- #1
CAF123
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Homework Statement
In my physics course, we have been given 'plausibility' arguments for the solutions of the time dependent/time independent SE. However, have done a Calculus course alongside, I feel I should really derive these solutions, since I have learned about the techniques of second order diff eqns.
The Attempt at a Solution
Considering the simple case first: ##V = 0##. In such a region, the TISE reduces to $$\frac{-\hbar^2}{2m} \frac{d^2}{dx^2} \psi(x) - E\psi(x) = 0.$$ Take the auxiliary eqn of this to get ##-\frac{\hbar^2}{2m}r^2 - E = 0 => r = ±\frac{\sqrt{2mE}}{\hbar}i## and so the general solution is $$\psi(x) = A\cos(\frac{\sqrt{2mE}}{\hbar}) + B\sin(\frac{\sqrt{2mE}}{\hbar})$$
First question:I recognise my expression for ##r## as the expression for ##k##, the wavenumber. Can I simply let ##r = k## to recover this expression? If so, why?
Second question:I know the general soln in this case is ##\psi(x) = Ae^{ikx} + Be^{-ikx}. ##How does this follow from what I have? I thought about using the method of reduction of order to perhaps find this other term but then I noticed that the expression that I got did not have a term ##i\sin##, so what I have does not conform with the answer anyway.
Many thanks.