12.07.2015 Views

Simple Nature - Light and Matter

Simple Nature - Light and Matter

Simple Nature - Light and Matter

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C The figure shows a skateboarder tipping over into a swimmingpool with zero initial kinetic energy. There is no friction, the corners aresmooth enough to allow the skater to pass over the smoothly, <strong>and</strong> thevertical distances are small enough so that negligible time is required forthe vertical parts of the motion. The pool is divided into a deep end <strong>and</strong> ashallow end. Their widths are equal. The deep end is four times deeper.(1) Classically, compare the skater’s velocity in the left <strong>and</strong> right regions,<strong>and</strong> infer the probability of finding the skater in either of the two halves ifan observer peeks at a r<strong>and</strong>om moment. (2) Quantum-mechanically, thiscould be a one-dimensional model of an electron shared between twoatoms in a diatomic molecule. Compare the electron’s kinetic energies,momenta, <strong>and</strong> wavelengths in the two sides. For simplicity, let’s assumethat there is no tunneling into the classically forbidden regions. What isthe simplest st<strong>and</strong>ing-wave pattern that you can draw, <strong>and</strong> what are theprobabilities of finding the electron in one side or the other? Does thisobey the correspondence principle?876 Chapter 13 Quantum Physics

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