Questions tagged [mean-free-path]

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

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Mean free path equation for plasma

Does the mean free path equation $$\lambda=\frac{1}{\sqrt{2}\pi d^2 n_v}$$ work for collisions in plasma or just for gas?
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Predicting electrical mean free path in nanostructures?

How does one roughly predict the mean free path for electrical conduction in a nanostructure at different temperatures and under different electrical conditions such as different voltages and ...
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Standard deviation for a free path distribution

I would like to be able to describe a particles path before collisions with greater precision. We can calculate the "mean" free path of a particle before colliding moving particles, but I ...
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How is number of collisions per unit distance related to mean free path?

Recently I have been studying Kinetic Theory Of Gases, with one of the topics as collision frequency. I know that collision frequency is inverse of relaxation time which is also the measure of number ...
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Determining the single particle energies in a neutrino opacity calculation

I'm attempting to recreate some plots from this paper on neutrino opacity calculations for interacting matter at supra-nuclear densities. Namely, I'm trying to write a Python script to perform the ...
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Why does computing mean free path from an air molecule's reference frame seem to greatly overestimate path length?

I was interested in seeing if I could derive the mean free path of an "air molecule" by considering the reference frame of an individual molecule as other particles moved around it randomly. ...
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Number of fog droplets in the air

I have an issue with the official solution to this problem from BelPhO: Visibility on the road is 100 m. Assuming that the diameter of a fog droplet is 1 micron, estimate the concentration of fog ...
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Mean free path of molecules

So in the book concepts in thermal physics(by Stephan and Katherine Blundell) the expression of mean scattering time is derived as shown(please refer the book for more). If we replace vdt in the ...
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Why is the sphere of influence of the molecule in mean free path a cylinder?

In my book for deriving mean free path a cylinder is taken to act as a sphere of influence of molecules with which it could bump into other molecules and its radius = diameter of the molecule we are ...
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How does $\frac{\langle v\rangle}{\langle v_r\rangle}=\frac{1}{\sqrt2}$ imply the formula for the mean free path?

In this question, it was asked how the formula $$l=\frac{1}{\sqrt 2n\sigma }$$ can be rigorously derived for a Maxwell-Boltzmann gas. Here $l$ is the mean free path length in a gas, $n$ is the gas ...
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Free Path Probability Distribution for an Ideal Gas

Suppose we have a gas with collisions. The mean free path, $l$, is the average distance a particle travels before colliding with another particle. This is the average, but what is the probability ...
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1 vote
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Question regarding correction factor in Mean free path

1)The expression for $Mean$ $Free$ $Path$ (ie) , $$λ=\dfrac{1}{πd²\dfrac{n}{V}}$$ is derived under the assumption that the particles except the one( let's consider it as particle $A$) you're ...
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Collisional cross-section from attenuation factor

I am trying to find the mean free path of silver atoms travelling through air (I am given the temperature, pressure and that they are attenuated by a factor $2.72$ in a distance of $10^{-2}$m). I know ...
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Mean free path regarding billiards

Is there a generalization of the mean free path for macro-objects such as the distance the white billiard ball could travel before hitting an other billiard ball?
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Ratio of mean free paths between two equal volumes at different temperature, separated by a partition with pinhole

Question: A container is divided into two equal parts I and II by a partition with a small hole of diameter $d$. The two partitions are filled with same ideal gas, but held at temperatures $T_I$​= ...
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What does ultra-rarefied gas mean?

Without using any math, can you explain to me what a rarefied gas is? And then what an ultra-rarefied gas is? I'd like to understand it from a conceptual level if you can make connections to other ...
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Which average are we taking in a rigorous calculation of the mean free path in a gas?

This is a question at one level beyond the standard introductions to kinetic theory. I want to know which average we are taking when we talk about a mean free path in a gas. I recently read Steve T. ...
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1 vote
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Why is mean free path independent of mass?

In this page of Hyperphysics, I am puzzled as to why there isn't any mass dependence in the expressions for mean free path. Here are the two equations as mentioned in the website: When only one ...
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Why is the mean free path length of an electron in a solid described by a "universal curve"? (doesn't include electron density)

I've been experimenting with XPS (X-ray photoelectron spectroscopy) and learned that the depth from which the observed electrons originated depends on their mean free path length, which makes sense to ...
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How to calculate the free mean path of electrons in the gas mixture? [closed]

How to calculate the free mean path of electrons in the gas mixture? I understand (a little bit) the mean free path concept for the atomic collisions but I am not sure what to do if I am interested in ...
486 views

What is the mean free path (MFP) of a Cosmic microwave background radiation (CMBR) photon?

If the IGM (inter-galactic medium) had a massive particle (proton) every cubic metre, or a carbon grain every cubic kilometre, what would be the MFP of a CMBR photon? The coherence length of the ...
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How can mean free path affect the propagation of sound in a gas?

I was thinking, since mean free path is a measure of "how long" a particle has to travel to collide with another, that this surely must influence sound propagation somehow. I would say this ...
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What does this equation represent?

While doing the Franck-Hertz experiment I noticed that I have been asked to write the current as a function of the Mean Free Path as following: $$I=a\cdot e^{-\frac{b}{\lambda}}$$ I- current $\lambda$...
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Franck Hertz experiment and the Mean Free Path

As part of my project in physics, I tried to repeat the franck hertz experiment, I did the same experiment with Neon and Mercury (the lengh between the catode and lattice is $5 mm$), I measured the ...
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Infering the mean distance from density

A simple calculation surely but how we can infer the mean distance $l_{\text{mean}}$ between particles from their density $n$, i.e : $$l_{\text{mean}}=\left(\dfrac{1}{n}\right)^{1/3}$$ ? I tried to ...
1 vote
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Monte Carlo approach to determining mean free path of Lévy dust

Problem statement I am trying to determine the mean free path $\lambda$ of a so-called Lévy dust, i.e. $M$ points in a square $L\times L$ environment with distances between subsequent points ...
1 vote
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speed distribution and mean free path of gases at pressure

I know that at 18,000 ft. above mean sea level, the atm. pressure ~half of what it is at seal level (760 Torr). The temperature also decreases by 70C. a. How would this change the speed distribution ...
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Let us say we have a collection of $n$ stationary balls per square meter each of diameter $d$ and we roll an identical ball between them. Then what is the free mean path of this ball? My ...
I am working through a short derivation found in Abramowicz 1991 regarding the mean free path of a photon. We have a fluid moving in a particular direction with velocity $v$ and in an inertial rest ...