# Questions tagged [diffusion]

Diffusion is the net movement (spreading out) of molecules or atoms down a concentration gradient: from a region of high concentration to a region of low concentration.

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### Diffusion due to difference in partial pressure

I learnt about diffusion as the flow of component from a region of higher concentration to lower concentration. Fine, I understood this because for example , if we spray a perfume at one corner of an ...
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### Diffusion time with a variable mean free path

If I have a population of particles diffusing outwards with mean free path $\lambda$, the time taken for them to reach an average displacement $R$ from the centre is $$ct = \frac{R^2}{\lambda},$$ ...
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### Similarity in the solution for diffusion and Schrödinger equations [duplicate]

Both diffusion and Schrödinger equations are PDEs (first order in time and second order in space) with a different physical meaning. When solving a simple case of 1d diffusion with fixed boundary ...
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### Intuition re. log scale versus linear scale

I have a dataset with the speed of movement of two sets of particles (the red, slower, and the blue, faster) as calculated by the diffusion constant. Below is a histogram, on the left on linear scale ...
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### Is 1D diffusion equivalent to diffusion in symmetrical coordinates?

Say you are modelling heat diffusion from hot air into a sphere. The thermal conductivity is the same at all positions on the sphere. Using the 1D diffusion equation, the temperature of the sphere is ...
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### How to derive Fick's law of diffusion from kinetic theory?

I'm studying diffusion limits of kinetic equations and trying to figure out how one may (at least formally) derive Fick's law of diffusion (and hence the diffusion equation), i.e. \begin{align} \nabla\...
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### Cases for reasoning about mass transfer

I'm doing some simulations of a 1D system with diffusion. One boundary has a no-flux boundary condition, while the other boundary has a prescribed-flux boundary condition with a specified mass ...
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### Why doesn't the Diffusion Equation with an initial condition of $u = x$ lead to an even distribution?

Diffusion equation, or Fick's second law states $$\frac{\partial u}{\partial t} = D\frac{\partial^2 u}{\partial^2 x}$$ where $u$ is the concentration of the molecules. My question is, say if we have ...
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### Why are linear diffusion graphs limited to a max and min value. Graph shown in link

This is the graph https://prnt.sc/vpwcz6 I have tried various things to understand why the limits are the way they are for the specific metals. I tried to check if the limit is their melting point but ...
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### How can I use the Navier-Stokes equation to model the diffusion of a gas with the data I gathered?

I am currently a senior high school student taking IB and I chose to write an extended essay in physics. The essay is about the diffusion of a gas with the research questions: "How does the ...
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### Does membrane permeability affect the equilibrium reached by two different concentrations of equally charged ions?

I'm asking this question to aid understanding of the formation of membrane potential in a cell from electrochemical gradients of ions e.g. why the membrane potential is skewed towards the equilibrium ...
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