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ZeroTheHero

2:19 AM

@Slereah if you’re into this you’re gonna love languagelog.ldc.upenn.edu/myl/Stuperspace.pdf

1 hour later…

Hrishabh Nayal

3:45 AM

Hey guys! A quick question : Is the color of light it's wavelength or it's frequency? Like if light goes from air to say glass it's frequency does not change but wavelength changes. So if somehow I could be inside the glass and see the light inside it, would it's color change?

I feel like this should already be on Physics.SE but I can't find it

BioPhysicist

@ACuriousMind Looks like it was closed again for the same reason :(

@Slereah The red box lowers the quality a little bit

skullpatrol

4:12 AM

I think, Slereah put the red box in for illustrative purposes

but yeah, I question its quality for other reasons

Superfast Jellyfish

@skullpatrol some pdf readers automatically put a box around links

skullpatrol

@SuperfastJellyfish that must make them a pain to use with exponents and links?

1 hour later…

John Rennie

5:19 AM

@HrishabhNayal the colour is determined by the energy per photon because that is what determines how it interacts with our eyes.

And the energy per photon is hf, so it's the frequency that matters.

skullpatrol

frequency matters a lot in life also

ie the things you frequently do

Yashas

6:23 AM

Q: When solving Schrödinger's equation by separation of variables, why is the separation constant taken as the energy?

For simplicity, let's take the 1D Schrödinger's equation for a single non-relativistic particle: $$-\frac{\hbar^2}{2m} \frac{\partial^2 \Psi(x,t)}{\partial x^2} + V(x) \Psi(x,t) = i\hbar \frac{\partial\Psi(x,t)}{\partial t}$$ Applying separation of variables, $\Psi(x,t)=\psi (x)\phi (t)$, we get...

> the definition of energy in quantum mechanics -- it is $\hbar$ times the rate of change of phase

The phase part of the wavefunction doesn't matter a lot if you are in an eigenstate. I can get energy E after evaluating the expected value of energy of a time independent solution. So energy can be found in places where the phase has no role to play?

Hrishabh Nayal

@JohnRennie ok. Thanks!

Yashas

Oh, I think there is circular logic. The E comes out of the $\langleE\rangle$ of the TISE solution because E the separation constant was assumed to be E. So E was defined when the wavefunction was split into the position part and time part. That's how it ends up in the TISE solutions I guess.

I am disappointed that two textbooks I am using did not give this definition; they just said assume the separation constant is E without giving any motivation (except that it meets the dimension requirements). Or I have been a bit too dumb to realize this without help.

3 hours later…

Mad Spaces

9:27 AM

Good day.
Is the ideal gas equation only valid for gases which is made up of one atoms?

since in the derivation which sets for the degrees of Freedom f= 3 (trans degrees) and odes not consider rotation or Oscillation

Slereah

Ideal gas is always an approximation, and it can also be approximating non-monoatomic gases

although of course, the thermal capacity will differ from monoatomic gases

also at low enough temperatures, even a non-monoatomic gas is unlikely to activate its non-translational dof

Mad Spaces

Oh okay so i am right.

Well thank you for the answer. Can i still use in the a university level courses?

Aka.. consider gases like O2 or N2 to be ideal and use Pv=nRT?

Slereah

should be fine, as long as you're not considering them in particularly extreme conditions

Mad Spaces

Thank you

Aman Singh

9:43 AM

skullpatrol

10:21 AM

3 hours later…

Roberto Valente

1:18 PM

Hello guys, can anyone confirm if this statement is accurate? It’s information present on this site and I can’t find much corroboration anywhere else.

“The wave equation may allow any shape wave front, but Huygens principle does not hold for any shape wave front. For example cylindrical waves do not propagate 'cleanly' without a wake whereas spherical waves and plane waves do”

A simple answer would suffice. It’s giving me a headache.

Mohamed Obeidallah

1:43 PM

Is there anyone here who are familiar with particle physics or accelerator physics especially in generating gamma rays?

ACuriousMind

@MohamedObeidallah just ask your question, if someone knows the answer and wants to answer it, they will

Mohamed Obeidallah

According to this link https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf, HERMES III at Sandia National Labs can generate very large area gamma rays by converting the electron beam into bremsstrahlung radiations after hitting the tantalum target. As we can see in the isodose contours in the linked article especially at page 40, the gamma ray field is indeed huge. It makes sense since the target size ranges from the size of transistors to the size of military tanks.

Here, in this link https://spie.org/news/3737-gamma-ray-generation-using-a-laser-accelerated-electron-beam?SSO=1 it was sa…

ACuriousMind

@RobertoValente why would the principle depend on the shape of the wavefront?

Roberto Valente

2:07 PM

I thought it was odd, too.

I believe the user was implying that cylindrical waves, *for some geometric reason*, did not propagate “sharply”, because Huygens wavelets - outside of the new wavefront - wouldn’t completely cancel each other, leaving a “wake” behind the wavefront.

I always assume to know less around here, and the information was from a rather prominent user, so that’s why I questioned. Thank you for the attention, though, very glad for the feedback!

skullpatrol

2:30 PM

Thanks for asking! Feedback is one of the reasons chatrooms exist :-)

3 hours later…

Charlie

5:21 PM

What do we mean by a field "coupled to a source"? Is the implication that the field is being excited at a/some point(s)? A bit like taking a net and shaking it up and down at a point?

(the net analogy may or may not be taken seriously)

Slereah

there is an interaction term with the field, but that term isn't another field

it's an arbitrary source, that is either a mathematican nicety, or an actual apparatus generating the field

similar to how in thermodynamics, we allow for terms in the equations that are sources and sinks of heat

2 hours later…

Charlie

7:01 PM

@Slereah Sorry I had to immediately leave after asking this. So the "source" is just a self interaction in the field?