Help me please

  • Thread starter jmml
  • Start date
  • #1
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i need to solve 3 problems and i can't because i don' understand this can anyone help me.
sorry for bad english and some bad expressions.
i'm portuguese and i left the school 18 years ago.
now i need some help to begin.
thks a lot


One wave packet wich represent the movement of one free particle in one dimension in unit h=c=1, is given for the expression:

[tex]\Psi[/tex](x,t)= 1/[tex]\sqrt{2\pi}[/tex] [tex]\int-\infty[/tex][tex]\infty[/tex] dk [tex]\varphi(k)[/tex]exp {i(kx-w(k)t)}


where

[tex]\varphi(k)[/tex] = 1/[tex]\sqrt{2\Delta k}[/tex] [tex]\theta[/tex](([tex]\Delta k[/tex])[tex]^{2}[/tex] - (k-[tex]\bar{}k[/tex])[tex]^{2})[/tex] =

1/[tex]\sqrt{2\Delta k}[/tex] , |k-[tex]\bar{}k[/tex] | [tex]\leq[/tex] [tex]\Delta k[/tex]

0 , |k-[tex]\bar{}k[/tex] | > [tex]\Delta k[/tex]

and w(k) = k[tex]^{2}[/tex]/2m


a) show in instant t=0 the wave function is given by:



[tex]\Psi(x,t=0)[/tex]= 1/[tex]\sqrt{\pi\Delta k}[/tex] e[tex]^{i\bar{k}xsin(\Delta k x)}[/tex]/x

and do one graphic of | [tex]\Psi[/tex](x, t=0) |[tex]^{2}[/tex] in function of x


b) do graphicaly [tex]\Delta x[/tex] and [tex]\Delta x[/tex][tex]\Delta k[/tex] and compare result with heisenberg principle of uncertainty.


c) do another graphic of | [tex]\Psi (x,t=1)[/tex] |[tex]^{2}[/tex] and | [tex]\Psi (x,t=2)[/tex] |[tex]^{2}[/tex] in the aproximation.


w(k) = k[tex]^{-}[/tex][tex]^{2}[/tex]/2m + k[tex]^{-}[/tex]/m (k-k[tex]^{-}[/tex])


in function of x and express the conclusion about the speed of the wave packet



d) show that wave packet is solution of the following wave equation.


i [tex]\partial[/tex]/[tex]\partial t[/tex] [tex]\Psi (x,t)[/tex]= -1/2m [tex]\partial[/tex][tex]^{2}[/tex]/[tex]\partial[/tex]x[tex]^{2}[/tex] [tex]\Psi(x,t)[/tex]


e) now with w(k) = [tex]\sqrt{k^{2}+m^{2}}[/tex] Einstein Relation


show the wave packet is solution of the following equation ( equation of Klein and Gordon)

[tex]\partial ^{2}[/tex]/[tex]\partial t^{2}[/tex] [tex]\Psi (x,t)[/tex] = ([tex]\partial ^{2}[/tex]/[tex]\partial x^{2}[/tex] - m[tex]^{2}[/tex]) [tex]\Psi (x,t)[/tex]

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
Gokul43201
Staff Emeritus
Science Advisor
Gold Member
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We need to see some effort from you before we can help. Do you have any thoughts?
 
  • #3
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Unfortunely no

as i said i leave school 18 years ago and now i'm very confused and need help.

if anyone can help i apreciate.

thks
 
  • #4
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anyone can help please
 
  • #5
malawi_glenn
Science Advisor
Homework Helper
4,795
22
what do you need help with? we cant do the whole problem for you. Ask a specific question and we can answer you so you can proceed. WHAT is confusing you?

I mean, many of the things you are supposed to do are jusr basically putting in values in the original expression and see that it works, and show that the wave package fulfil some differential equations.

for example:

a) have you tried to just put in t=0 and to the integration?
 
Last edited:
  • #6
9
0
yes i try that.

but i don't know what happens with [tex]\varphi[/tex](k)
 
  • #7
malawi_glenn
Science Advisor
Homework Helper
4,795
22
okey: first stop mixing LaTeX and usual text, looks very strange..

second; show what you did. Then we can see what you have done wrong, or if you are roght but are not aware of it.
 

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