Recent content by renec112

Oh right.. I think i misunderstood the question then. I need to find ##< x(t)> ## for all later times. But i can't see, how i can find that.. You are saying ##\frac{d<x>}{dt} \neq < x(t)> ## I am not sure why i should fine ##< x >## I can see it's a part of the equation, but why does it give...

Thanks for helping me :) Its ##p = mv## off course. Oh i so the m' cancels and i am left with only ##<x>##... Nice trick ! Thank you :)

## v = \frac{1}{2} m v^2## ## = \frac{m^2v^2}{2m}## ## = \frac{p^2}{2m}## ## \Rightarrow p = \sqrt{2 v m}## Like this?

Oh I see. That's very smart. This is what i did: ##\frac{d<x>}{dt} = \frac{i}{\hbar} <[H,x]>## insert hamilton ##= \frac{i}{\hbar} <[P^2/2m,x]>## ##= \frac{i}{2 m \hbar } <[PP,x]>## ##= \frac{i}{2 m \hbar } <P[P,x]+[P,x]P>## ##= \frac{i}{2 m \hbar } <-P[x,P]-[x,P]P>## ##= \frac{i}{2 m \hbar }...

Actually when you say it like that.. I guess i thought in ## H = \frac{p^2}{2m} = \frac{\hbar}{2m}\frac{\partial^2}{\partial x^2}## the ##p## is just a constant but off course it's an operator: ##p = i \hbar \frac{\partial}{\partial x}## I guess the only thing to do is to differentiate a couple...

Hello physics forums. I'm trying to solve an old exam question. Would love your help. Homework Statement A free particle in one dimension is described by: ## H = \frac{p^2}{2m} = \frac{\hbar}{2m}\frac{\partial^2}{\partial x^2}## at ##t = 0## The wavefunction is described by: ## \Psi(x,0) =...

Okay i think i understand so we are calculating: ##\sigma_x \sigma_{L_x} \geq |\frac{1}{2i} <[x,L_x]>| ## and not: ##\sigma_x \sigma_{L_z} \geq |\frac{1}{2i} <[x,L_z]>| ##? Thank you for helping me.

Me and my group had a laugh at this, we are just finished doing it and it was very nasty indeed :D Thank you very much for the comment. - You mean ## <\sigma_{L_z}^2> ## and not ## <\sigma_{L_x}^2> ## Right? We have actually calculated ##<L_z## and ##<L_z^2>## from another task. We did it...

Hi physics forms! I'm practicing to for an Quantum mechanics exam, and i have a problem. 1. Homework Statement I have two problems, but it's all related to the same main task. I have a state for the Hydrogen: ## \Psi = \frac{1}{\sqrt{2}}(\psi_{100} + i \psi_{211})## where ## \psi_{nlm}##...

Off course! Thanks for being so patient with me. Now it works out :)

Right, so i have: ## = \sqrt{\frac{b}{2 \pi}} (\frac{1}{-ip/\hbar + b} - \frac{1}{-ip/\hbar - b}) ## Guess there's not much to do - you think taking the norm squared here is a reasonable idea? Thanks for helping me out.

Okay this is embarrassing. It was suppose to be a ##\hbar##, but when i wrote from my notes to latex i thought it was a ##t##

Thanks for the reply! Oh off course not.. My blunder.. t is time - are you thinking about finding an expression for t and substituting it?

Thanks! I just had a look and i see it should be: ## = \sqrt{\frac{b}{2 \pi}} (\frac{1}{-ip/t + b} - \frac{1}{-ip/t - b}) ## Giving me ## = \sqrt{\frac{b}{2 \pi}} (\frac{1}{-ip/t} + \frac{1}{-ip/t } + \frac{1 }{b}-\frac{1}{b}) ## ## = \sqrt{\frac{b}{2 \pi}} (-2\frac{1}{-ip/t} ) ## ## = -2...

Homework Statement A particle with mass m is moving on the x-axis and is described by ## \psi_b = \sqrt{b} \cdot e^{-b |x|}## Find the probability distribution for the particles momentum Homework Equations ## \Phi (p)= \frac{1}{\sqrt{2 \pi}} \int_{-\infty}^\infty \Psi(x,0) \cdot e^{-ipx} dx##...