The h Bar

user228700

00:01

Ah, haha, nice!

user228700

(Y)

GPhys

00:41

@dmckee Assembled with a couple other grad students (that are vastly more experienced than me) a "1%" prototype of the "millicharge" particle detector. I didn't realize gain variances between PMTs were so high.

dmckee

OK, a silly question had me envisioning what has to be the silliest piece of NIM plug-boarding done in quite some time:

Now, you could DAC the data, smooth the output with an appropriately chosen analog filter, split the line, differentiate one half with an op-amp then perform an analog zero-crossing detection and use the output to latch the other signal (which has gone into an appropriate delay line) and finally ADC that to get your answer. I could even wire the analog part in NIM if I had a big enough cache of modules and couple of crates, but ... it would be silly. Really, quite silly. — dmckee ♦ 13 mins ago

@GPhys Yes, the gain matching step of any compound PMT-based detector is time consuming, picky, and very important.

0celóñe7

@JohnRennie need physics assistance

GPhys

our signal looks like single photoelectrons - test setup is going to be shipped to CERN with 12 cooled PMTs to be installed at an unused drainage tunnel near the CMS interaction point

I guess the idea is that after the setup is demonstrated working, then everybody involved can apply to fund the full experiment

dmckee

@GPhys Prototypes are great fun because they are small enough to understand in toto, quick enough to follow through all stages of the project, but real enough to be relevant.

You'll learn all kinds of stuff on that kind of project.

vzn

01:34

Large Hadron Collider finds 'direct evidence' of light interacting with ITSELF in physics breakthrough that confirms long-standing prediction / dailymail

↑ space-waves! theyre called LIGHT! o_O

0celóñe7

@Secret that is an awful way to think about things

0celóñe7

02:22

@rob I need someone worldly

@dmckee an experimental physicist could work

rob

@0celóñe7 I wasn't paying attention. Am I worldly?

0celóñe7

@rob paying attention to what?

you sound worldly

rob

@0celóñe7 What do you need?

0celóñe7

@rob I need to raise a monitor ~4"

what common items can I use to put it on

not books

rob

@0celóñe7 Bricks. They're cheap at hardware stores if you don't like the ones you find lying around outdoors.

0celóñe7

02:26

@rob is there a brick getting place in Knoxville

near Vol Hall preferably

rob

@0celóñe7 Lowes/Home Depot

0celóñe7

@rob I can't see myself going there at 2230

rob

@0celóñe7 This has to be done now?

0celóñe7

@rob ideally, yes

I used books for the same purpose at home

rob

@0celóñe7 Use books that you're not planning to read before you go to the hardware store tomorrow.

0celóñe7

02:29

but here I don't have books I want to prop up a monitor with

rob

Were you planning to read every book you own tonight?

0celóñe7

@rob no

rob

@0celóñe7 Problem temporarily solved

0celóñe7

@Slereah up early?

Slereah

Yep

0celóñe7

02:46

@ACuriousMind I don't have access to the dining hall any more

@Slereah what are you up to

Slereah

Working on my vidyah gehm

the boring parts

User interface

0celóñe7

my books seem to have broken this shelf in my apartment

trying to avoid it completely collapsing

@Slereah do a better job than bethesda

Slereah

Gonna be hard

I'm no UI expert and I work alone

0celóñe7

03:08

@Slereah Bethesda has no UI experts either

Slereah

Bethesda does that lazy thing where they use the same UI for both consoles and PC

Even though the UI is completely different

0celóñe7

@rob @BalarkaSen found a use for some topology books

Physics Meta

-1

Q: A new flag: "not-constructive"

Many a times, there are questions which are absolutely vague and have no meaning in them, like: If I fall from a great height, will I overcome the speed of light? Now, these are off topic questions, but there are no proper flags for this. Generally I flag this as very low quality, but many times...

Balarka Sen

03:47

@0celóñe7 angry reacts only

0celóñe7

04:00

@BalarkaSen name two books better suited to the task

Ravi Prakash

04:26

Hey, I want to know, the speed of a particle which is thrown with initial velocity u, when it's at half of it's maximum height

(it's thrown vertically upwards)

Emilio Pisanty

@RaviPrakash find the energy, get the velocity from the energy.

