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Dispersion refers to the frequency dependence of the properties of a wave.

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Why do some types of waves disperse?

Two Types of Dispsersion There are two ways to think about dispersion, spatial and temporal. … The longer the memory of these previous currents, the stronger the temporal dispersion. …
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Why do water waves with longer wavelengths travel faster?

Definitions deep water limit : when the wavelength of the mode/wave is much less than the depth of the water shallow water limit : when the wavelength of the mode/wave is much larger than the wate …
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2 votes
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Smallest relative velocity driving a two-stream instability

Thus, the dispersion relation goes to: $$ D\left( \omega \right) = 1 - \left( \frac{ \omega_{pi} }{ \omega } \right)^{2} - \left( \frac{ \omega_{pe} }{ \left( \omega - \mathbf{k} \cdot \mathbf{V}_{o} \ …
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Dispersion relation for electron plasma waves at large and small wavelengths

First, keep the derivative in terms of the wavenumber, $k$, and the thermal speed, $v_{th}$ to see that the group speed is given by: $$ \frac{ \partial \omega }{ \partial k } = \frac{ 3 \ k \ v_{th}^{ …
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4 votes

Derviation of group velocity

Let us assume that a dispersion relation, $\omega$ $=$ $\mathcal{W}\left( \boldsymbol{\kappa}, \textbf{x}, t \right)$, exists and may be solved for positive real roots. … In general, there will be multiple solutions to the dispersion relation, where each solution is referred to as different modes. …
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0 votes

Physical significance of growth rate in plasma

The top panel shows the real part of the frequency, $\omega_{r}$, and the bottom the imaginary part, $\gamma$, versus the projection of the wave vector orthogonal to the quasi-static magnetic field, $ …
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1 vote

Nonsensical dispersion relations for elastic wave propagation

In the above, there is one propagation mode (in blue) which extends out to infinite radius in k-space, which seems to physically makes no sense, since $\omega$ is fixed, so you'd expect the dispersion … So this is probably a simple question, but is there any type of material which can have this sort of dispersion relation, or is there some reason why real materials can never behave in this manner (ie, …
honeste_vivere's user avatar
1 vote

Understanding group velocity

The following is taken from the intro to this question: https://physics.stackexchange.com/a/381974/59023 Background Let us define some relevant parameters: Wave Number $\equiv$ $\mathbf{k} = \mathbf{ …
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0 votes

What happens to Langmuir waves at a density gradient in plasmas?

I tried to derive the dispersion relation by linearising the electron momentum and continuity equations and Gauss' law, but very quickly ran into something that could not be converted into a dispersion … If you are specifically curious about a Langmuir wave running into a density gradient, look at the Krafft et al. [2014] paper for a proper dispersion relation. …
honeste_vivere's user avatar
3 votes

Linear vs. quadratic dispersion relation

For instance, a whistler mode wave can have a cubic dispersion relation at low frequencies. In this limit, the higher(smaller) frequencies(wavelengths) propagate faster than the converse. …
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Non-linear waves and shock formation

Dispersion effects, on the other hand, do not affect reversibility and increase the order of the derivatives in the equations by an even number. … Interestingly, dispersion is not an irreversible term because it increases the order of the derivatives in the equations by an even number. …
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