The h Bar

12:58 AM

Hi there, This has maybe been asked before (and links to questions and answers on the site are welcome), but how come an electric field of the type $C\frac{\boldsymbol{\hat{r}}}{r^2}$ (where $C$ is some constant) has a divergence of $0$ everywhere except at the origin? If one sketches the field, it seems like there is a positive divergence beyond the origin as well.

schn

1:21 AM

In Introduction by Electrodynamics by Griffiths, the divergence of the $1/r^2$ field (for $C=1$) is defined as $4\pi\delta^3(\mathbf{r})$. This definition solves the paradox with the divergence theorem, but is it also consistent with the divergence of the field? Is the field really 0 everywhere except the origin?

ZeroTheHero

3:15 AM

@Student404Mus preprints on ArXiv are not strictly peer-reviewed but the submissions “are subject to a moderation process that classifies material as topical to the subject area and has scholarly value”. vixra removes the “scholarly value” barrier, which is a statement about the quality of work you find there.

Answer Seeking Penguin

4:26 AM

can I send my reddit profile here I have posted four OG memes there

https://www.reddit.com/user/rookiephysicist/posts/
here it is anyway

based on physics of course

Answer Seeking Penguin

4:45 AM

and please can someone answer this question of mine on physics SE :-(
https://physics.stackexchange.com/questions/541825/why-does-hamiltonian-no-longer-commutes-with-mathbf-l-and-mathbf-s-in-pres

ZeroTheHero

4:57 AM

@AnswerSeekingPenguin why do you show up as “dumb as a rock” on the question? are you using 2 accounts to post on PSE?

Answer Seeking Penguin

@ZeroTheHero I don't know I tried changing that affect didn't took place

ZeroTheHero

so you are using two accounts on PSE. Did you upvote you own question?

exp ikx

Hey, does anyone here have a good introduction material on quantum switch (quantum information topic)?

Answer Seeking Penguin

@ZeroTheHero no man this account and dumb as rock are same you can try going yourself

Yuvraj Singh...

Morning.

Answer Seeking Penguin

5:09 AM

@expikx want to go rough ? DJ Griffiths Introduction To QM wanna go smooth ? Nouredine Zettili

@YuvrajSingh... suprabhat

exp ikx

@AnswerSeekingPenguin Introduction to QM has quantum switch?!?!

Answer Seeking Penguin

@expikx I meant to say there are two diff books if you seek adventure go with DJ Griffiths otherwise use Zettillliii

exp ikx

@AnswerSeekingPenguin I don't think you are referring to the same concept. Quantum SWITCH is recently introduced (in 2013 IIRC).

Answer Seeking Penguin

@expikx then I don't know sorry

user434058

6:18 AM

@AaronStevens Nice!

Yuvraj Singh...

@AaronStevens hi.

@JohnRennie hi.

John Rennie

@YuvrajSingh... hi :-)

I'm going to be busy for a while I'm afraid. Monday morning :-(

Yuvraj Singh...

@JohnRennie ah! No issue sir :-)

Actually I was reading about sound waves. From my physics magazine.

And I have a question why we consider the sound as an adiabatic process?

John Rennie

6:40 AM

@YuvrajSingh... The compression and expansion happen fast in sound waves. The frequencies of sound waves are typically in the range 100Hz to 10kHz so the periods are from 10ms to 0.1ms. These times are so short that heat conduction through the air is small.

Though in fact the errors in the adiabatic approximation are not completely negligible.

Yuvraj Singh...

7:08 AM

@JohnRennie it is just an guess only?

@PM2Ring hi, sir.

John Rennie

@YuvrajSingh... ah, there's already a question about this ...

10

Q: Why are sound waves adiabatic?

I want to know why we can treat sound waves as an adiabatic process. Precisely, I know that pressure and density vibrations occur so fast that molecules have no time to exchange energy (I might be wrong). But I would like a deeper explanation, not using a mathematical argument, but maybe a physic...

Yuvraj Singh...

7:25 AM

Oh

PM 2Ring

7:56 AM

@YuvrajSingh... Hi. Here's another blues song for you, Stray Cat Blues, written by The Rolling Stones, but I think this version by albino Texan Johnny Winters is the best version. I suppose I should mention that the lyrics are not politically correct...