Ravi Prakash

I got the answer as u.

'u'

Is it correct

@EmilioPisanty I have never tried finding that way

Please show me..

Are you showing? @EmilioPisanty

I did: v = √(2gh) , put h=(u^2)/2(2g) and got v as u/√2

(earlier I did a mistake, I putted h as u^2/2g) :P

Emilio Pisanty

looks ok to me

Ravi Prakash

I also think :)

Can I ask one more thing @EmilioPisanty :)

Tell what is the acceleration of particle under projectile motion at the highest point of its trajectory

GPhys

04:41

gravity

Ravi Prakash

Yes!

Me too..

If a ball thrown up is caught by the thrower after 4 seconds then the maximum height attained by the ball will be: what?

I think it's 20 m

GPhys

Landau&Lifshitz takes up like a third of my book room and I don't even own the entire series

Ravi Prakash

@GPhys can u please answer my above question 🙏

I did: got that h = u and so h = u^2 / 2g , which gives h = 20

Am I wrong?

since for upward journey, h = 2u - 1/2•g•t^2 and for downward it's h = 1/2•g•t ^2 solving these two gives h = u, is it possible

Okay, leave these..

How many of you have given International Physics Olympiad

Abcd

05:00

@RaviPrakash gravitational acceleration

0

Q: Is steady state only a hypothetical concept?

Steady state with respect to the rod being heated from one end is the state when the temperature of each section of the rod becomes constant. Now, it's very similar to equilibrium but I wonder if it's possible to reach this state before equilibrium. If yes, how? Moreover, heat is always going t...

thermodynamics

Good morning @JohnRennie

John Rennie

Morning :-)

Slereah

06:55

Morning

skullpatrol

07:06

Mornin'

Ravi Prakash

@JohnRennie If a ball thrown up is caught by the thrower after 4 seconds then the maximum height attained by the ball will be: what?
I think it's 20 m.... Am I correct

John Rennie

Hi Ravi

Ravi Prakash

Hi John

I'm from India

John Rennie

Ignoring air resistance the trajectory is symmetric i.e. the ball spends the same time going up as it does coming down.

Ravi Prakash

Okay

Then?

That means 2 sec

John Rennie

07:09

So the ball starts with some velocity $u$ and takes 2 seconds to get the top of its trajectory at which point the velocity is zero.

Ravi Prakash

Yes

John Rennie

Then it takes 2 seconds starting with zero velocity to fall back down to the ground

Ravi Prakash

Using that idea, h = 2u - 1/2•g•t^2 and for downward it's h = 1/2•g•t ^2 solving these two gives h = u

(as for downward, u=0)

so h = u^2 / 2g , which gives h = 20m

John Rennie

Yes, the equation that relates distance to time is $$ s = ut + \tfrac{1}{2} a t^2 $$

Ravi Prakash

Yes, it's second equation of motion

John Rennie

07:12

If we just consider the downward part of the motion we know $u=0$ and $t=2$

Ravi Prakash

:) yes

John Rennie

So we get $$ s = \tfrac{1}{2}g ^2 = 2g $$

Ravi Prakash

I too put the same logic as you

Then 2u = 2g

Cancelling 2 from both sides , u = g

John Rennie

The equation that relates velocity to time is $$ v = u + at $$

Ravi Prakash

Yes

John Rennie

07:14

Again considering just the downward part of the trajectory we have $u=0$ and $t=2$ so $$ v = 2g $$

Ravi Prakash

Okay, then

Sid

It is 2g, not 20m.

John Rennie

Oops, ignore that!

Sid

Unless they have specifically asked you to take g=10.

Ravi Prakash

Yes because I take g = 10m/s²

Sid

07:18

Have they asked you to?

Ravi Prakash

No

Sid

Then, don't

Ravi Prakash

What i take the value of 'g' does it affects the final answer?

John Rennie

@RaviPrakash: it's nice to leave things like $g$ as symbols unless a question specifically asks you for a numerical result.

Sid

Not by much. But, it is just "wrong" to take g=10.

Ravi Prakash

07:21

Yes

Then, if i leave it as 'g' then what to do next ?

