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00:46
@Jasper ...2?
@0ßelö7 Well, I count that as 3, lol.
@Jasper You're aware a monitor doesn't constitute a computer, right?
@BernardoMeurer Yes, I think we need to count the CPU, lol.
No, you can have a workstation with 2 CPUs and it's still one computer
Oh, this gets interesting.
So how do we really count the number? lol
00:59
I think counting motherboards is easy
But even that can not be true
One can argue that a supercomputer is one computer, although it has hundreds of distinct separate motherboards and CPUs
Hmm, the plot thickens.
So do you have a good definition then for the number we seek?
I'd say a computer is a set of hardware that performs computations with some degree on unity
Hmm and you probably need to add come constraints for that to make sense
I see.
Anyway, I am going to sleep, so I will see you guys in my dreams, lol.
Anonymous
01:36
@0ßelö7 Sounds like a brilliant idea to warm your feet and kill your PC. Two birds with one stone. :P
02:14
@Phase yes
for a certain interpretation of all of those words, somewhat
@BernardoMeurer $\oplus$
 
2 hours later…
04:10
Hi! actually we have $\frac{v}{c } << 1$ and have to prove $K << m_{0}c^2$,tried asking in maths chat room perhaps I should try here
04:26
@0ßelö7 You joke, but I used to use my server for ripening fruit. Even in winter if I put the fruit bowl on top of the server it would keep the fruit warm enough to ripen it in a few days.
Sadly, a couple of years ago I bought a newer more efficient server and it doesn't produce enough heat to ripen the fruit. Though on the plus side it did halve my electricity bills :-)
@BAYMAX what is $K$?
user228700
Hi, everyone! :-)
Sorry I forgot to mention, $K$ is Kinetic energy of the moving particle, so we have to prove that when $\frac{v}{c}<<1$ then Kinetic energy o the moving particle is $<< m_{0}c^2$ @JohnRennie
user228700
My name is Kaumudi and I am screwed for my Physics exam is tomorrow and I understand horse crap! ::Whistles::
@Kaumudi.H hi
if you remember me
user228700
Oh, huh, I'm sorry, I'm afraid I can't seem to... :-/
Anonymous
04:31
@Kaumudi.H Dump physics. You're going to be a neuroscientist :P
user228700
Oh! Hi! :-) You've a new profile!
@Blue delete :)
user228700
@Blue Sadly, I must pass :-(
@Kaumudi.H: Morning. As it happens I know lots about horse crap since I used to work at a stables when I was a teenager.
user228700
Very funny indeed.
04:33
physics schmysics
It's true. I was a keen rider in those days.
@JohnRennie AHA
So it was a horse, not a sheep
Horses are too tall. You'd have to stand on a stool.
user228700
Wow.
JRHNBR
I know you know what that means @JohnRennie
04:34
Heya
@0ßelö7 lol
user228700
Yellow! :-)
did you mean yolo
user228700
@JohnRennie Wow, this I didn't know!
user228700
@BalarkaSen No, that is a variant of "Hello" :-P
rhetorical question
user228700
04:36
And now I must go out to buy food, even though I am running short on time. So, so, screwed. ::Whistles as she runs out in a panic::
@0ßelö7 actually I don't. JR Has No B- R- ??
user228700
@BalarkaSen Ah. Sorry :-P
"it's just a prank bro"
@JohnRennie just the right height, no bucked required
Ah :-)
Oh my, now I wish I hadn't Googled that!!
@BAYMAX isn't that pretty trivial to prove?
04:41
I forgot , it has been long since I was in touch with relativity@JohnRennie , any link or help?
Well start with the expression for the total energy: $$E^2 = p^2c^2 + m^2c^4 $$
Where $p$ is the relativistic momentum $p = \gamma m v$
I see
Write the expression for $E$ and expand the square root using the binomial theorem.
