1. Atom and Light ASTR 14: Exploring the Universe

2. 2 Outline Nature of Light Basic Properties of Light Atomic Structure Periodic Table of the Elements Three Types of Spectra Interaction of Light and Matter Useful Application – Doppler Effect

3. 3 Nature of Light What is the “Nature” of Light? Observed Properties of Light –reflection, refraction, diffraction, & interference Wave Properties –reflection, refraction, diffraction, & interference Particle Properties –reflection, refraction Particle-Wave Duality

4. 4 Wave Properties of Light Wave Properties –diffraction –Interference Young’s Double-Slit Experiment (1801)

5. 5 Wave Properties of Light Electromagnetic Waves –wavelength (meter) –frequency (cycles per second = Hertz = Hz) Speed of Light –constant within a medium –absolute speed –3.0 x 10 8 m/s in vacuum Fizeau-Foucault Method (1850)

6. 6 Electromagnetic Spectrum Speed of Light = wavelength x frequency C = x

7. 7 Particle Properties of Light Max Planck (1900) –Blackbody Radiation –Electromagnetic energy (radiation) is emitted in discrete, particlelike packet. Albert Einstein (1905) –Re-interpret Planck’s result –Photoelectric Effect –Light as particles -- photons Energy of a Photon –The energy of a photon is proportional to its frequency.

8. 8 Blackbody Radiation

9. 9 Wien’s Law –The wavelength of maximum emission of a blackbody is inversely proportional to its temperature. Stefan-Boltzmann Law (Box 5-2) –The energy flux (power per unit area) of a blackbody is proportional to the 4 th power of its temperature.

10. 10 Atomic Structure Rutherford’s Experiment (1910) Rutherford’s Model of the Atom Atomic Structure –cloud of electrons –nucleus protons neutrons

11. 11 Atomic Structure

12. 12

13. 13 Three Types of Spectra

14. 14 Interaction of Light and Matter Kirchoff’s 1 st Law –A hot opaque body, such as a perfect blackbody, or a hot, dense gas produces a continuous spectrum. Kirchoff’s 2 nd Law –A hot, transparent gas produces an emission line spectrum. Kirchoff’s 3 rd Law –A cool, transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum. The absorption lines in the absorption line spectrum of a particular gas occur at exactly the same wavelengths as the emission lines in the emission line spectrum of the same gas. Types of spectra of matter can produce is dictated by the physical condition/state of the matter.

15. 15 Interaction of Light and Matter Bohr Model of Hydrogen Atom –energy levels or states Quantum Rules –Electron can only occupy at discrete energy level. –Electron can jump from one energy level to another only if it gains or loses a specific amount of energy equal to the differences of the levels.

16. 16 Interaction of Light and Matter Electron Transitions in Hydrogen

17. 17 Interaction of Light and Matter

18. 18 Interaction of Light and Matter States of Matter

19. 19 An Example

20. 20 Doppler Effect Christian Doppler (1842) The apparent change in wavelength or frequency of radiation due to relative motion between the source and the observer along the line-of-sight. If the relative motion between the source and the observer is moving away from each other, the observed spectral line is longer than the lab wavelength, it is called a redshift. If the relative motion between the source and the observer is moving towards each other, the observed wavelength is shorter than the lab wavelength, it is called a blueshift.  = wavelength shift o = lab wavelength V = radial velocity c = speed of light + = redshift - = blueshift

21. 21 Doppler Effect Stationary SourceMoving Source

22. 22 An Example