Sid

Because g is never 10

John Rennie

It helps you see the importance of parameters like $g$ in your equations, and it means you could in principle use the equations on other planets where the gravity is different from Earth.

Ravi Prakash

@JohnRennie Yes, i got it.... :)

Sid

@RaviPrakash well, you got your answer, right?

Ravi Prakash

What to do after i got v= 2g

In downward part of journey?

Sid

07:23

Wasn't the question about max height?

Ravi Prakash

Yes

Sid

Didn't you get the answer to be 2g?

Ravi Prakash

Yes

Sid

Cool. Hope we have been helpful. :-)

Ravi Prakash

Yes, and special thanks to @JohnRennie

John Rennie

07:28

@RaviPrakash you're welcome :-)

Sid

Anyway, I need to rush off to college. Good day all.

skullpatrol

Cya

Ravi Prakash

From where all of you are?

US

Can white holes exist?

Slereah

it is unlikely

Ravi Prakash

I think its a situation when a black hole is too massive that it brusts releasing massive amounts of energy.... (I m not sure, fully ..)

Slereah

07:41

No, that is not how white holes work

John Rennie

@RaviPrakash I'm afraid the usual science fiction descriptions of white holes are wildly inaccurate. A white hole is a theoretical object that is effectively a black hole but with time running backwards.

Slereah

I'm not 100% sure what scenario would be a white hole creation

John Rennie

However a white hole, at least the simplest type of white hole, requires the universe to have existed for an infinite time, which obviously isn't the case since the Big Bang was only 14 billion years ago.

Slereah

I suppose it would be the black hole evaporation backward

John Rennie

So it seems very unlikely that white holes actually exist.

Slereah

07:46

Which would be... positive energy flowing inward, negative energy flowing outward

Which I don't think is a likely scenario

skullpatrol

Not to mention, the possibility of all the various shades of grey holes in between :-)

Balarka Sen

08:19

is black hole a non manifold point or just like a point of singularity of the metric

what even are these shitz

Slereah

a black hole is the region inside the singularity

it's just a subset of the manifold

the singularity is part of the completion of the manifold

Balarka Sen

isee.winrar

Ravi Prakash

@JohnRennie I too agree. Do you know what incident happend in 2006 like gamma ray brust

John Rennie

@RaviPrakash you mean GRB 060614? These guys suggested it might have been a white hole but I suspect most astrophysics think this is rather fanciful.

skullpatrol

08:46

We should have a "solar eclipse" event in here, no?

Slereah

Black holes can be defines quite fancily

Ravi Prakash

@JohnRennie yes, its fanciful..... If white holes were to exist, why do they disappear after short time..

Slereah

A black hole is defined as $\mathcal{M} \setminus I^-(TIF)$

or something similar

Ravi Prakash

why we don't have mathjax here in chat?

Slereah

21

A: Any chance of MathJax in chat?

As a workaround while this request is pending, there exist several client-side workarounds that can be used to enable LaTeX rendering in chat, including: ChatJax, a set of bookmarklets by robjohn to enable dynamic MathJax support in chat. Commonly used in the Mathematics chat room. An altern...

skullpatrol

08:51

We do^ @RaviPrakash

Ravi Prakash

How @skullpatrol

skullpatrol

Click on the question.

Ravi Prakash

I did but i didn't got how to.. Help me

Balarka Sen

instructions are given here: math.ucla.edu/~robjohn/math/mathjax.html

skullpatrol

Those are the best instructions^ @RaviPrakash

Ravi Prakash

08:56

Okay

Avantgarde

10:49

"everything was solved 100 years ago
todays physicists are theorists"
How did I miss this?

Also, someone please teach me how to quote a message.

Balarka Sen

> Quote

Ok, so that works

Do "> Quote". Make sure to put in the space.

Avantgarde

> Balarka

Balarka Sen

> Rats I don't know your name

Avantgarde

No but, how do you quote it in a way that the sender's username is also displayed?