You'll end up with $$E = mc^2 + O(\frac{v}{c})$$
In fact I'm pretty certain I did this in an answer on the site, though searching for it is going to be tricky
$E^2 = m^2c^2 (\frac{v^2}{1 - \frac{v^2}{c^2}} + c^2)$
$E^2 = m^2c^2(v^2(1+\frac{v^2}{c^2}+\frac{v^4}{c^4}+... )+ c^2)$
$E^2 \approx m^2c^2v^2 + m^2c^4$
$E^2 \approx m^2 c^2(v^2 + c^2)$
$E^2 \approx m^2 c^4 (1 + \frac{v^2}{c^2})$
$E^2 \approx m_{0}^2 c^4 (1 + \frac{v^2}{c^2})$
$(m = m_0{})$
@JohnRennie
That looks fine. When you square root both sides the $(1+v^2/c^2)^{1/2}$ expands to $1 + \tfrac{1}{2}v^2/c^2$
You could have done it more directly. Write $$E^2 = m^2c^4\left(1 + \frac{v^2}{c^2 - v^2}\right)$$ and square root both sides then expand and you get the result in one step.
user228700
04:59
@JohnRennie Same :-(
The Internet can be a scary place :-)
user228700
Indeed.
user228700
It rained exactly when I went out, BTW, and I got wet :-( Ah, my luck!
Is the physics exam really that intimidating? You seemed to pick up the DSHO stuff faster than I could type it so I wonder if the outlook is as bad as you fear ...
oh i remember jrhnbr lol
took some time, that one
05:02
@Kaumudi.H my mother used to say You're not soluble. You won't dissolve. :-)
user228700
Hang on, eating.
At least the rain is warm in Kerala!!
@Kaumudi.H Bread? Nutella? Your room mate?
2
user228700
x'D
user228700
Two pieces of cake (w/ nutella) and a veg. sandwich!
So $K = E_{0} - m_{0}c^2 =m_{0}c^2 \frac{v^2}{2c^2}$
$K << m_{0}c^2$
@JohnRennie
05:08
@BAYMAX Yes, that looks fine.
Nice! thank you @JohnRennie
hi @rob
rob
rob
@DavidZ Greetings. How's things?
Good, still busy... thankfully I concluded an apartment search today
rob
rob
@DavidZ Moving?
05:14
Yeah, or I guess already moved, for the most part - the apartment search was the last big thing hanging over my head
i.e. I collected the keys and got access to the place today
rob
rob
Best of luck to you in your new place, then.
user228700
@JohnR: That was a surprisingly nice meal!
@rob thanks. It looks really nice
rob
rob
Will you invite hbar over for a housewarming party?
@Kaumudi.H You ate cake with Nutella and you're surprised it tasted good? :-)
though I might have added cream for the ultra orgiastic experience ...
05:17
@rob hehe I don't think we'd all fit... unless you mean virtually, in which case there's no internet access yet (but that'll be easy)
As for the veg sandwich, I suppose these things have to be done :-)
user228700
The "sandwich" was definitely worth its money! 9 pieces of fried cauliflower, a smidge of cheese and lettuce stuffed between two pieces of sweet hot dog buns! 20 rupees!
user228700
@JohnRennie :-P
@JohnRennie "orgiastic"?
Never heard that one before
Of or pertaining to orgies
Really? You didn't know that? Don't you go to orgies? :-)
user228700
05:19
I've decided to forgo lunch at the canteen and buy that sandwich on some days!
Academia has gone downhill since my day!
Actually the sandwich does sound good.
@JohnRennie I'm surprised you have to ask
lol
user228700
@JohnRennie YES!
@JohnRennie really?
Can you please be decent. There are children here
rob
rob
05:21
@LeakyNun True story: that cartoon was published a day after my PhD advisor and I had wasted an hour thinking about exactly that problem
user228700
I had a filling main course and more than enough dessert for Rs. 40! That's less than 1 dollar!
@LeakyNun if you're trying to conceal the fact you're DHMO that was a bit of a give-away. And with two mods in the room! :-)
@JohnRennie :c
@0ßelö7 oh. Yeah, I forgot, I replied because that message kind of stuck out to me.
user228700
@0ßelö7 Who, who are these children of which you speak?
05:22
@Kaumudi.H me! Mental age counts!
@Kaumudi.H you
user228700
@0ßelö7 And you?
