# Tag Info

Accepted

### Are QED Feynman diagrams readable in any order?

Cooking recipe: Diagram (a): Start with the outgoing electron (i.e. the electron in the final state with momentum $p^\prime$): $\, \bar{u}(p^\prime)$ Following the electron line backwards (i.e. ...
• 4,631

### Complex Refractive Indices, Absorption, and Transparency

A wave propagating in a uniform medum in the $+z$ direction can be expressed as (the real part of) $$E = E_0e^{i(\omega t - nk_0 z)}$$ where $\omega$ is the angular frequency, $k_0 = 2\pi/\lambda$ is ...
• 13.5k

### What makes electron scattering more useful than alpha particle scattering for resolving the structure of the nucleus?

Electron scattering is more useful than alpha scattering for at least a couple of reasons: The electron is a point particle so its de Broglie wavelength ($\lambda=h/p$) and hence resolution is just ...
• 10.9k
1 vote

### What causes light to scatter in a medium?

One important element about crystalline structures is what they represent: On a bigger picture, the crystal structure tells you, among other things, what the different bands in a material look like, ...
• 825
1 vote

### Scattering, Perturbation and asymptotic states in LSZ reduction formula

When I first faced the issue of in-out asymptotic states reading Bjorken-Drell I've had your same doubt 2) and I've worked out some details trying to disentangle it. Before writing them down, I should ...
• 59
1 vote

### Repulsive force between electrons at relativistic speeds

The Lorentz force law is already a fully relativistic equation and Lorentz covariant, which is not too surprising when you consider the Lorentz transformations of special relativity are named after ...
• 2,040
1 vote
Accepted

### Calculation of illumination from the Sun and sky - explanation needed

Please transcribe or paraphrase enough of the surrounding text so that this question can be intelligible without reference to a third-party link and add it to your question. "IO" is just $10$...
• 13.1k
1 vote

### Justification of discarding the backward wave in step potential scattering

The general solution to SchrÃ¶dinger's time-independent equation (for energy $E$) is \psi(x)=\begin{cases} A_1 e^{-i k_1 x} + B_1 e^{i k_1 x} & \text{for } x < 0 \\ A_2 e^{-i k_2 x} + B_2 e^{i ...
• 38.7k
1 vote

### Justification of discarding the backward wave in step potential scattering

Typically, we don't set $A_2=0$ - we set $B_2=0$. Our ability to do this is essentially a boundary condition. Because the Schrodinger equation is a 2nd order linear differential equation, there will ...
• 68.7k

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