1. Atom and Light Lancelot L. Kao Updated: Jan 24, 2010

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

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 Three Types of Spectra

9. 9 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.

10. 10 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

11. 11 Doppler Effect Stationary SourceMoving Source

12. 12 An Example

13. 13 Relativistic Doppler Effect  = observed wavelenght  = lab wavelength v = radial velocity c = speed of light + = redshift - = blueshift

14. 14 Atomic Structure Rutherford’s Experiment (1910) Rutherford’s Model of the Atom Atomic Structure –cloud of electrons –nucleus protons neutrons

15. 15 Atomic Structure

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17. 17 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.

18. 18 Interaction of Light and Matter Electron Transitions in Hydrogen

19. 19 Interaction of Light and Matter

20. 20 Blackbody Radiation

21. 21 Blackbody Radiation Wien’s Law –The wavelength of maximum emission of a blackbody is inversely proportional to its temperature. Stefan-Boltzmann Law –The energy flux (power per unit area) of a blackbody is proportional to the 4 th power of its temperature.

22. 22 An Example

23. 23 Interaction of Light and Matter States of Matter