Johnny Winter - Stray Cat Blues

►

ACuriousMind

8:39 AM

I've used our coffee machine more in these last few weeks than in the years before that and I'm starting to think it just makes terrible coffee :P

Yuvraj Singh...

I too use electric kettle to boil water for coffee.

And it taste better than a taste coffee made by a machine!

John Rennie

Over the years I gradually realised that coffee is just a lubricant for working, and if I'm concentrating hard I don't even realise I'm drinking it until suddenly the mug is empty. So these days I buy instant coffee, and it seems to work :-)

Yuvraj Singh...

Same here :-P

I usually have two to three cup's of a coffee a day!

PM 2Ring

I like my coffee fairly strong, and I don't enjoy the flavour of most instant coffee, but I'll drink it if there's no real coffee available. Moccona is ok, I suppose. Also, I find that instant coffee has a stronger diuretic effect than real coffee.

Yuvraj Singh...

@PM2Ring do you have songs like you had posted yesterday?

John Rennie

8:49 AM

@PM2Ring that's an essential role. It forces me away from the desk every hour or so, plus I get exercise running up and down the stairs :-)

PM 2Ring

:D

user2723984

Hi everyone, I have a quick question, does anybody know whether there a simple formula for the number of nearest neighbors of a point in a D-dimensional square lattice, N? For example, in 1D, N=2, in 2D, N=4, in 3D, N=6, so it seems that N=2D, do you know if this is true?

ACuriousMind

@JohnRennie I agree with the first part, but I do notice what I'm drinking, unfortunately ;)

If I ~~liked~~ could stomach energy drinks I'd probably not bother with coffee...

PM 2Ring

@YuvrajSingh... I've been trying to think of songs that you'll like. But musical taste is a subjective thing, and it's affected by all the other music you've ever heard. So it's difficult for me to know what will appeal to you. Especially since you haven't given me very much feedback about the songs I've posted.

@user2723984 Yes, that's true. 2 points for each dimension, 1 on either side of the original point.

ACuriousMind

@user2723984 Yes, that's true - you should be able to convince yourself that each dimension just adds two nearest neighbours along the axis in that dimension.

user2723984

8:57 AM

@PM2Ring makes sense! Thank you both

it's easy to picture until 3 dimensions, my brain has a bit of trouble extrapolating after that

PM 2Ring

And if you want to include diagonal neighbours, then it's 3^D - 1. But of course the distance to the diagonal neighbours gets rather large for large D. Eg, if D=100, the neighbours on the long diagonal are sqrt(D)=10 units away.

@YuvrajSingh... Here's a sweet love song, with some lovely slide guitar playing. Let me know what you think of it.

Duane Allman with Cowboy- "Please Be With Me" (1971)

►

PM 2Ring

9:19 AM

A bluesy number from Chantel, which was written by Bob Ezrin and Michael Kamen and was first released by Tim Curry.

Sloe Gin performed by Chantel McGregor

►

John Rennie

I heard this on the radio (Planet Rock) this morning and it's the first time I've heard it for ages. I'd forgotten how much I liked it.

Canned Heat - On The Road Again [HQ]

►

Although I'm not especially keen on Canned Heat's albums.

Yuvraj Singh...

@PM2Ring amazing!

I heard it twice.

I agree with you, I love rock songs, and I have quite good amount of albums in my PC

PM 2Ring

@YuvrajSingh... Oh good. I used to play that song on guitar, but I'm not as good as those guys. :)

Here's a link to all the YouTube songs I've posted in this chat, in case you missed some of them.

Here's a classic example of Southern Rock, with incredible dual guitar playing by Duane Allman & Dicky Betts.

The Allman Brothers Band - In Memory of Elizabeth Reed ( At Fillmore East, 1971 )

►

@JohnRennie Canned Heat were (are) a great jam band, but the quality of their stuff is rather variable IMHO.

I was at an "open mic" day a couple of years ago when some friends asked me to sit in with them to play some blues harp on On The Road Again. I was a bit hesitant because I'd never tried playing it before, and it's not a straightforward 12 bar blues. So I went away & spent a few minutes trying a few things out. Anyway, I agreed to accompany them. I wasn't totally happy with what I did, but the band & the audience seemed to think it was ok. :)

Oops! I forgot to post that link. chat.stackexchange.com/…

ACuriousMind

9:46 AM

Since apparently we're posting music now - have some prog metal:

Mastodon - The Czar [Official Visualizer]

►

Yuvraj Singh...

