A question about Dirac Delta Potential Well solution

Positron137
Messages
41
Reaction score
0
In Griffith's Introduction to Quantum Mechanics, on page 56, he says that for scattering states
(E > 0), the general solution for the Dirac delta potential function V(x) = -aδ(x) (once plugged into the Schrodinger Equation), is the following: ψ(x) = Ae^(ikx) + Be^(-ikx), where k = (√2mE)/h. After that, he states that in the general solution for ψ(x) (stated above), both terms do NOT blow up in the section of the well where x < 0. But this doesn't make sense, because earlier, when he was demonstrating bound states (E < 0) , he stated that the second term, Be^(-ikx), blows up at infinity when x < 0. But here, for scattering states, he states that NEITHER term blows up as x < 0, which seems contradictory. Could anyone explain why this is true (why neither term blows up for a scattering state, when x < 0)? Thanks!
 
Physics news on Phys.org
The difference, I believe is in the "i" (of the beholder BWAAHAHAHA). But seriously. The scattering states have an i, thus are oscillatory, and the bound states don't have an i, and hence are 'regular' exponentials, which blow up at one of the infinities (+ or -).
 
Ah ok. Thanks! LOL I was getting confused. So the reason why it doesn't "blow up" as we would expect it to is because for complex exponentials, as x -> infinity, e^(ikx) and e^(-ikx) don't blow up? Actually, that kinda makes sense because e^ix is like going in a circle in the complex plane. Thanks for the clarification!
 
It's funny you ask this, I asked the exact same question and didn't get a good explanation; I don't think my instructor understood my question. I actually still have the equation circled in my textbook with a "why" written next to it. This does clarify it though, it's pretty obvious now that I think of it... I didn't notice the distinction... thanks for posting.
 
No problem! LOL yeah, I was also confused - why for bound states, one of the terms blew up, and why for the scattering states, both e^(ikx) AND e^(-ikx) terms were kept, even though x tended to negative infinity.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In her YouTube video Bell’s Theorem Experiments on Entangled Photons, Dr. Fugate shows how polarization-entangled photons violate Bell’s inequality. In this Insight, I will use quantum information theory to explain why such entangled photon-polarization qubits violate the version of Bell’s inequality due to John Clauser, Michael Horne, Abner Shimony, and Richard Holt known as the...
Not an expert in QM. AFAIK, Schrödinger's equation is quite different from the classical wave equation. The former is an equation for the dynamics of the state of a (quantum?) system, the latter is an equation for the dynamics of a (classical) degree of freedom. As a matter of fact, Schrödinger's equation is first order in time derivatives, while the classical wave equation is second order. But, AFAIK, Schrödinger's equation is a wave equation; only its interpretation makes it non-classical...
I asked a question related to a table levitating but I am going to try to be specific about my question after one of the forum mentors stated I should make my question more specific (although I'm still not sure why one couldn't have asked if a table levitating is possible according to physics). Specifically, I am interested in knowing how much justification we have for an extreme low probability thermal fluctuation that results in a "miraculous" event compared to, say, a dice roll. Does a...

Similar threads

Back
Top