Physics 202: Introduction to Astronomy – Lecture 5

1. Physics 202: Introduction to Astronomy – Lecture 5 Carsten Denker Physics Department Center for Solar–Terrestrial Research

2. 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 Chapter 2.1 – 2.6 Center for Solar-Terrestrial Research

3. Coulomb’s Law Coulomb’s law Gravitational force Coulomb’s law Superposition principle Center for Solar-Terrestrial Research

4. Electromagnetic Waves Center for Solar-Terrestrial Research

5. The Interaction of Light and Matter Center for Solar-Terrestrial Research

6. 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. Center for Solar-Terrestrial Research

7. Electromagnetic Spectrum Center for Solar-Terrestrial Research

8. Kirchhoff’s Laws • A 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. Center for Solar-Terrestrial Research

9. 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 Center for Solar-Terrestrial Research

10. Spectroscopy • Prisms • Diffraction gratings • Transmission grating • Reflection grating Resolving power Center for Solar-Terrestrial Research

11. 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 Center for Solar-Terrestrial Research

12. Hydrogen Atom Planetary model of the hydrogen atom? Center for Solar-Terrestrial Research

13. 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. Center for Solar-Terrestrial Research

14. 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. Center for Solar-Terrestrial Research