How Is the Wavefunction Ψ(x) Derived from Momentum Space?

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Homework Help Overview

The discussion revolves around the derivation of the wavefunction Ψ(x) from momentum space representations in quantum mechanics. Participants are exploring the mathematical relationships between position and momentum representations, particularly focusing on the expressions involving integrals and the definitions of wavefunctions.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants are attempting to understand how the integral expression ∫dp simplifies to ∫dp exp{ipx/h}Ψ(p). There are also inquiries about the notation Ψ(x) being represented as .

Discussion Status

The discussion includes various attempts to clarify the derivation and notation. Some participants express uncertainty about the correctness of the equations and mention potential normalization factors. There is an acknowledgment of differing experiences and understanding levels among participants.

Contextual Notes

Some participants note that the notation may be considered sloppy and highlight discrepancies in the equations presented, such as the use of 'h' versus 'h-bar'. There is also a suggestion that proper equations are necessary for clarity.

Eole
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Here's a derivation of wavefunction of State Ψ in representations of coordinates and momentum
Ψ (x)=<x|Ψ >=<x|∫dp|p><p|Ψ >=∫dp<x|p><p|Ψ>=∫dp exp{ipx/h}Ψ(p)
Ψ (p)=<p|Ψ >=∫dx exp{-ipx/h}Ψ(x)


Ψ (x)=<x|Ψ >=<x|∫dp|p><p|Ψ >=∫dp<x|p><p|Ψ>=∫dp exp{ipx/h}Ψ(p)
i don't understand how ∫dp<x|p><p|Ψ> become ∫dp exp{ipx/h}Ψ(p)
Could you please tell me the drivation of this formula?

and another question is why Ψ (x) could be denoted as <x|Ψ >?
 
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I probably won't be able to help, but I'm sure that if I'm struggling to make sense of that, then other people are too. Some things just can't be written without proper equations. Maybe try writing the equation on Microsoft word's equation tool and attach the document.
 
Eole said:
Here's a derivation of wavefunction of State Ψ in representations of coordinates and momentum
Ψ (x)=<x|Ψ >=<x|∫dp|p><p|Ψ >=∫dp<x|p><p|Ψ>=∫dp exp{ipx/h}Ψ(p)
Ψ (p)=<p|Ψ >=∫dx exp{-ipx/h}Ψ(x)
Ψ (x)=<x|Ψ >=<x|∫dp|p><p|Ψ >=∫dp<x|p><p|Ψ>=∫dp exp{ipx/h}Ψ(p)
i don't understand how ∫dp<x|p><p|Ψ> become ∫dp exp{ipx/h}Ψ(p)
Could you please tell me the drivation of this formula?
and another question is why Ψ (x) could be denoted as <x|Ψ >?

It seems to me that you are asking why
<x|p>=exp{ipx/h}
but surely you must have this derivation in your notes? BTW, the above equation isn't actually quite right (needs a factor in order to normalize it) and, in my notes anyway, the 'h' is actually an 'h-bar'.

As regards your other question, I can only assume that it is very sloppy notation because I have never seen a state use the same symbol as the wave function (although I am still an undergraduate so my experience is rather limited).
 
Eole said:
Ψ (x)=<x|Ψ >=<x|∫dp|p><p|Ψ >=∫dp<x|p><p|Ψ>=∫dp exp{ipx/h}Ψ(p)
i don't understand how ∫dp<x|p><p|Ψ> become ∫dp exp{ipx/h}Ψ(p)
Could you please tell me the drivation of this formula?
and another question is why Ψ (x) could be denoted as <x|Ψ >?

[itex]\psi(x) = \langle x | \psi \rangle[/itex] by definition. It is the component of |x> in the expansion of [itex]| \psi \rangle[/itex] in the position basis.

∫dp<x|p><p|Ψ> = ∫dp exp{ipx/h}Ψ(p), because [itex]\langle x|p \rangle =\exp{ipx/\hbar}[/itex] (apart from a constant factor) and <p|Ψ>=Ψ(p), again by definition.
 

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