The h Bar

12:50 AM

I like twitter more than Facebook. In twitter, when people follow me, I don't automatically follow them, and there is no friend request to be accepted.

user351417

2:30 AM

@EmilioPisanty Hm, I was thinking of writing a comment mentioning the word "troll", because that's what it sounded like at first, but for reasons I can't remember, I decided against it.

user351417

I didn't perceive anything particular about it, but I lost track of things somewhere in the middle because of the trollish impression. So I hadn't exactly read it fully.

user351417

I appear to have a declined rude/abusive flag on it.

David Z

2:55 AM

@Chair Probably a good idea; I think a comment calling out a post as a troll post is likely to cause more harm than good, mostly due to the significant probability of it not being accurate. Better to indicate that with a custom mod flag.

user351417

4:01 AM

@DavidZ Well, it could potentially help future users who may or may not choose to get out that rude/abusive flag to get the post deleted quickly in case no moderators are around.

David Z

I don't think it's worth it. If a post qualifies for a rude or abusive flag, in most cases it'll be obvious to pretty much anyone who sees it without the need for a comment explaining so; or if not, there are ways to comment that the post is rude/abusive without talking about trolling.

A comment that claims something is trolling is probably going to be eligible for flagging as rude/abusive itself.

user351417

@DavidZ Really? Wow, I didn't know that.

user351417

I guess I should have been more careful with this one... at some point I just started skimming because the bits I noticed were so... far-out-there, and I didn't notice any explicit mentions of mental conditions.

user351417

I guess that instantly deleting/not posting that comment was a bit of a close save for me :P

David Z

Yeah :P I mean, it's not the kind of thing you have a habit of posting, so if you had posted it and a mod was dealing with it, there's a good chance we'd just tell you not to do that rather than going for a formal warning or suspension. But it depends on which mod it is and whether they notice who posted the comment. Plus non-mods can cast rude/abusive flags and it is conceivable that a comment like that could accumulate six of them before a mod sees it.

Basically, calling someone a troll (even if they actually are) isn't compatible with the "be nice" principle, and it's something that we'd really like to discourage.

user351417

4:18 AM

Sure, I'll keep that in mind.

David Z

Cool, thanks.

I guess... for what it's worth, I personally think "unfriendly or unkind" (which is less severe) is probably a more appropriate response to a comment which calls somebody a troll, but I wouldn't really blame a person for casting a rude/abusive flag on it either.

Shing

5:01 AM

relativity still blows my mind. So I am sitting on my chair, perfectly "still". But I am not in an inertial frame (not in free fall). Do I misunderstand anything? It is kind of wired.

user8718165

5:30 AM

Hello sir @John Rennie

John Rennie

@user8718165 morning :-)

user8718165

Good morning sir

Sir I have some doubts regarding photoelectric effect

John Rennie

OK ... ?

user8718165

6:21 AM

@John Rennie,I was learning about this graph,
https://i.stack.imgur.com/PCUW1.png
I have interpreted the graph in the manner I have described below.
Please tell me whether my way of thinking is correct or not.
Let's suppose a beam of light emits 100 photons (which have higher energy than the work function of the metal used and have the same frequency) which strike the metal surface. Let's say out of these 100 photons only 70 are able to eject electrons and others are absorbed as heat and some other pass right through the metal surface without getting absorbed. Now I think that just after ea…

John Rennie

6:35 AM

@user8718165 I'm not sure what that diagram is showing. What is plotted on the x axis, and what are V1, V2 and V3?

user8718165

Sir, they are different frequencies...I want to know behavior at a particular frequency

and sir in the x axis the positive potential supplied by the battery is plotted.

John Rennie

6:49 AM

@user8718165 yes, that's correct.

Though the number of photoelectrons emitted per incident is actually very small.

About one electron is emitted for every hundred thousand to a million photons that hit the metal.

So it's more like 0.001% not 50%

user8718165

And sir, are all the remaining photons absorbed in some other manner?