Lol

And lol

Look like a dumb face lol

ACuriousMind

10:03 AM

?

Yuvraj Singh...

Sorry sir by mistake!

PM 2Ring

@ACuriousMind I don't mind that. At the start, the scale they use reminded me a little of Led Zep's No Quarter. I generally like the guitar work in metal, but I don't like the excessive use of dark themes in the lyrics. And I hate "growl" vocals. I suppose I can blame Pink Floyd for growl - the earliest example I can think of is in One Of These Days, the 1st track on Meddle. But at least that's only got 1 line of vocals. :)

ACuriousMind

I expected something like that and chose something on the non-growly end of the spectrum ;)

Though one of my favourite songs contrasting both growls and clear vocals is youtube.com/watch?v=SQNtGoM3FVU

PM 2Ring

Chantel likes a bit of metal. A lot of her originals have a strong metal influence, although recently she's been getting rather avant garde. But here's her cover of a Steve Vai piece:

Chantel McGregor Band - For the love of God - The Brook Southampton, England on 26.04.10.

►

@ACuriousMind It's brilliant, and I see how the growl works in it, but it's just too much for me. And way too dark.

@ACuriousMind The singer on that track reminded me of a slightly scary Finnish blues singer:

What Have I Done Ina Forsman with Helge Tallqvist Band

►

ACuriousMind

10:28 AM

@PM2Ring Sorry, I think this is already the least dark I can do ;P

PM 2Ring

@ACuriousMind That's ok. :) More Ina, doing a Nina Simone number:

Ina Forsman - I Want a Little Sugar in My Bowl

►

ACuriousMind

@PM2Ring Well, I'd bet she could do a mean growl, too ;)

PM 2Ring

I'm sure she could. :)

Here's one of Chantel's metal-ish songs. There are numerous live clips of this, but the audio quality isn't great. For some reason, in many of her live clips the drums are too dominant, IMHO.

Chantel McGregor - Walk On Land (Audio)

►

Sir Cumference

10:45 AM

sigh realized this makes no sense

PM 2Ring

Another original, with a prog / metal feel. It takes a while to get going...

Chantel McGregor, April,100 Club,London,2 2 2018

►

Justin

11:11 AM

what's the uncertainty of an ohmmeter?

is it +- 0.1 ohms?

Sir Cumference

depends on the ohmmeter

Justin

generally is it 0.1 ohms?

Slereah

Morning

PM 2Ring

@Justin It depends on the meter, and on the resistence range you have it set at. Remember, an ohmmeter is really an ammeter, measuring the current through a standard resistor.

Justin

Ok... thank you!

ACuriousMind

11:15 AM

@Slereah good afternoon :P

Sir Cumference

happy 7am

Slereah

@ACuriousMind The laws of time have stopped ever since the pandemic

ACuriousMind

Unfortunately, my daily meeting schedule disagrees :P

PM 2Ring

After all that dark stuff, here's something lighter, with a great "guitar battle" between Derek & Susan at the end. Unfortunately, the camera work mostly focuses on Derek, so we don't get to see much of Susan's great lead playing.

Tedeschi Trucks Band ..Learn how to Love (Live)

►

ACuriousMind

@SirCumference I've never found anything 'happy' about being awake at 7am...

2

PM 2Ring

11:26 AM

Here's a Ray Charles cover, with Susan singing & playing her little heart out:

That Did It Tedeschi Trucks Live Fillmore

►

I think that's probably enough music from me for today. :)

Emilio Pisanty

12:05 PM

@ACuriousMind It's the Director of Public Q&A getting told off by a ~~fired~~ former report that she doesn't know hot to apologize, and then pretty explicitly validating that criticism in public

that's pretty exceptional on my books

but why the hell did they have to wait until this was an extramural conversation to have it?

why on Earth didn't that conversation happen intramurally and before they made such catastrophic choices?