Nope
I pay taxes
user228700
Well, I'm 18.
rob
rob
@0ßelö7 My children pay taxes.
user228700
05:23
@JohnRennie :-)
@rob you must be very proud
rob
rob
"Daddy tax": one bite of whatever you're eating, especially dessert
Everyone is liable to tax. It's just that children don't usually have a high income.
rob
rob
Early protest: "no, not a single Daddy tack"
@rob an hour :o
user228700
05:24
@JohnRennie It is, it is quite intimidating. I have 8 hours to go and 20 topics to cover. Screwed is an understatement, really.
@DavidZ wot?
@0ßelö7 I'm needling John about talking about orgies in the chat
(or related things)
@Kaumudi.H well everyone will be in the same boat.
user228700
x'D Yes, that is true.
I don't get what you're remembering
user228700
05:25
Alright, then, I'm off to tackle 'em all! (I will lurk. All day long)
What have you got to cover?
Everything except the DSHO presumably?
user228700
Nope, no, even that!
user228700
I don't think that I will be awarded marks if I go about it in ways other than the specific method mentioned in the textbook.
@Kaumudi.H laaaaame
user228700
Yeah.
05:28
Seriously, what is with your school's middle school mentality
You need to put these professors on the spot
user228700
@0ßelö7 The profs. correcting our papers won't be from the same dept. and will be using an answer key specific to the reference textbooks.
@rob Yuri knows I don't pay attention in his class
user228700
@JohnRennie I'd upload a picture of my list but it would take too long :-(
@rob he scowls at me when he hands me the attendance sheet
@JohnRennie I'm having Linux problems
user228700
05:30
@JohnR: If you eventually hear pings from Hangouts, that would be a picture of the list.
@Kaumudi.H from the textbook? Oh dear...
user228700
And now, I really must do something about my situation!
rob
rob
@0ßelö7 That's nothing, I'm not even paying attention in chat.
@BernardoMeurer either use disinfectant and a wire brush or install Windows. Whichever is least painful.
rob
rob
I'm posting from the world's least comfortable chair
05:31
@Kaumudi.H I'll keep an ear open ...
@rob why are you in an uncomfortable chair?
@JohnRennie Pretty sure colonoscopy is better than installing Windows
Windows is great
@BernardoMeurer I have only ever experienced one of those two :-)
@JohnRennie is a colonoscopy not standard procedure in the U.K. when one is your age?
rob
rob
05:33
@0ßelö7 Hospital recliner. My wife had a complicated hysterectomy Friday. Probably two more nights here.
@0ßelö7 That's a good question, and I have to concede it shows one of the pitfalls of a (cash strapped) national health system.
@rob Oh no, how is she?
@JohnRennie +1 for anarcho capitalism
@rob yikes, sorry to hear that
rob
rob
@BernardoMeurer Improving, thanks.
@0ßelö7 In theory routine colonoscopies at age 50 would save lives because it would spot early signs of cancer. In practice the NHS simply can't afford to do it.
05:35
@JohnRennie yeah, and you're a couple decades beyond that :/
Though you would get a (free) examination if there were any reason to suspect you might be at risk of colon cancer.
And of course I could pay a private clinic if I were worried about it (which I'm not).
Anonymous
@Kaumudi.H Wut...
Anonymous
Answer key?
@0ßelö7 :-) Not quite!
Anonymous
Is it an MCQ test?
05:37
I would offer my services for free but the plane ticket would be unfree
@rob My prayers would be with her if I prayed, which is why I have already texted my grandmother asking for prayers!
@Blue serious question, do Indians love acronyms and abbreviations?
Anonymous
@0ßelö7 By "service" you mean colonoscopy ? :P
rob
rob
@BernardoMeurer That's very kind. Thanks.
Anonymous
@0ßelö7 ofdd
05:38
@Blue come again?
@rob Hope she recovers well :)
@Blue I mean whatever @JohnRennie wants me to do 😇
Anonymous
@0ßelö7 of course dey do (dey not only luv abbvn's bt also wrng spllngs)
Gotta sleep, cheers
@Blue you're an awful troll
Anonymous
@0ßelö7 I'm just following your foot-steps, master.
Anonymous
05:40
;)
Anonymous
@0ßelö7 Goodnight
@0ßelö7 I would get suspended for posting the obvious response to that :-)
user228700
Wokay, I return with a very important question I need answered to move on in this chapter! Do help if possible _/\_
Anonymous
Go on
user228700
::Uploading photo::
user228700
05:54
user228700
Praise the Lord!
user228700
Right, my question is this: I derived the path length to be $2\mu t\cos r$ in another case, in which the two glass plates were parallel.
user228700
I don't understand why the same may be used here.
