5:00 AM
@danielunderwood ScienceDaily is good, though it covers all fields.
Phys.org is also good.

5 hours later…
9:40 AM

10:07 AM
morning

Timothy James Scriven
Yesterday at 11:56 ·

You're aboard a spaceship and you crash land on a mysterious planet. To your suprise you discover an advanced technological civilization there.

Upon discovering the locals and resolving communication difficulties, you are asked to resolve for them an ancient dispute. You, they feel, are in an excellent position to be impartial. At first you try to decline the offer, but they are very insistent- the issue simply must be resolved one way or another.

They explain what the issue is. The juice of a certain fruit needs to be distributed between them.

Guys, I'm having problems calculating the voltage drop across a parallel circuit. Maybe Kirchhoff's voltage law (Vrise = Vdrop) is only for series?
So maybe I should consider the voltage equal everywhere in a parallel circuit?
And look at current as the changing parameter?

ЖЖЖЖЖЖ

Sorry?

that's ofr Slereah, not you
There are currently nobody in the chat so you have to wait later

10:20 AM
Kirchoff's law works for circuits in general. The sum of potentials along a loop is zero.

ok, Slreah got you covered, nvm then
Ж

If I have a battery and 3 leds in parallel, what will be the voltage drop across each led?

it will be the same voltage

So Vrise won't be equal to Vdrop here?

Is the circuit only consists of 3 identical leds in parallel connected to the battery, or it is more complicated configuration?

10:25 AM
yep
3 identical led.s

Then by kitchoff, for each loop, Vrise from battery = Vdrop for each led in each branch
so voltage has to be idetitical across the 3 leds

Ohh, so we can look at it like there are 3 serial circuits?
(for each loop)
Yep, got it.

yup, and that's why the total current triples when the leds are in parallel

And if the resistance of each of the 3 leds is the same, how the current through each led is I/3?
(according to my book)

R'=(3/R)^(-1)=R/3. V=IR' => V/R=I/3 => I=3V/R
The total current should triples

10:33 AM
My book says that the current going through each led is I/3
nvm, I'll go to eat now and come after 15 mins.

2 hours later…
12:46 PM
EXPLOISION

1 hour later…
1:53 PM
Guys, isn't weird that a resistor with the lowest resistance will dissipate more power? Why is that?
Why a resistor with for example 1kOhms will dissipate more power than a resistor with 8kOhms?

2:14 PM
0

Questions Given the function defined by: $$\oint e^{S(k,x)} \frac{\partial \ln(\frac{\int_0^\infty e^{-t} y^k dt }{ \int_0^\infty e^{-t} y^{(k-n-1)} dt})}{\partial k} dk = \frac{\partial S(n,x)}{\partial x}$$ Can this be used in the Borel summation sense for divergent series? If so, when ...

I wonder if any path integral guys can explain whether they have seen something like this before

2:36 PM
@NovaliumCompany the power is IV i.e. current times voltage. That's because voltage is defined as the energy per unit charge. So if you have a constant voltage then the more current you have flowing the greater the power. For a constant voltage the current is inversely proportional to the resistance, so the power is inversely proportional to the resistance.

Can someone help me understand Hubbard-Stratonovich transformations?
There are different choices for decoupling an interaction term such as the direct channel, cooper channel, or exchange channel. According to the book I'm reading--Altland and Simons-- you have to use physical intuition to choose the correct way to decouple the action. But what happens if you choose the wrong channel? The transformation itself should still be exact, no?

3:37 PM
@JohnRennie Ok thanks. It's kinda hard to grasp but I guess I'll just accept it. So simply said, more current means more power?

@NovaliumCompany If you have a fixed voltage then more current means more power
One of the things that trips people up is not being clear about what they are taking as fixed.
For example suppose the current was fixed (meaning the voltage was variable) then would the 1K or 8K resistor produce more power?

3:59 PM
This is something that is actually testable: a digital power supply (ie not a simple battery) can be set up in either constant voltage or constant current operation

4:38 PM
@danielunderwood Work culture matters a lot. Seriously.

This worldcup is amazing
If Brazil ducks out it'll be my favorite of all time
(Spain lost to Russia)

Seen the goals
He saved it with his knee
Shocking

It was an amazing save
I agree.
Germany, Argentina, Portugal, Spain. Next up is Brazil. Anyone else who contributes to the hype elitism?
I can't think of one.

England made it past the group stage. I was amazed.

That's who I vaguely remember was good when I paid attention to this

4:50 PM
The final is going to be something like Croatia vs Uruguay lmfao
Great game
I think Italy and Netherlands didn't qualify. lolol
I might follow this worldcup after all

@JohnRennie people actually think England can win this year

Oh next match is Brazil vs Mexico. Mexico's got Ochoa as their goalkeeper, right? That guy is fantastic

@BalarkaSen Croatia vs Denmark
Next match. Brazil's match is tomorrow

yes, but people also think the UK is better off out of the EU.
Both groups are wrong.

