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Unformatted text preview: Ben Sauerwine Practice for Qualifying Exams Problem Source: CMU August 2004 Qualifying Exam (a) Solve the energy eigenvalue equation for a particle of mass m in the square well potential that vanishes for 0 < x < a and equals ( ) x V ∞ + elsewhere. Show that the energy eigenvalues are given by: ,... 3 , 2 , 1 , 2 2 2 2 2 = = n ma n E n π h with the corresponding normalized energy eigenfunctions ( ) ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = a x n a x n π ψ sin 2 Explicitly discuss the boundary conditions. The boundary conditions are: ( ) ( ) ( ) ( ) ( ) x E x x V x m a ψ ψ ψ ψ = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ + ∂ ∂ − = = 2 2 2 2 h Here boundary conditions on the derivative are waived in the case of an infinitepotential barrier. Showing that these solutions are valid by substitution, I take: ( ) ( ) x E a x n a ma n a x n a n a m a x n a x m x H n n n ψ π π π π π ψ = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ∂ ∂ − = sin 2 2 sin 2 2 sin 2 2 2 2 2 2 2 2 2 2 2 h h h Showing that these solutions are normal by substitution, I take ( ) normalized a a boundary a x n n a a a dx a x n a dx a x n a dx x a a a n = = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ → → ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = ∫ ∫ ∫ 1 2 1 2 2 sin 2 2 1 2 1 2 2 cos 2 1 2 1 2 sin 2 2 2 π π π π ψ (b) Suppose we place two electrons (spin ½) in the infinite square well potential above. Determine the twoparticle wave function, whose spatial part is ( 2 1 , , 2 1 x x n n ) ψ for the ground state(s) and the first excited state(s), neglecting...
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This note was uploaded on 04/07/2012 for the course PHYSICS 767 taught by Professor Dr.jaouni during the Spring '12 term at Abu Dhabi University.
 Spring '12
 Dr.Jaouni
 Energy, Mass

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