Ok sir im sorry

John Rennie

The incident photon creates a photoelectron heading in the same direction as the photon i.e. down into the metal. That electron has to bounce off something to reverse its direction and head back towards the surface.

This is an unlikely process so most photoelectrons stay in the metal.

user8718165

And in the process many of them lose energy and some of them get trapped into the lattice back and the lucky ones with enough k.e reach the other plate. correct sir...?

John Rennie

Yes. I've answered questions on this on the main site ...

2

A: Kinetic energy of photoelectrons

Photoemission in the usual experiment is a two step process. First the incident photon creates a photoelectron in the bulk of the metal: The quantum efficiency for this is almost $100$% i.e. almost every photon that hits the metal creates a primary photoelectron. However this photoelectron is ...

user8718165

Sir thank you very much. I'm sorry I didn't find it. Yesterday I posted my question on the site and lost 2 rep.Then I deleted it.

2

also nobody answered my Q

Student404Mus

9:53 AM

@ACuriousMind They are written in the same format.

@ACuriousMind Hence, if you see them different it is okay to hear that difference

that's what I'm looking for

Anonymous

12:36 PM

@user8718165 Avoid deleting negatively voted questions; you'll hit the question ban soon that way.

Anonymous

You can undelete the question(s) from here‌.

user8718165

@Blue just did that because I thought My question was a nonsense. I got negative votes.

@Blue, I will surely try not to do that in the future

Anonymous

@user8718165 Yeah, that's what new users normally do. Try editing to improve the questions instead.

Anonymous

If you hit the question ban even moderators can't remove it.

user8718165

what will happen if I undelete it

John Rennie

12:42 PM

@user8718165 if you undelete it you get the -2 points again, but that's not the end of the world. Undelete it and post the link here and I'll have a look at the question.

user8718165

ok sir

0

Q: Doubt while simulating electric circuits

Today, I was simulating DC electric circuits just for knowledge and fun using PhET interactive simulations. But I'm having trouble understanding these circuits which I made. I think that both these circuits are the same(except for the ammeters used). Correct me if I'm wrong Now my question is ...

John Rennie

@user8718165 that doesn't have any downvotes ...

user8718165

Just deleted it... sorry for that

I just deleted that question because it had only one answer and I earlier said that it got negative votes because I just didn't remember. I deleted it without even properly seeing it. Won't do that ever again.

Good bye sir @John Rennie

John Rennie

@user8718165 bye

user8718165

1:21 PM

1

Q: Capacitors between two batteries

The positive terminals of both batteries are supposed to be on the right side Here I need to find the potential difference between the parts a and b. What I did was I assigned charge $q_1$ to the $2\mu F$ capacitor and $q_2$ to the $4\mu F$ capacitor. By Kirchoff voltage law I get $12- {{q_2}...

homework-and-exercises capacitance

aitfel

3

Q: Can path integral paths go backwards in time?

The paths can cross any coordinate at any time in the whole space (e.g. Universe space). Integration goes over all could-you-imagine paths. But time goes strictly forward. Can time variable resemble coordinate variable and path be able to expect backward turn? Upd 2014-01-04: yes, it's called sp...

quantum-field-theory path-integral antimatter

can anyone explain how does time goes backward in path integral?

user351417

2:50 PM

@EmilioPisanty (Perhaps @JohnRennie was talking about it that time too):

user351417

4

Q: Melting point of unsymmetrical dimethylhydrazine vs 1,2-dimethylhydrazine

Unsymmetrical dimethylhydrazine ($\ce{H2NN(CH3)2}$) has a melting point of $-57\,°\rm C$, but its isomer, 1,2-dimethylhydrazine ($\ce{(CH3NH)2}$) has a melting point of $-9\,°\rm C$. That looks to me like a significant difference, so there must be some mechanism which makes these two compounds ex...

organic-chemistry melting-point isomers

user351417

No answers after a couple of days... I'll give it a week before trying a bounty.

