Lecture18_10 - Physics19 GreatIdeasofPhysics...

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Click to edit Master subtitle style Physics 19 Great Ideas of Physics Lecture 18: Waves and Uncertainty
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Don’t Panic… There is a theory which states that if ever  anybody discovers exactly what the Universe  is for and why it is here, it will instantly  disappear and be replaced by something even  more bizarre and inexplicable.  There is another theory which states that this  has already happened.
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Last Time Problems with classical physics multiply… Thermal radiation requires quantization of energy Photoelectric effect requires a particle model of light Atomic structure and line spectra Bohr’s model of the Hydrogen atom Electrons occupy special (stable) states of fixed energy Spectral lines correspond to transitions between stable  states Photon energy = (E2 – E1) 1/Wavelength = (constant)×(1/n12 – 1/n22)
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The Wave Nature of Matter In his 1924 doctoral dissertation, the Louis de  Broglie provided an important new idea The photon theory of light was now widely  accepted; in it, a photon with wavelength N  carries  momentum as well as energy: p = h/ de Broglie proposed turning this relationship  around.  He suggested that a particle  with 
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Proving the Wave Nature Two Americans, Davisson  and Germer, as well as J.J.  Thomson’s son showed  soon after that electrons  can be diffracted and  exhibit interference, just  like waves de Broglie won the Nobel  Prize in 1926 Two years after his PhD! Diffraction of X-rays Diffraction of electrons with identical wavelength
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What’s Your Wavelength? In principle, even macroscopic objects have a de  Broglie wavelength. For a 60.0 kg person, walking  at 2.00 m/s:   = h/p = h/mv   = (6.63 @ 10-34 J s)/(60.0 kg)(2.00 m/s)   = 5.52   10-36 m Because Planck’s constant is so small, quantum  effects are not observable in macroscopic objects For an electron moving at 2.00 m/s:   = 3.64   10-4 m (1/3 mm)
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Erwin Schrödinger (1887-1961) Austrian theorist Initially worked on statistical  mechanics, following Boltzmann’s  probability theory Fled Germany for Austria when 
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Lecture18_10 - Physics19 GreatIdeasofPhysics...

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