Anonymous
Basically one part of the incident beam travels an extra optical path of $2\mu t \cos(r)$
user228700
Right, how?
06:01
What is $r$?
Anonymous
@Kaumudi.H What happens when a light beam is incident on upper surface of film shaped wedge wedge?
user228700
@JohnRennie $r$ is the angle of refraction.
Anonymous
A part of it gets reflected and a part of it gets transmitted. Right?
user228700
@Blue Well, some of it bounces back and the rest refracts through to the other medium.
user228700
Right.
06:02
Aha! And we're assuming refraction can be ignored since the light is approximately normal.
user228700
Approximately normal?!
So on effect it's like two parallel plates with normal incidence.
@Kaumudi.H $\theta$ is small.
user228700
@JohnRennie I don't understand this.
Anonymous
The part which gets transmitted again reflects partly from the bottom surface again.
@Kaumudi.H $i = \theta$. Yes?
Anonymous
06:04
When light travels from optically rarer medium to denser it has a path of $\lambda/2$ added to it
($i$ = angle of incidence)
user228700
@Blue: Dude, I understand the workings of it, what I don't understand are the assumptions made.
Anonymous
@Kaumudi.H JR mentioned the assumption
user228700
And the Math.
user228700
@Blue Right, I don't understand it. Hang on.
06:05
1 min ago, by John Rennie
@Kaumudi.H $i = \theta$. Yes?
Anonymous
If you want we can derive it without making any assumptions. But you'll get a slightly different formula.
user228700
@JohnRennie Yep! (Sorry about the delay)
@Kaumudi.H And $\theta$ is small so $i$ is small. And if $i$ is small then $r$ is also small.
user228700
Right.
And if $r$ is small then $\cos r \approx 1$.
user228700
06:09
Right, and we use the formula I derived for a glass slab because..?
The point is that in the limit of $\theta \to 0$ you get parallel plates. If $\theta$ is small then you get nearly parallel plates so the parallel plate formula still approximately applies.
user228700
Hmm, but I didn't derive that formula for a pair of parallel plates; that was a glass slab!
user228700
No air in b/w, you see.
Oops, parallel surfaces ...
user228700
Right, but my point still holds; those two setups are different from each other in that there is air in b/w but we're still using the same formula derived for one of them for both!
06:11
If the thickness of a film is $t$ the path length is $\mu t$ and for light that crosses the film twice it's $2\mu t$.
With two parallel plates the formula is the same but $\mu=1$ because the air between the plates has refractive index equal to one.
user228700
@JohnRennie OK, you're generalizing it, nice. Where's the $\cos r$ coming from, then?
user228700
Ah.
@Kaumudi.H I'd have to draw a diagram, which I don't have time to do since I have to start work, but since the light isn't normally incident on the top plate there will be some refraction. We're just saying that the effect of the refraction is too small to worry about.
user228700
No, yes, I understand it now!!
user228700
THANKS, guys! _/\_
user228700
06:15
Ah, if only my teacher knew half the things you do.
user228700
OK, I have one more question: the light ray reflected at the top glass plate, it too has a path difference of $\lambda/2$, no?
user228700
(Since it is being reflected at the glass surface, which is optically denser than its own medium, air)
It isn't a glass plate remember, it's a solid glass wedge.
Anonymous
@Kaumudi.H Yes, there are many intricacies here which your book skipped. We neglect the reflection from top surface of upper plate. (Experimental reason: Reflection coefficient for that surface is low and also that upper plate is very thin)
Anonymous
@JohnRennie It's an air wedge
Anonymous
06:27
It's written on the heading
The top reflection is off a air-glass interface and the bottom off a glass-air interface.
Ah, OK.
Anonymous
Anonymous
In reality it should like this ^
I guess the glass plates are assumed to be infinitely thin i.e. thin compared to the wedge dimensions so they can be ignored.
user228700
@Blue YES!
Anonymous
06:29
We are considering thin air wedge, so for interference we consider reflection from bottom of top plate and top of bottom plate only.
