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Shown in the upper graph is the transcendental equation describing the bound-state energy levels of the Kronig-Penney model. The blue lines represent the maximum of one side of the equation and the red curve represents the other side of the equation. The bottom graph shows the potential energy function: the well width b = 2a = 1 and the well height V = 6.  You may enter the well spacing, D,  using the slider. Restart.  In the animation ħ = 2m = 1.

1. For the allowed changes in potential energy well spacing, describe the band structure.
2. As the well spacing increases, what happens to the band of energies?
3. Explain why this is the case.