# 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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### Do photons slow down this much in the Sun's gravitational field?

I just heard someone mention that photons take 40 thousand years to travel from the centre of the Sun to its surface which is roughly 700,000 kilometres. How is that possible if the speed of light/...
13 views

### The question is about kinetic theory of gases regarding mean free path

In the derivation we have stated that the molecule moves only in a particular cylinder ( due to assumption that molecules of gas’s travel in straight line ) and travels through the cylinder even after ...
49 views

### How to calculate the mean free time in Drude model?

According to Drude model, the average electron takes some time to go from one ion to another: this time is called mean free time. The problem is there isn't a satisfactory definition of this mean free ...
32 views

### Why does thermal conductivity decrease from solids to gases?

I am learning in my heat transfer class that the thermal conductivity decreases from solids to liquids to gases i.e. $$K_{solid} > K_{liquid}>K_{gas}$$ The reason cited is that (based on my ...
109 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 ...
25 views

569 views

### 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 ...
676 views

### Mean free path in 2d?

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 ...
181 views

### Derivation of relativistic mean free path

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 ...
53 views

### How photons get distributed in a system?

Let's say I'm in a room, and there are plenty of things in my room like carpet,mirrors,glass and other stuff.And I see there are shadow regions and fully bright regions, and I want to know how photons ...
103 views

### Mean free path in spherical coordinate

I am thinking about a distribution with spatially inhomogeneous cross section in spherical coordinate. Starting with 1-dimensional case, a change of the flux passing through a slab with length $dx$ is ...
388 views

### Does it make sense to define the mean free path in quantum mechanics?

The mean free path defined in classical molecule dynamics has a strong classical flavor. Is it sensible to generalize the idea to quantum mechanics?
630 views

### Copper mean free path dependence on temperature

I'm doing simulations of copper, where the temperature can reach up to ~1300 K. Some calculations depend on the mean free path (MFP) of copper. The only value I've found for it is 39nm and it's ...
5k views

### RMS Free Path vs Mean Free Path

I am trying to determine the mathematical difference between mean free path and root-mean-square free path. For an ideal gas, the relaxation time is $$\tau=\frac{1}{\sqrt2 \pi nd^2 \bar v}$$ and the ...
962 views

### Molecular mean free path probability

Let's let $p(\xi)$ be the probability a molecule travels at least $\xi$ between collisions, lets say $\xi=0.01$. When I think of this statement, I think it it is the probability the molecule is able ...
680 views

### 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 ...
111 views

### 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-...
150 views

### 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 ...