Loong

@EmilioPisanty jlericson.com/2020/04/03/pronoun_retro.html

Slereah

1:07 PM

amazon.fr/Global-Theory-Connections-Holonomy-Groups/dp/…

Why is it so expensive

Novalium Company

@Slereah Because the person has set that price on the website

Slereah

Probably not

High prices on amazon usually means automatic pricing software

Novalium Company

I think the real question is how was this painting sold for 46 mil

i'm becoming a painter now

Slereah

That painting's upside down

Amateurs

Novalium Company

I'll just buy a blank canvas and sell it for 10 mil

ACuriousMind

1:18 PM

truly beautiful how the market regulates itself

Novalium Company

"European air particles have touched it"

let me open paint one sec

ACuriousMind

@Slereah it must be a conspiracy preventing you from unlocking the secrets of holonomy

Slereah

@ACuriousMind I already uncovered the secret of holonomy

Connection goes round

ACuriousMind

reminds me that the origins of that name are a bit mysterious - it means something like "all-encompassing law" but no one is quite certain why it was chosen

Novalium Company

done selling for 20 min

if you want the text removed, you'd need the premium license for 30 mil

Slereah

1:22 PM

Apparently introduced by Mr. Cartan

Oh wait, that was for manifolds

who introduced holonomy

Novalium Company

anyone wanna buy my painting? i really need funds for my product

Loong

@NovaliumCompany You would need to die first.

Slereah

Cartan just says "holonomy" without introducing it

So I assume it is older

Novalium Company

@Loong yeh and then price increases each year

the sad thing is that no one recognizes me as an artist now :(

I guess I'd really have to wait 500 years for my masterpieces to be appriciated

Okay, I'm selling it for 10$

(doesn't seem that expensive now huh, the power of psychology)

anyone pliz

i accept peipau

I'm in the middle of my chemistry online class don't blame me

the teacher's gibberish is a really soothing background music

Slereah

I think I can probably define the holonomy of a GR measurement if 1) the observer is geodesic 2) it has a Fermi basis

That way all the vector transport can probably be eventually related to a single parallel transport

Novalium Company

1:26 PM

By the way, I'mma be making a plaster mold from a baked polymer clay, hope it works

wish me luck #blessed #products #instagram

Slereah

oh and perfectly orthogonal reflection, I suppose

Novalium Company

can we please talk about my painting Slereah

it's important.

ok enough joking gotta go

ACuriousMind

there's nothing wrong with making a joke that's been done before a hundred times but insisting people react to it is a bit much :P

@Slereah I thought Fermi coordinates always existed, can they fail to?

Emilio Pisanty

1:44 PM

@Slereah I feel zero sorry for you, mate

and that's just volume I of five

Slereah

@ACuriousMind The issue is more that a real device may not define a Fermi frame

ie a real observer can have its axis rotating

ACuriousMind

just tell them to hold still

Slereah

I mean it would be nice, but then I could also ask for every object to be spherical, too

user434058

You guys use amazon.fr?

Slereah

yes, that is a common thing among french people

user434058

1:47 PM

@Slereah Are you French?

user434058

Also, Emilio is from Spain still.....

user434058

@Slereah BTW did you receive any message from a smart robot?

Slereah

No.

user434058

@Slereah Where do the messages written in the Contact section of your website go?

user434058

I mean this page.....

ACuriousMind

1:54 PM

Why the five periods?

A standard ellipsis is three periods.

user434058

I'll use $\dots$ from now on $\dots$

ACuriousMind

That doesn't really answer my question (I've really always wondered about these - to me completely baffling - typographic choices people make) but I'll take it :P

JMac

@FakeMod That seems like a step in a weird direction... Now people without chatjax will have a hard time seeing what you are trying to show.

user434058

@ACuriousMind Yeah exactly. What's the point of using only 3 dots, why can't wemuse 4 or 5 dots....

user434058

@JMac I was jk

user434058

1:59 PM

Apr 3 '17 at 19:52, by AccidentalFourierTransform

can we fire ACM?

user434058

Seems like being uncomfortable with ACM has been a tradition? :P

ACuriousMind

@FakeMod Standardized punctuation makes reading messages easier - questions end with '?', exclamations with '!', and sentences that are trailing off with '...'. Everytime I see unconventional punctuation I have to think about whether the author meant anything by it or whether it's just disregard for clear communication.

user434058

@ACuriousMind That seems a good reason and thus I am convinced. Thank you!

user434058

Sep 27 '16 at 13:12, by Danu

We all want the enormous ego of the pompous ACM PUNCTURED :P

user434058

Another example...

user434058

2:04 PM

@ACuriousMind I hope you're fine with me posting that, I just intend them to be a joke, no real hate or something like that :)

ACuriousMind

Another reason is to be able to use deviations from standard punctuation as a means of expression. For instance, I can express extreme bewilderment by using multiple question marks - '???' - but only if I otherwise consistently use only one. If I always use a random amount of punctuation, I lose that dimension of expressiveness.

