covered: deBroglie wavelengths double-slit diffraction Rutherford planetary model Bohr Model Correspondence Principle This seems to be primarily historical motivation. The correspondence principle, I'm not sure I've ever attempted to compute for even a simple system. Hmm... I see the note here "What is the Correspondence principle? Derive the quantum condition from it." I don't know what is meant by the "quantum condition". I guess just that the states of a system are quantized. I have no clue how I would show that using the correspondence principle. Should ask about this. planck determined that light transferred energy in "packets". De Broglie suggested a certain nature to the packets, that the wave nature of light was also applicable to matter. These ideas suggested that matter and light both exhibit properties of particles and waves. the Kapitz-Dirac effect demonstrates wave-particle duality by showing that matter waves are diffracted by an incident electromagnetic field as predicted by the wave properties of the particles, i.e., by the diffraction equation nλ = 2dsin(Θ).