# Questions tagged [plane-wave]

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### Calculating in-duct sound intensities from sound pressure measurements with mean mass flow

In the time domain and in free field condition the sound intensity can be calculated as $\vec I(t)=p(t) \cdot \vec v(t)$ with $p(t)$ being the sound pressure and $\vec v(t)$ being the sound velocity. ...
47 views

### How to formulate the expression of this EM wave? [closed]

Consider a plane EM wave polarised parallel to the $(Oz)$ axis, this wave propagate in empty space with direction $\overrightarrow{OD}$ in the $(Oxy)$ plane with an angle $\theta$ from the $(Oz)$ ...
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### What is meant by "bases" not belonging to state space and how are they possible?

Section A3 of Chapter II on mathematical basis of QM in Cohen-Tannoudji’s "Quantum Mechanics" book has me a bit confused. The section is named ...
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### What is the graphical representation of a wave plane of the form $e^{i(\vec{k}.\vec{r}-\omega t)}$ or $e^{i(k.x-\omega t)}$?

Let's consider a plane wave of the form $e^{i(\vec{k}.\vec{r}-\omega t)}$ Is the graphical representation the following or the following ? I'm wondering what is now the graphical representation for ...
343 views

### How and why the state of free particle in quantum physics is represented by plane wave packet? [closed]

In Quantum Mechanics (Cohen Tannoudji) Topic: "Asymptotic Form Of Stationary Scattering States" It is written that for large negative values of $t$, the incident particle is free and it's ...
1 vote
835 views

### What is the propagation direction of plane wave?

As far I know, plane wave equation is given by: $$\vec{E}(\vec{r},t)=\vec{E_0} \cdot e^{i(\vec{k}\cdot \vec{r}-\omega t)} \hspace{2cm} \tag{1}$$ In some textbook propagation direction of $(1)$ is ...
238 views

### Finding helicity eigenstates

Question: Give the mode expansion of the $A_i$ in terms of plane wave \begin{equation} \epsilon^{\pm}_i(p)e^{-ip \cdot x} \ \ \ \ \ \text{ and } \ \ \ \ \ \epsilon^{*\pm}_i(p)e^{-ip \cdot x} \...
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### What Plane Waves Make a Gaussian Beam?

When I think of a light beam, what first comes to mind is this: Black lines are axes (both spatial axes, at a snapshot in time), and blue lines represent the surfaces of constant phase of a plane ...
374 views

### Determining plane wave polarization given the magnetic-field vector phasor

Given the following magnetic-field vector phasor: $$\vec H(\vec r)=\left[\hat x - j\hat y\right]H_o e^{jkz}$$ I need to find the associated E-field vector phasor so that I can determine the ...
1 vote
293 views

### Few doubts in the solutions of step potential in Quantum mechanics [closed]

Assume we have a step potential $$V(x)=\left\{\begin{array}{ll} 0, & x<0 \\ V_{0}, & x \geq 0 \end{array}\right.$$ and we fire particles from a distance $s$ towards the barrier from the ...
318 views

### Why is the plane wave ansatz appropriate for scattering cross sections of a localized particle beam?

This question is a spin-off from this related question: Why does the Born approximation for the scattering amplitude depend on the potential $V$ everywhere in space, unlike classical scattering? This ...
I've recently come about the free plane wave solutions to the Dirac equation, and i'm having a hard time proving that the normalization factor $n$ is $$n=\frac{1}{\sqrt{2m(m+\omega)}}$$ Where $\omega$ ...