Tuesday 911

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2/23 Tuesday 9/11
Problem Set PS 0 Due Today Today Electroma
gnetic waves Blackbody radiation
Photoelectric effect
Hydrogen spectra Tomorrow Mathematica Lab Two
groups 100PM - 130 PM
130 PM to 300 PM

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Electromagnetic waves-MatterInteractions

• Electromagnetic waves
• Blackbody radiation
• Photoelectric Effect
• Hydrogen gas spectra

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Electromagnetic waves

• Electromagnetic waves are made up of oscillating
  electric, E, and magnetic, B, fields and produced
  by accelerated charges
• E displaces charged particles along the direction
  of the field
• B rotates charged particles around the direction
  of the field
• E and B are perpendicular to each other

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Electromagnetic Wave
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Blackbody Radiation

• 1782 A heated metal at temperature T emits
  radiation of almost all frequencies.
• Blackbody is an ideal system that absorbs and
  emits all frequencies
• 1896 Wien - Theory High n
• 1897 Paschen - Experiment at High n
• 1899 Wiens Law T lmax constant
• 1899 Stefan-Boltzman Law R s T4
• 1900 Lummer and Pringshein-Low n

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Blackbody Radiation
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Comparison
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Plank solved the problem (1900)

• It was an act of desperation. For six years I
  had struggled with Blackbody theory. I knew the
  problem was fundamental and I knew the answer. I
  had to find a theoretical explanation at any
  cost, except for the inviolability of the second
  law of thermodynamics
• Plank 1930

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PLANK vs experiment
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Photoelectric Effect
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Photoelectric Effect

• First observed by H. Hertz
• Visible or ultraviolet light shone on a clean
  metal surface can cause ejection of electrons
  from the surface

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Experimental setup
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Classical Theory Predictions

• The energy of the ejected electron is
  proportional to the intensity of the light.
• Electrons are rejected for any frequency

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Minimum Frequency
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Simple theory
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Einstein theory (1905)
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Gas spectra
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Spectroscopy
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Spectra
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Hydrogen gas spectra
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Bohrs Assumptions (1913)

• I - atoms can exist in stationary states without
  radiating energy
• II - Transitions between these states can occur
  by absorption or emission of radiation
• III - Angular momentum is quantized

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Energy is quantized
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Transition between energy levels
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Spectra from Bohr model
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Correction

• We need to consider that the rotation is around
  the center of mass. Therefore we need to
  exchange the mass of the electron by the reduced
  mass

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Heat CapacityatLow Temperature

• At high temperature
• Cv 3 R
• At low temperature
• Cv depends on T
• Classical Theories cannot
• explain

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Wave property

• Interference of waves

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Wave property

• Interference of waves

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Electron interference (1961)

• Modern experiment with electrons

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Interference

• In a modern experiment (1989) with electrons, one
  can shoot one electron at the time or all at
  once. The final pattern is the same
• Tonomura, A., Endo, J., Matsuda, T, and Kawasaki,
  T, Am. J. Phys., 57,117-120 (1989)

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