Questions tagged [mean-free-path]

The average length that a molecule will travel in a fluid before colliding with another molecule.

26 questions
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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 ...
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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 ...
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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}{\...
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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 ...
309 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 ...
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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 ...
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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 ...
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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 ...
525 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 ...
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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 ...
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Ion charge exchange mean free path

I am using the following equation to calculate the mean free path between a deuteron ion and background gas: $$\lambda_{d-gas} = \frac{kT_{gas}}{p_{gas} \, \sigma_{10}}$$ Where $\sigma_{10}$ is the ...
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Energy of particle in electric field

I'm taking a physics class and the professor teaches us really basic things in lecture and then gives homework way beyond what he taught in lecture. Obviously I need to find some resource other than ...
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Do particles in the solar core travel at the same speed as they would in vacuum?

I just read the Wikipedia article on the Sun. The section on Solar Core states It has a density of up to 150 g/cm3 (about 150 times the density of water) Do the particles (atomic, and sub-...
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The number of mean free paths which a particle traverses is independent of the material traversed

This is a manual from a Monte Carlo physics manual: Computing the occurrence of a process Can anyone tell me why the number of mean free paths of a particle is independent of the material which it ...