@FakeMod Where's the joke? You're just citing messages out of context that were clearly meant ironically in context.

Slereah

The messages go to a database

That I check every few months

I mostly get spammers and John Duffield

3

user434058

@Slereah Oh! So do you ever see them?

ACuriousMind

@Slereah Ah, dev/almostnull/

Slereah

I do

user434058

2:05 PM

@Slereah expected!

Slereah

A lot of robots see my site and think "This site needs some marketing!"

user434058

22 hours ago, by FakeMod

@ACuriousMind No problem! None of my statements are expected to be funny for anyone except me.

JMac

@Slereah "This site is severely lacking in information about male enhancement pills. It is my duty as a bot to remedy this."

2

Slereah

Nah, not so much

Most of them are more along the line of SEO services

user434058

@ACuriousMind But what if one is always at the extremes? Don't answer that...

JMac

2:10 PM

@Slereah Probably more practical spam nowadays, but my first thought for spam is always male enhancement.

It's a classic.

user434058

@Slereah Has anyone ever hacked (or tried to hack) your website?

Slereah

Male enhancement spams are more for individuals

not websites

@FakeMod probably?

ACuriousMind

@FakeMod 'It's not meant to be funny to you' is the worst answer to 'Where's the joke?', especially when your messages could be (mis?)understood to be confrontational in nature.

Slereah

My site isn't super well protected, but I took the basic precautions

And so far nothing bad happened

user434058

@Slereah good!

ACuriousMind

2:12 PM

Sure, jokes can misfire sometimes, but if you find yourself consistently failing to be funny to anyone but yourself, you might want to revisit your notion of 'joke'.

Slereah

Also I don't think anyone would really care to pirate my site

So if any attack happens, it will be from a bot

and bots can usually just exploit very obvious defects

But y'know, I took the basic precaution

No SQL injection on my site

user434058

@ACuriousMind Alright!

user434058

@Slereah I was thinking exactly about that :)

user434058

@ACuriousMind I find it hard to be funny when I am chatting with someone who can neither hear me or see me, so I tried to use other people's jokes to sound funny.

user434058

But yeah, I don't need to be funny.

user434058

2:24 PM

@ACuriousMind Also, why are you so solemn all the time? I mean I don't take everything literally and at it's face value and let some things be as they are. I am not at all criticizing you, in fact I shoul be (and thus I am) thanking you for teaching me and pointing out the stuff which I was doing wrong. But at the same time, I find your perfection and meticulousness to be a bit too much and that probably might be because I haven't met people like you before, who are this much careful about...

user434058

... everything and critically analyse every move they make.

user434058

Or the moves that other people interacting with them make.

ACuriousMind

@FakeMod I wouldn't characterize myself as 'solemn all the time' - I make plenty of jokes and tongue-in-cheek comments in here and elsewhere. What's true is that I care about communication and I want others to do so, too. Words matter, and when you say something that I disagree with - or that I think could be construed as inappropriate - I think it better to let you know than to let it slide until it becomes a larger prblem.

It's not about taking things literally - but when you say stuff (yes, even when you're "just joking", since jokes in bad taste can be harmful, too), I think you should expect others to hold you accountable for it.

This is a public chat, and its transcript is permanent. it's not a fleeting private text message, and things said here won't disappear.

user434058

@ACuriousMind I completely agree. I think you're just too German for me :P

user434058

I am sorry if that joke didn't make any sense.

ACuriousMind

2:44 PM

You're not the first one to tell me that, but I'll maintain I'm exactly the right amount of German until I get an actual argument against it...