Anonymous
Also, the reason of reflection coefficient which I mentioned above
user228700
@Blue Wait...what?
user228700
Oh, wow.
It isn't an air wedge - despite the section title.
Anonymous
Basically we consider only that interference which consists of reflected rays of maximum intensity.
Anonymous
06:31
@JohnRennie Lol. Her book is crap :P
user228700
@Blue Yes, it is in my destiny to always be prescribed terrible books.
user228700
@Blue Wow, right, I understand.
Anonymous
@Kaumudi.H I usually don't buy the books which my professors recommend till I feel that they are good enough.
Anonymous
You should try learning from MOOCs and PDF books online too. If you feel that a certain book is good enough only then you should buy it.
user228700
Ah, but like I said:
user228700
06:35
1 hour ago, by Kaumudi. H
@0ßelö7 The profs. correcting our papers won't be from the same dept. and will be using an answer key specific to the reference textbooks.
Anonymous
@Kaumudi.H My god....
Anonymous
I have no words :P
Anonymous
They treat you like school children!
user228700
@Blue Me neither. Just a ball of anger and disappointment deep inside my soul.
well definitely just suicide that
user228700
06:40
@BalarkaSen Huh?
Anonymous
@Kaumudi.H Flee from India after your UG is over. Lol. :P
Anonymous
Higher education is screwed here
user228700
^ That is the plan.
Anonymous
Only IISc, TIFR and a handful of other places are doing good research nowadays
user228700
True. There is a C.N dept. in only two good colleges (IISc and IIT Kanpur, I think) here and even there, I doubt if active research is taking place.
user228700
06:47
OK, I have another question. One of the applications of this setup is to check the planeness of a surface.
user228700
This is the paragraph describing how this is done:
user228700
> It is characterised by a particular value of $n$ (in the formula for constructive interference, $2t=(2n-1)\lambda/2$) and hence follows those parts of them film where $t$ is a constant
user228700
I have absolutely no clue what this is s'posed to mean.
Anonymous
An optical flat is an optical-grade piece of glass lapped and polished to be extremely flat on one or both sides, usually within a few tens of nanometres (billionths of a meter). They are used with a monochromatic light to determine the flatness (surface accuracy) of other surfaces, whether optical, metallic, ceramic, or otherwise, by interference. When an optical flat is placed on another surface and illuminated, the light waves reflect off both the bottom surface of the flat and the surface it is resting on. This causes a phenomenon similar to thin-film interference. The reflected waves interfere...
Anonymous
Anonymous
user228700
Wtf...
user228700
Wow, thanks, man, but I was only wondering what that particular sentence meant ::sheepish smile::
Anonymous
@Kaumudi.H Did you understand the concept behind optical flat?
Anonymous
The sentence is written badly
user228700
@Blue No, but I'm not prepared to spend 15 minutes understanding it :-( I cannot, for I don't have the time!
user228700
07:06
I was wondering about that particular sentence alone...
Anonymous
For certain value of $n$, you get a $t$. If $t$ is constant...
Anonymous
$t$ refers to the distance between plates
user228700
Right. If it's constant..?
Anonymous
@Kaumudi.H You get a constant path difference :P
Anonymous
$2\mu t +\lambda/2$
user228700
07:11
And this is relevant because..?
Anonymous
@Kaumudi.H We are measuring the flatness of surface...for a flat surface $t$ would have to be constant...
user228700
Ah. ::Head-desk:: Thanks!
Anonymous
07:26
@Kaumudi.H What chapters do you have for the exam?
user228700
A bunch of optics and oscillations.
Anonymous
I see. Good luck. Shouldn't be too tough. :)
user228700
Oh, derivations in Oscillations are too much and my textbook is crappy. The exam won't be tough, learning will be.
user228700
Thanks :-)
user228700
08:27
@JohnR: Are you around?
user228700
Dang, you're not :-( Is anybody around?
Anonymous
Is your book being crappy again?
Anonymous
:P
user228700
:-P Well, no, I suspect that my brain is.
Anonymous
Okay?
user228700
08:30
For the equation ${\alpha}^2+2k\alpha+{{\omega}_o}^2=0$, two values of $\alpha$ arise.