Balarka Sen

Oh, huh good question

Why not just put in a -

> Also, someone please teach me how to quote a message - Avantgarde

Avantgarde

10:55

lol not very legit :P

Balarka Sen

#simplelifehacks

Avantgarde

Don't believe everything you read on the internet - Newton

Balarka Sen

lol

Avantgarde

It's everyday bro - Jake Paul

Balarka Sen

England is my city - Nick Crompton

Sid

11:10

@Avantgarde When did Newton have internet?

John Rennie

@Avantgarde you mean like this?

16 mins ago, by Avantgarde

No but, how do you quote it in a way that the sender's username is also displayed?

Sid

in The Sphinx's Lair, 8 mins ago, by Wen1now

If you put 'of the day' in front of anything, it makes it sound really important. Also, sometimes people make the assumption that you'll give more things 'of the day'.

Balarka Sen

Of the day of the day: Of the day

John Rennie

I've just bought myself this:

i.e. a giant mouse mat. And it's great.

Sid

Mouse mats are pretty good. But isn't that too big?

John Rennie

11:18

For years, decades even, it's been annoying me that mouse mats always slide around a bit when you move the mouse. But this mat is big and heavy and the weight of the keyboard holds it in place.

So, finally, I have a mouse mat that DOESN'T MOVE!

Sid

Can you move the mouse smoothly over that?

John Rennie

Yes, it's topped with fabric just like the usual small mouse mats.

skullpatrol

How much did it cost? :^)

John Rennie

£5.75

Sid

Euros or pounds?

John Rennie

11:25

Pounds sterling my good man! Pounds sterling!

We Brits don't use Euros!

Though the way the exchange rate is falling any day now the pound will only be worth one Euro.

Sid

It is close to 1 Euro, no?

John Rennie

CooperCape

Anyone else from UK get A/AS grades today? :/

John Rennie

It was worth 1.4 Euros before Brexit!

skullpatrol

That's a good deal with the 6 month warranty.

Sid

11:28

The pound was strong during mid-2015. It has been falling freely since.

John Rennie

Whether a six month warranty on a mouse mat is worth anything is debatable. It's not as though it has any parts that could go wrong.

£5.75 is probably quite a lot by Indian standards, but I bet if you were buying it in India it would be a lot cheaper.

0celóñe7

@JohnRennie never heard back from you...

John Rennie

@0celóñe7 what did I miss?

0celóñe7

I have a shelf above my desk that might collapse

I need to know how to know

John Rennie

How to know whether it will collapse?

0celóñe7

11:39

Yes

It makes some creaking noises

I had it full of books

Then I removed half

It still made noises

John Rennie

I doubt it's possible to predict a collapse. You'd need to know the strengths of all the joints and the only way to measure those would be to stress it to the point where it fails, in which case the point is moot.

Work out the largest weight you're every likely to put on it, then load it to double that weight. If it survives you should be fine. If it fails you're down one bookcase but at least it didn't fail when you had something fragile and valuable on it.

0celóñe7

If it breaks I will get charged for it

I'm not worried about what's on it, but my monitors are right below

John Rennie

@0celóñe7 I bet the amount you'd be charged for the books case would be a lot less than cost of replacing your broken monitors!

You could try moaning at the landlord to fix the shelf.

Anonymous

@CooperCape I don't think we've any A level guy here other than you. Have been seeing a lot of FB posts about this since yesterday.

Anonymous

@0celóñe7 Just empty the shelf (?)

Anonymous

11:50

Why take risk...

CooperCape

Oh damn... I only had one AS anyway 'cause we've kind of given up on doing AS exams now...

0celóñe7

@Blue cuz it looked nice with books up there

Ridiculous that it seemed to be unstable only half filled

Anonymous

@0celóñe7 lel.

Anonymous

:D

Anonymous

It will look worse if it breaks :P

Anonymous

11:52

Now that I'm taking carpentry classes I think I can easily fix broken shelves. Hehe

0celóñe7

This thing looks pretty stable though

I'm surprised the books were an issue

I guess I can put more on my actual bookshelf...

Anonymous

Just learnt the derivation of HUP. Feeling great! :D Oh my dear Cauchy Schwarz :)

0celóñe7

I guess this works too

quick book access

Anonymous

I keep my books on a sofa beside me. Too lazy to walk up to the shelf

0celóñe7

@JohnRennie does this count as cable gore?

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