# Questions tagged [dispersion]

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

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### Why varying the frequency of a propagation wave in a non-dispersive media doesn’t change it’s propagation velocity?

Why varying the frequency of a propagation wave in a non-dispersive media doesn’t change it’s propagation velocity? Before anything, I want to note that I’ve seen already similar questions on this ...
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### Dispersion Relation and Eigenvectors of SSH Model in Tight Binding

Consider a one-dimensional chain of atoms as shown in the figure. Let the spacing between the atoms be $a$. Assume that the onsite energy is the same at each point and is equal to $0$ (without any ...
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### What is the $E$-$k$ relation of electron in valence band?

What is the $E$-$k$ relation of electron in valence band? $E$-$k$ relation for electron in conduction band is known but how to calculate energy of electron in valence band?
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### What is meant by a dispersion relation when complex integration in the Cutkosky rules' derivation or the computation of form factors $F(q^2)$ is used?

In the context of calculations of loop diagrams with Cutkosky-rules very often the concept of dispersion relation is mentioned. For instance this technique is used in Vol. 4 of Landau-Lifshitz for the ...
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### Why does light not disperse in air?

I was studying the prism and how and why it disperses light. My teacher told me that in a prism different wavelengths of light have different refractive indexes because the refractive index depends ...
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### $E$-$k$ diagram under an applied Electric Field

We know from solid-state physics, if an electric field is applied, the band bends in the band diagram. How does this change the $E$-$k$ diagram?
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### What happens to the optical branch solution in the limit of same masses in a diatomic chain?

For a monoatomic chain, we get the following dispersion relation: $\omega(k) = \sqrt{\frac{4 \kappa}{m}\sin^2{\left(\frac{ka}{2}\right)}}$, where $m$ is the atom mass, $\kappa$ is the spring constant, ...
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### Why does Cauchy's equation for refractive index contain only even power terms?

Cauchy's equation is an empirical relation that defines the refractive index of a material in terms of wavelength: $$n(\lambda) = A + \frac{B}{\lambda^2} + \frac{C}{\lambda^4} + ...$$ While I ...
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### One-dimensional diatomic chain phases

In my solid state book, when deriving the dispersion relation of a diatomic one-dimensional chain, the author makes the following Ansatz for the oscillation of the first (x) and seond (y) atom in the ...
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### How to interpret dispersion curves?

I have trouble understanding the dispersion curves, especially the x-axis. As i understand it, the x-axis is the wave-vector k. Which would mean that waves of different wavelengths, move at different ...
The electromagnetic spectrum's wavelengths all travel at the same speed, $c$. Also, the wavelength $\lambda$ and frequency $\nu$ are related by $c = \lambda \cdot \nu$. Since all moving particles here ...