user351417

3:05 PM

Wait, I'm suddelny super confused. Can someone check out that discussion of hydrogen bonding and tell me if I messed stuff up?

user351417

Well, don't I feel stupid. I'm quite sure hydrogen bonding is a correct answer (though A.K's comment suggests otherwise)

user351417

My conclusion that 1,2-dimethyljydrazine should have a lower boiling point according to hydrogen bonding handwaving is completely incorrect.

user351417

With that steric hinderance reasoning, it should have a higher boiling point, as observed. Oops! I'll think it over and then write it out as an answer, and let the chem SE community see if it holds water :P

user351417

Perhaps I could use some information from the pubchem pages (1, 2) to support that reasoning nicely. The PSA statistics look like they could relate to the hydrogen bonding argument too, though I haven't checked if they make correct boiling point trend predictions.

Emilio Pisanty

3:21 PM

@Chair nicely asked.

user351417

Thanks =) A pity it's incorrect.

user351417

Also, I noticed that my writing kinda sounds like it's claiming that your speculation about symmetric packing was mine, but I included a link to the chat to make up for that

user351417

@EmilioPisanty I'm still wondering if it's worth tempting A.K. with a bounty... I'm not completely sure about the hydrogen bonding stuff, and s/he clearly has some other ideas. What do you think?

Anonymous

3:38 PM

@Chair There are several knowledgeable folks on Chemistry SE. If not A.K. someone else will probably answer. You'll be lucky if you can somehow rope in someone like Martin to write up one of their published-paper style answers. :)

Anonymous

3:55 PM

@Chair Placed a +100 bounty there.

Nanashi No Gombe

5:51 PM

Hi. Can someone answer this question please?

https://physics.stackexchange.com/q/461696/76347

Or, probably provide a reference here where I can learn about 't Hooft determinants? Thanks.

ACuriousMind

7:17 PM

@Student404Mus I'm not sure what you mean by the same format. In purification, we start with a mixed state $\rho$ as density matrix on a Hilbert space $H$ and turn it into a equivalent pure state $\lvert \psi\rangle$ on the space $H\otimes H$. In Schmidt decomposition, we start with a pure state $\lvert \psi\rangle$ in a tensor product of Hilbert spaces $H_1\otimes H_2$ and write it as $\lvert\psi\rangle = \sum_i c_i \lvert v_i\rangle \otimes \lvert w_i\rangle$. Where's the "same format"?

DanielSank

9:23 PM

Hi, everybody.

enumaris

9:38 PM

sup

ACuriousMind

inf

Scientist Smith YT

10:44 PM

@All How do we define the word “quantum” In quantum mechanics?

ACuriousMind

@ScientistSmithYT See physics.stackexchange.com/q/397694/50583

Scientist Smith YT

10:56 PM

@ACuriousMind I read the answer and question and I’m not sure I quite understand what the word “quantum” means in quantum mechanics? I’ve heard through some physicists that quantum just means a small effect.

ACuriousMind

@ScientistSmithYT The whole point of that question is that a proper definition of "quantum" is subtle and technical. The historical origin is that "a quantum" was supposed to be a discrete and small packet of energy (like the photons in the photoelectrical effect). But the usage of the word has far transcended its origins.

Scientist Smith YT

@ACuriousMind Oh. So it doesn’t mean what it used to mean back when the word was created?

ACuriousMind

For the exact development you'd have to ask a historian (e.g. at History of Science and Mathematics), but I believe that "quantum mechanics" rather quickly became a catch-all for everything related to the decidedly non-classical (i.e. not Newtonian/Hamitlonian/Lagrangian) mechanics Bohr, Einstein, Heisenberg, Schrödinger, etc. worked on

But in my view - which is not founded in any detailed study of history - "quantum" indeed originally referred to the "quanta of energy" in the photoelectric effect

Scientist Smith YT

Hmmm... that’s interesting

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