# Pulse of alpha particles

1. Nov 14, 2008

### najima

1. The problem statement, all variables and given/known data

a pulse 1 m long contains 1000 α particles.at t=0,each α particles in the state

ψ(x,0){1/10e^(-ik_0 ) lxl≤50cm,k_0=π/50 and 0 for elsewhere,}
at t=0 ,how many particle s have momentume in the interval 0<hk<hk_0?
2. Relevant equations
introduction to quantum mechanics by liboff chapter 5/problems 4

3. The attempt at a solutionI dont understand what does it mean!! I think I have to calculate expectation value?am I right?

2. Nov 14, 2008

### HallsofIvy

Staff Emeritus
Re: prob.

Expectation value of what? You are asked for the number of particles within a certain range of momenta. Since you know there are 1000 particles it would be sufficient to determine the percentage within that range. Looks to me like you want to calculate the probabilty a given partical has that momentum.

3. Nov 14, 2008

### najima

Re: prob.

I cant get the answer ,plz, help more.:-(

4. Nov 14, 2008

### najima

Re: prob.

oh !finally I got! thax man!!