Slereah

@ACuriousMind what do you eat for breakfast

ACuriousMind

usually a Brötchen with salami and cheese

Slereah

I have finished watching Tiger King

Apparently everyone involved in private tiger ownership is involved in some manner of polygamist sex cult

JMac

@Slereah Well considering that private tiger ownership and polygamist sex cults are practically the same thing, that makes total sense.

ACuriousMind

I'm confused...how does the tiger sex cult relate to my breakfast? Inquiring minds want to know.

Slereah

2:54 PM

Unrelated

ACuriousMind

not sure whether I'm relieved or sad about that

Slereah

At least I hope so

The breakfast was just to ascertain your germanness

user434058

@ACuriousMind Anyways, Danke Schön (didn't use any translation service) for correcting me when I was wrong. :)

PM 2Ring

Guy 1: "Did you know that during the mating season, lions have sex several times a day?"
Guy 2: "Damn. I just joined Rotary."

For those that don't get the joke: en.wikipedia.org/wiki/Lions_Clubs_International & en.wikipedia.org/wiki/Rotary_International

John Rennie

I'm sure the British Lions wouldn't do that.

Yuvraj Singh...

3:31 PM

@JohnRennie hi, what for today?

John Rennie

@YuvrajSingh... I fast on Mondays

That isn't so hard to do since my Sunday meal is usually so large it takes me two days to digest it :-)

Yuvraj Singh...

OK. Large meal?

John Rennie

I think I posted a picture of the Sunday lunch yesterday. Let me have a quick search ...

Here

Yuvraj Singh...

Just an pasta!

kauray

hi, i was watching leonard susskind's lectures, in the second lecture he explains Newton's Law F=ma, and says that we need the velocity information in this scenario, my question is if we know the position of the particles is that not enough to use Newton's Law?

John Rennie

3:35 PM

@YuvrajSingh... Chicken with and chillis and capsicum in a cream sauce with pasta

@kauray I haven't seen the lecture, but I suspect he means that to predict how the object moves you need to know both the position and the velocity at time zero.

@kauray for example suppose you have two cars at the same position at time zero, but one is stationary while the other is moving at 100 mph. Their positions are going to be different at later times.

So just knowing the car position isn't enough.

kauray

@JohnRennie oh okay thanks!

John Rennie

This is sheer genius and an eloquent testimony to the ingenuity of human beings when it comes to keeping themselves entertained during the CV lockdown. I am not worthy.

kauray

@JohnRennie if we knew the velocity, then would Newont's equation F=ma predict how the vehicle moves? Wouldnt it just give the force acting on the body?

John Rennie

@kauray typically what we do is rewrite the equation as a = F/m. The reason for doing this is that it gives us the differential equation:

$$ \frac{d^2x}{dt^2} = \frac{F}{m} $$

where $F$ may be a constant or may be a function of time.

Then we can integrate the equation to get the velocity:

$$ v = \frac{dx}{dt} = \int \frac{F}{m} dt $$

But when we integrate we get a constant of integration, and we need an initial condition to determine the value of this constant. A typical initial condition might be to set the value of the velocity $v$ at time $t = 0$.

@kauray OK so far?

kauray

yup okay

John Rennie

3:49 PM

And then to get the position as a function of time we integrate again:

$$ x = \int v(t) dt $$

and again there is a constant of integration that we need a second initial condition to determine. Typically this would be the position, i.e. value of $x$, at time zero.

kauray

So the velocity basically serves as the initial condition of the differential equation right?

John Rennie

Correct.

We need two initial conditions because to get to the position from the acceleration we need to do two integrations.

kauray

I didnt get :
And then to get the position as a function of time we integrate again:
$$ x = \int v(t) dt $$

John Rennie

We start with the acceleration, and when we integrate the first time we get the velocity because $v(t) = \int a(t) dt$. Yes?

kauray

Yup

Then another integration to get the position?

John Rennie

3:53 PM

Correct! :-)

kauray

okay thanks, maybe i should have asked this in a separate chat room, it got cluttered in here

John Rennie

@kauray we do have a room specifically for questions like this link here but you are welcome to ask here as well. It's quiet anyway so no-one is going to mind :-)

kauray

Ah this was more so a concept question rather than any problem oriented question I thought

John Rennie

Yes, and it's fine to ask here.

