Questions tagged [mean-free-path]
The average length that a molecule will travel in a fluid before colliding with another molecule.
61
questions
1
vote
1
answer
3k
views
Mean free path of electron in air?
I'm interested in approximating the mean free path of an electron in air. I think I'm going to need to add something more into my approximation because currently I calculate $400m$ for the mean free ...
- 713
1
vote
1
answer
91
views
Two versions of Diffusion coefficient
I found two versions of the Diffusion coefficient, first:
$$D=\frac{\pi \lambda }{8}\overline{c}$$
Where $ \overline{c}$ ist the particles mean thermal velocity and $\lambda$ the particles mean free ...
4
votes
2
answers
190
views
Usually, how much does a phonon travel without scattering?
Phonons propagate without problems in a lattice, until they scatter on something, like a defect, an electron, or another phonon. But in a typical solid at room temperature, how much (or how long) is ...
- 97
1
vote
0
answers
55
views
Mean free path for charged molecule inside air
Question
I would like to compute the mean free path ($\lambda$) for a "heavy" charged molecule ($M$amu, $q$ charge) in a low pressure gaz (air, but also ions such as Ca$^+$). I think I figured out ...
- 31
1
vote
1
answer
695
views
The mean free path of electrons in high vacuum is 26 billion kilometres?
I used this formula to calculate the mean free path length of an electron in high vacuum.
$$\lambda = \frac{k T}{\sqrt{2}\cdot4\pi r^2 \cdot p}$$
where k is the Boltzmann konstant, T the temperature ...
- 113
2
votes
1
answer
2k
views
How to (hypothetically) calculate $\tau$, the mean free time?
Referring to the Drude Model, I've seen a lot of excellent questions on whether $\tau$ should be thought of as the "average time between collisions" or the "average time until the next collision", and ...
- 3,075
0
votes
0
answers
507
views
Electron mean free path as a function of pressure
How do I calculate electron beam mean free path as a function of vacuum pressure? For example, if I am pumping a vacuum system down and have an electron beam of known energy, what is the mean free ...
19
votes
3
answers
3k
views
Rigorous derivation of the mean free path in a gas
Can anyone supply me with a derivation of the mean free path, of
particles in a Maxwell Boltzmann Gas?
Cited in various literature is the formula,
\begin{align}
\begin{split}
\ell&=\frac{1}{\...
- 579
1
vote
0
answers
87
views
Mean free path for $3\rightarrow 1$ scattering
I want to calculate the mean free path of an antineutrino in nuclear matter where it can undergo the reaction $p+e^-+\bar{\nu} \rightarrow n$, which I imagine will involve calculating the rate of that ...
- 935
1
vote
2
answers
1k
views
Most probable free path length
The distribution of scattering time is
$nv\sigma e^{-nv\sigma t}$
where $\sigma$ is the collision-cross section, $n$ is the number density of molecules and $v$ is the average relative velocity. This ...
- 155
1
vote
2
answers
84
views
How is the waveform deviation from the equilibrium related to the air molecule movement?
I'm not sure if this is a stupid question. I've been considering the deviation from the equilibrium reflects the air pressure, with larger deviations reflecting higher air pressure. But in Reetz and ...
- 19
0
votes
0
answers
136
views
Average distance travelled before absorbtion 253 nm photon in air
At first I wanted to use term "Mean free path" in title but I know it means other kinds of interactions too,not just absorbtion.What I really mean is mean free path but only for absorbtion.
For ...
- 734
0
votes
1
answer
102
views
How to interpret 'electron energy above fermi level (eV)'?
In some mean free path graphs, I see 'electron energy above Fermi level (eV)' on the x-axis See figure: What does it mean? Is it electrons kinetic energy in the material?
What happens if the graph ...
- 51
1
vote
2
answers
3k
views
Mean free path of gas mixture
I come cross a question about calculate the MFP of a gas mixture, which contains several different kinds of molecules, each has different size, velocity and number density. My question is: How can I ...
- 137
0
votes
2
answers
152
views
Is penetration of a fast particle deep into a medium a quantum mechanical effect?
Consider the cosmic rays. The muons can travel 15000 meters through the atmosphere and get down to sea level. If this is not a quantum mechanical effect, its penetration depth is determined by the ...
- 4,122