Tagged Questions
-2
votes
0answers
28 views
Why is the expectation value of the Hamiltonian/position commutator equal to zero?
I know that the commutator $[H,x]$ is $-i \hbar \,p/m$, but how do I show that the modulus of the expectation value of this is zero?
1
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0answers
79 views
General physics question involving Heisenberg Uncertainty Principle
Question:
An unstable particle produced in a high-energy collision is measured to have an energy of $483\ \mathrm{MeV}$ and an uncertainty in energy of $84\ \mathrm{keV}$. Use the Heisenberg ...
1
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1answer
70 views
Uncertainty Principle and Energy range for an electron in an atom
I have the following exercise:
Use Heisenberg's uncertainty principle and the relation $\Delta u = \sqrt{\langle u^2 \rangle - \langle u \rangle^2}$ to find the range of energy an electron has in an ...
1
vote
1answer
60 views
Why uncertainity is minimum for coherent states?
While reading for quantum damped harmonic oscillator, I came across coherent states, and I asked my prof about them and he said me it is the state at which $\Delta x\Delta y$ is minimum. I didn't ...
0
votes
1answer
341 views
Gaussian wave packet
At our QM intro our professor said that we derive uncertainty principle using the integral of plane waves $\psi = \psi_0(k) e^{i(kx - \omega t)}$ over wave numbers $k$. We do it at $t=0$ hence $\psi = ...
1
vote
2answers
167 views
Showing that position times momentum and energy times time have the same dimensions
I've been asked to show that both the position-momentum uncertainty principle and the energy-time uncertainty principle have the same units.
I've never see a question of this type, so am I allowed to ...
0
votes
1answer
112 views
What's the proper way to approximate the position uncertainty of a particle?
In this problem:
shouldn't $\Delta x\sim\lambda/\sin\theta$ be
$$\Delta x\sim \frac{\lambda}{\sin\theta} - \left(\frac{-\lambda}{\sin\theta}\right) = 2\frac{\lambda}{\sin\theta}$$
instead such ...
2
votes
2answers
1k views
Minimum possible Kinetic Energy of a confined electron
The problem is this:
Consider an electron confined in a region of nuclear
dimensions (about 5 fm). Find its minimum possible
kinetic energy in MeV. Treat this problem as
one-dimensional, and ...
1
vote
1answer
903 views
How does position uncertainty change in time?
I have an online homework for my Modern Physics class, that requires me to find the uncertainty in velocity and position of a duck. The question is as below:
Suppose a duck lives in a universe in ...
0
votes
2answers
2k views
Spectral Line Width and Uncertainty principle
so I've been at this for about 3 - 4 hours now. It is an homework assignment (well part of a question which i've already completed). We did not learn this in class. All work is shown below.
An ...
