Phase Velocity Puns

So I just read that it's possible that the group velocity can be greater than the phase velocity. But I didn't find any specific examples. Can somebody mention some possible ways for this to happen?

The velocity of waves through the medium of refractive index $\mathrm{n}$ is $\sqrt{n / k}$. The group velocity in the medium is

(a) $\frac{1}{3} V_{p}$

(b) $\frac{4}{3} V_{p}$

(c) $\frac{1}{2} V_{p}$

(d) $\frac{2}{3} V_{p}$

That is the question. I tried solving it in two ways and I am getting different answers.

My solution: https://i.imgur.com/KCy6goD.png

(I am unable to attach my solution here) So sending the link.

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I have a process which outputs a signal that could be modeled as 1+cos(w(t)+v*t) where w(t) is a wiener type process and v is the phase velocity. Using Fourier analysis it's pretty easy to measure the phase using a phase unwrap algorithm, but the one thing it doesnt seem to measure is the sign of v. I'm my specific case, the sign of v has physical meaning and I would like to extract it from the data that I measure. Perhaps by looking at some other component or doing a different analysis on the data. Any suggestions or questions are most welcome!

Edit: Just to be clear, even if the method would require new modulations or data to be taken in a different way, that's all fine. I'm just curious about methods to figure it out. At least having a wide range of ways to find it would help push me to some final method of figuring it out.

When should one introduce critical velocity workouts? Is it good to include fartleks at CV even during the base phase?

>Nimbus Cloak (S2)
Changed from [shortly after casting your Ultimate] to [Shortly after casting a Summoner Spell]
>
>Movement speed increased from 100 to 150

This setup seems sticky as fuck... Why is it not a thing? Edit: and nimbus cloak!

Currently taking a class called waves and oscillations. This was asked in an assignment. I'm to draw a plot of a bouncing ball in the phase space (space of momentum and position). I already know its velocity (v(t) = -gt +v0) and position (x(t) = -0.5gt^2 +v0t + x0). How do I go from here to mv(x)?

I tried plotting it as a parameterized curve where y = m(-gt +v0) and x = -0.5gt^2 +v0t + x0, and I do get something sensible (a parabola that's rotated 90 degrees). Is that all there is to it? This was not covered in the lectures, and the book we use barely mentions the phase space. Google is not very helpful as well, gives me a lot of quantum physics when I try to search.

I've been looking around the internet and can't find a satisfactory answer. I was thinking about how dielectrics slow down the group velocity of light, but not the phase velocity, and then wondering if that would violate causality in some way. Apparently, the reason why it doesn't violate causality is because a pure sine wave doesn't carry any useful information because all it gives is a frequency. In the context of practical uses, it may not be very useful since there's no information about phase or amplitude, but in the context of photons however, it seems like there's enough information to know a lot. You know the energy using Planck's relationship E=hf, and you know the wavelength by the relationship c=lambdaf. What's missing?

Hi everyone, I'm an undergraduate student currently taking a waves course and stumbled upon some conflicting things I was taught.

When I was introduced to the refractive index the argument was made that it must be >=1. The reasoning given was that nothing could travel faster than light which was acceptable. Then while taking this course I was told that phase velocity can exceed the speed of light as it carries no information and given n=c/v(p), one could rightly assume that n could very well be less than 1.

Where is the flaw in my line of thought? Am I missing something?

Sorry for my bad formatting, I'm not familiar with LaTeX on Reddit.

Hi all

I am trying to determine the position and velocity of a target moving along a 1D axis using noisy measurements, my position estimation is fairly accurate however for some reason my velocity estimate is slightly out of phase with the actual velocity and I cant figure out why, does anyone have a suggestion?

thanks

https://preview.redd.it/iz4nka174a921.png?width=1019&format=png&auto=webp&s=9b475f98454baabd34df816bea76027cabd4934a

A recently submission to /r/science: http://www.reddit.com/r/science/comments/1oewpk/new_material_gives_visible_light_an_infinite/

From here: http://phys.org/news/2013-10-material-visible-infinite-wavelength.html

Talking about this paper:http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2013.256.html

Permittivity of light in materials is a strange concept that I don't feel like I have a strong grasp of. Why does silver have a negative permittivity and silicon nitride positive? Is this related to the optical rotation of light? How are the photons interacting with the material's electrons?

Can a sound wave have different group and phase velocities? If so, how can I make one (using multiple sine wave generators)?

It's fun, try it.

That's all.

So I was looking at the rule for VT’s, and it says “add 1 to hit rolls when the model shoots at a unit that can FLY.” Because there is no phase indicated, does that mean you can add 1 while firing Overwatch against models that can fly?

I can't get my head around this.