If a conversation looks like it's getting long and involved sometimes we encourage people to take it to another room, but there are no rules about what you can and can't ask about here.

kauray

Anyway, m just starting off fresh, so will be having plenty of questions i guess

user434058

4:48 PM

@JohnRennie BTW what's your highest score in that game?

Loong

5:04 PM

So, I tested my self-made hand disinfectant today at work and my hands didn't fall off.

Also, our canteen is open again. :-)

Slereah

@Loong You're moonshining?

Loong

Mar 30 at 8:52, by Loong

and I need cocktail umbrellas

Yuvraj Singh...

@loong is lab is still open?

Loong

5:19 PM

Both laboratories are open, sure.

Yuvraj Singh...

Wow!

user434058

6:58 PM

Flags finished $\Rightarrow$ Day finished. Good night!

Manas Dogra

9:33 PM

Angular momentum of ground state electron in Hydrogen atom=$\hbar$(Bohr model)

Angular momentum of ground state electron in H atom=0(Non relativistic quantum mechanics)

How to reconcile?...Is Bohr's model simply giving wrong answers here because its semi-classical?

ACuriousMind

Yes.

Manas Dogra

Can I ask you another question on quantum mechanics,please?

ACuriousMind

As the room description says: Don't ask about asking, just ask.

Manas Dogra

In quantum mechanics,qualitative analysis and sketching of wave functions from given potential,A rule is to have High probability amplitude in places of high potential,since kinetic energy is low there-->velocity is low too...,so the particle spends more time there,and probability amplitude increases.

But a particle tends to be in the minimum potential regions too..
How can we reconcile this?

In fact,the Harmonic potential ground state follows this-"a particle tends to be in the minimum potential regions too.."

and the 1st excited state follows the potential directly proportional to amplitude thing

ACuriousMind

I have never heard of this rule, I'm afraid. There's infinitely many different possible wavefunctions, what state exactly are you trying to draw with that rule?

Manas Dogra

9:47 PM

https://physics.stackexchange.com/questions/116340/quick-question-on-sketching-wavefunction-in-well

The first answer,gives this rule apart from a bunch of documents and lectures..

I am just trying to figure out the nature of the amplitude...of any eigenfunction...
I know the number of nodes and frequency dependence thing.
In fact the question-asker's solution manual gives probability amplitude high in low potential regions,but Emilio Pisanty has given proper reasoning to say exactly the same...

nitsua60

It sounds like you're drawing an equivalence (or at least a one-to-one correspondence) between amplitude and energy, but I'm not sure that's reasonable.

(For a wave function, obviously.)

Manas Dogra

@nitsua60 I thought so too,but then i saw this

ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2016/…

and this
https://physics.weber.edu/schroeder/quantum/Qualitative.pdf

ACuriousMind

@ManasDogra The heuristic Emilio gives there is just for such step potentials

For anything else, like the harmonic oscillator, you just have to solve the Schrödinger equation

You can't just expect to be able to sketch the eigenstates for an arbitrary potential without doing that

Manas Dogra

@ACuriousMind So,restricting to step potentials,What Emilio said was correct or the other one?Because the other option is also given in some books,and "low potential,particle wants to be there,we will find the particle more there!",this just sounds nice!But can't even put the other option out..

ACuriousMind

10:03 PM

@ManasDogra This heuristic is correct when the WKB approximation is a good approximation, as this answer shows.

Manas Dogra

Thank you,Sir.

JohnnyApplesauce

I don't like wasting food so...
What happens if you soak a cloth in a viscous liquid like honey?

Manas Dogra

10:27 PM

Any good book on Infeld-Hull factorization method containing example problems?

tpg2114

@JohnnyApplesauce The cloth gets covered in the viscous liquid, such as honey?

JohnnyApplesauce

I've never seen a cloth soaked in something more viscous than blood, and blood isn't that thick.

Let me get into the specifics before I try your patience again

tpg2114

It's been a long day of telecons, my patience was tried before I got here ;)

Heh

JohnnyApplesauce

- Does the cloth become less pliable?
- Is it more or less easy than water to squeeze out?
- I know from getting small dabs of honey on cloth shirts that it's very stubborn to staying unless you wash it through with water; what makes it stay?

Manas Dogra

11:44 PM

Does anybody here know who discovered holes(charge carriers)in electronics?

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