Quantum Mechanics

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Quantum Mechanics

• A Summary

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Max Planck - 1900

• Tried to explain the nature of radiation emitted
  by a Black Body.
• His idea involved the energy being exchanged in
  lumps or quanta.
• Energy of a quantum given by E h?
• Planck thought of this as just a mathematical
  trick.

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Albert Einstein - 1905

• Took Plancks idea and pushed it further.
• Stated that e/m radiation light actually
  travelled as lumps or particles photons.
• Used this idea to explain the photoelectric
  effect the emission of electrons from
  illuminated metal surfaces.

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Niels Bohr - 1913

• Tried to solve the problems associated with the
  nuclear model of the atom by quantising electron
  orbits.
• Only certain orbits, obeying particular rules,
  were allowed to the electron stationary states.
• No radiation was emitted/absorbed if the electron
  stayed in such an orbit, only if the electron
  jumped from one orbit to another.

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Franck and Hertz - 1914

• Carried out an experiment which clearly
  demonstrated the existence of Bohrs stationary
  states.
• Further evidence came from study of line spectra.

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Wolfgang Pauli - 1925

• Invented the Exclusion Principle no 2 electrons
  are allowed to be in exactly the same quantum
  state.
• So each stationary state can only contain 2
  electrons one spin-up and the other
  spin-down. Any more electrons must go into
  higher orbits.
• The pattern resulting from this explains the
  existence of the Periodic Table.

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Louis de Broglie - 1923

• Einstein had already shown that light sometimes
  seemed to behave like waves and sometimes like
  particles.
• De Broglie suggested that tiny particles, such as
  electrons, could also behave like waves
  wave-particle duality.
• De Broglie wavelength ? h/mv

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Thomson and Davisson - 1927

• Carried out experiments which demonstrated that
  electrons could indeed behave like waves they
  could form diffraction patterns.

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Werner Heisenberg - 1925

• Used matrices (arrays of numbers) to provide a
  complete mathematical description of the way
  electrons behave.
• Very abstract theory not initially popular.
• Also realised that quantum mechanics implies an
  unavoidable limitation on what we can
  know/measure about a particle the Uncertainty
  Principle.

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Erwin Schrodinger - 1926

• Used the waves concept of de Broglie and
  developed a wave equation that governs the
  behaviour of small particles.
• But what did the solution of this the wave
  function actually mean?
• Max Born suggested that it represented the
  probability that the particle could be found at a
  certain spot.

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Paul Dirac - 1928

• Produced a generalised version of quantum
  mechanics, adding in both relativity and electron
  spin.
• Applied this to e/m radiation as well as
  particles ? quantum electrodynamics.
• Predicted the existence of the positron.
• Positron discovered by Carl Anderson 1932.