Quantum Physics For Dummies
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In quantum physics, you can apply the radial equation outside a square well (where the radius is greater than a). In the region r > a, the particle is just like a free particle, so here's what the radial equation looks like:


You solve this equation as follows:


you substitute


so that Rnl(r) becomes


Using this substitution means that the radial equation takes the following form:


The solution is a combination of spherical Bessel functions and spherical Neumann functions, where Bl is a constant:


If the energy E < 0, you must have Cl = i Bl", so that the wave function decays exponentially at large distances r. So the radial solution outside the square well looks like this, where


Given that the wave function inside the square well is


So how do you find the constants Al and Bl? You find those constants through continuity constraints: At the inside/outside boundary, where r = a, the wave function and its first derivative must be continuous. So to determine Al and Bl, you have to solve these two equations:


About This Article

This article is from the book:

About the book author:

Steven Holzner is an award-winning author of technical and science books (like Physics For Dummies and Differential Equations For Dummies). He graduated from MIT and did his PhD in physics at Cornell University, where he was on the teaching faculty for 10 years. He’s also been on the faculty of MIT. Steve also teaches corporate groups around the country.

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