Anonymous
Yes
Anonymous
So?
user228700
The goal is to substitute the value of $\alpha$ in $x=Ae^{\alpha t}$
Anonymous
Okay
Anonymous
What's the problem?
08:32
@Kaumudi.H this is the DSHO again. Yes?
user228700
My textbook has done it like this: $x=A_1e^{{\alpha}_1t}+A_2e^{{\alpha}_2t}$
user228700
@JohnRennie AH, you're here! Yes, yes it is :-/
Anonymous
Linear combination of solutions to a DE is also a solution to the DE. Probably that's what they mean.
user228700
Where ${\alpha}_1$ and ${\alpha}_2$ are the two solutions to the equation I said before.
user228700
I don't understand how they were able to write this.
08:33
The solution gives us an eqaution like $$x(t) = exp(-kt \pm i\omega t)$$
Anonymous
Anyhow, I need to go for lunch. JR will be able to help you out surely.
user228700
@Blue OK, thanks :-) Bye!
user228700
@JohnRennie Right, I remember.
Where $k$ and $\omega$ come out of the solution to the quadratic.
user228700
Yep.
user228700
08:34
What I don't understand is how they were able to substitute the value of $\alpha$ like that.
And in a differential equation any sum of solutions is also a solution.
user228700
> Any sum of solutions is also a solution
user228700
Huh.
the solutions form a vector space
closed under addition
user228700
I have no idea what that means.
user228700
08:36
Oh, it's alright, I s'pose I will take it as it is and move ahead :-/
Differential operators are linear, so $d^2/dt^2(a(t) \pm b(t)) = d^2/dt^2(a(t)) \pm d^2/dt^2(b(t))$
since y -> y'' + 2ky' + ω0^2y is a linear operator
sniped
@Kaumudi.H I'm intentionally throwing terms lol, ignore them
(x+y)'' + a(x+y)' + b(x+y) = x''+ax'+bx + y''+ay'+by
so if x and y satisfy the differential equation, so would x+y
user228700
@JohnRennie Ah, hmm.
user228700
I s'pose I understand it a little bit. It's OK, I will move on.
user228700
Thank you :-)
08:38
OK. Shout if you want to come back to it.
user228700
@JohnRennie I will :-) Or other stuff. There's lots of stuff :-P
@Kaumudi.H Ping me on Hangouts as I may not have the chat open
user228700
Wokay!
08:50
@JohnRennie Well, if it's a linear DE! Which the equation in question is...
user228700
09:21
4 page derivation. Friggin' hell.
user228700
Someone give me a medal.
Anonymous
@BalarkaSen can give you a meme instead
user228700
Lol.
user228700
Lunchtime! Bread and nutella. Sigh...
K is a normie though so maybe she'd prefer normie memes
Anonymous
09:25
I'm in between normie and hipster. Is there a name for me?
yes. proprietary malware
Anonymous
Malware is fine. I'm not proprietary. :'D
bread and nutella for lunch?
jesus christ. what kind of oddballs ship restaurants
09:41
42 things in the close queue again
In the 10 hours this UTC day has had, only a single review has happened. This isn't good
@0ßelö7 @BernardoMeurer This is beautiful
@ACuriousMind gimme a break! With fixing servers and K's revision I haven't stopped since 5 a.m.!
I'll do it now ...
@JohnRennie How dare you do your job instead of reviewing things on the site!
:-)
But first, someone is wrong on the Internet (specifically the PSE) :-)
Anonymous
@ACuriousMind An AI should be able to complete reviewing stuff in nano-seconds. You need more training. :D
09:54
Cor, 30 close votes to review!!! :-(
@Blue Oh, I can clear the close queue all on my own, but as a mod I'm not supposed to
Review is supposed to be community review, not my review.
3
user228700
@BalarkaSen -_-
user228700
@Avantgarde Yeah :-/ #LTD
Anonymous
@ACuriousMind Ah, I see. But is that a rule or is it just followed to minimize moderator intervention ?
user228700
09:56
@JohnRennie :-) <3
user228700
@Avantgarde Living The Dream, man :-P
@Avantgarde LSD (bass boost plays at the background)
@Blue It is a rule generally followed on "mature" sites where the community is supposed to be large enough to review on its own, but it's not written in stone anywhere

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