tissue paper and it came back an hit you. discovery of a minute, massive, positively charged atomic nucleus
Proton: mp = 1836 me
February 1, 2006 Center for Solar-Terrestrial Research
Hydrogen Atom1
2
1 1 1 and 109677.585 0.008 cm
4H HR Rn
2 2
1 1 1 and HR m n
m n
m = 1 UV [122, 103, 97, …] nm Lyman
m = 2 Visible [656, 486, 434, …] nm Balmer
m = 3 IR [1875, 1282, 1094, …] nm Paschen
m = 4 IR [4051, 2625, 2165, …] nm Brackett
m = 5 IR [7458, 4652, …] nm Pfundt
Planetary model of the hydrogen atom?
February 1, 2006 Center for Solar-Terrestrial Research
Kirchhoff’s Laws Revisited A hot, dense gas or hot solid object produces a continuous
spectrum with no dark spectral lines. This is the continuous spectrum of black body radiation, described by the Planck functions B(T) and B(T), emitted at any temperature above absolute zero. The wavelength max at which the Planck function B(T) obtains its maximum is given by Wien’s displacement law.
February 1, 2006 Center for Solar-Terrestrial Research
Kirchhoff’s Laws Revisited (cont.)
A hot, diffuse gas produces bright emission lines. Emission lines are produced when an electron makes a downward transition from a higher to a lower orbit. The energy lost by the electron is carried away by the photon.
A cool, diffuse gas in front of a source of continuous spectrum produces dark absorption lines in the continuous spectrum. Absorption lines are produced when an electron makes a transition from a lower to a higher orbit. If the incident photon in the continuous spectrum has exactly the right amount of energy, equal to the difference in energy between a higher orbit and the electron’s initial orbit, the photon is absorbed by the atom and the electron makes an upward transition to the higher orbit.