@Sid Ahh right

4:55 PM
Croatia is my favorite in that quarter. I trust England to mess up very soon.
The other quarter is a bit messy. Uruguay, France, Brazil, Belgium. Too many good teams to choose from

Brazil's gonna lose my dude
this is the most chaotic worldcup ever
3

Heh. Japan will turn into Inazuma Japan and win this damn world cup. :P

LOL

Dear @ACuriousMind Can you offer some insights to the question [Criterion for a Feynman loop diagram to give a finite value]
(https://physics.stackexchange.com/questions/297452/criterion-for-a-feynman-loop-diagram-to-give-a-finite-value)

@SRS I would have to look all the details up myself, and AccidentalFourierTransform has already provided the right buzzwords, so not really, I'm afraid

5:09 PM
@ACuriousMind Okay. I'll try to do some more research to improve the details.

0

I asked the question Criterion for a Feynman loop diagram to give a finite value long back. Though it wasn't poorly received, I did not get an answer yet. What can I do to improve the question? Of course, I can offer a bounty but many times it has happened that I didn't get any answer even then.

Can anyone quickly tell me if I am correct here? A yes or no would suffice.
(https://physics.stackexchange.com/questions/414597/nambu-spinor-representation-path-integral)

5:46 PM
0

I am a bit rusty on my statistics so the following may not be the most precise. Why is the range $\theta_{12}\in[31.42^o−36.05^o]$ called a $3σ$ range? Does it mean that the probability that $\theta_{12}$ lies between $31.42^o$ and $36.05^o$ is 0.9973? Yes. I have more commonly seen either ...

Anyone having any idea on this matter?

6:06 PM
@BalarkaSen you got that right pal...when a third world country can eliminate the defending champion, anything can happen.

### FIFA World Cup 2018

Any discussion related to World Cup, football (and also to que...

6:21 PM
Is it just me or is there some kind of persistent belief among some pop-sci level users that they need to understand all electromagnetic phenomena in terms of photons?
I mean, what's up with that?
Are they just trying to avoid the mathematical quagmire of classical E&M while not understanding the difficulty of describing macroscopic scale coherent behaviors in terms of QFTs?

Who knows what evil lurks in the minds of pop-sci users?

@dmckee I think it's just misapplied reductionism
Upon hearing that quantum theory is "more fundamental" than classical physics, they jump to the conclusion that therefore we should try to understand everything in terms of it

whelp, grand unification is a valid dream, no?

6:41 PM
@CupFever That's not at all what "grand unification" means.

does a persistent pop-sci level user know that?

7:05 PM
um... I am confused by relativity...
suppose two balls attract each other
by gravity
both balls are in free fall
so both is in inertial frame
suppose we can pick a frame such that we observe both frame is accelerating.
then I find it is really confusing .... how the two balls accelerate & the two balls are in inertial frames both true?

7:38 PM
@dmckee maybe the theory is confusing/ confusingly described...

Guys, I was thinking about a voltage divider with a load (= resistor) and what we can do is sum the second resistor with the load resistor (which are in parallel) and we get an equivalent one, after that we can view the system as if there was no load and no current going out of the output?

8:02 PM
@CupFever yes, and it seems it would at least explain E/M in terms of photons.

@vzn I haven't the slightest pity for people who (a) won't engage with the mathematical structure of physical theories and (b) complain that it is confusing.
Fuzzy word pictures simply can't capture the all the structure of the theory without being more confusing than the math.

@dmckee point taken, yeah, but what does E/M say about photons? photons are part of the theory.

Even Feynman had to make compromises with the masterful QED: The strange theory of light and matter.

lol this sounds a little like eat your spinach... aka shut up/ calculate...

@vzn Photons are part of the quantum picture of the theory. The classical picture is waves. Both describe exactly the same theory.

8:04 PM
@dmckee lets have this )( much sympathy when even the founders of QM describe it as confusing-at-times.

Some problems are better tackled one way, other problems the other way. A few problems are clear in both frameworks.

there are problems in physics that are bigger than textbook problems/ exercises and photons relation to E/M relates to them (the bigger ones) as Cup just pointed out.

8:22 PM
622

During the breakfast with my colleagues, a question popped into my head: What is the fastest method to cool a cup of coffee, if your only available instrument is a spoon? A qualitative answer would be nice, but if we could find a mathematical model or even better make the experiment (we don't h...

Wow!
Now that is popular science :-)

We have several household physics questions that have drawn both good answers and a lot of interest.
Consider also:
401

Other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls? I think that there should be a way to do it. But how?

(though my inner pendant want to point out that the answers tell how to determine which of a predetermined set of coins you've heard and not really how to determine the mass in a more general sense).
Also ....
224

This question is based on a discussion with a 10-year old. So if it is not clear how to interpret certain details, imagine how a 10-year old would interpret them. This 10-year old does not know about relativistic issues, so assume that we are living in a Newtonian universe. In this model, our un...

218

Four-legged chairs are by far the most common form of chair. However, only three legs are necessary to maintain stability whilst sitting on the chair. If the chair were to tilt, then with both a four-legged and three-legged chair, there is only one direction in which the chair can tilt whilst ret...

138

I have this problem from University Physics with Modern Physics (13th Edition): The inside of an oven is at a temperature of 200°C (392°F). You can put your hand in the oven without injury as long as you don't touch anything. But since the air inside the oven is also at 200°C, why isn't your ...

8:42 PM
thanks for the examples @dmckee

8:57 PM
@dmc is your baby enjoying her first world cup?

9:33 PM
Wow the first comment in the 4 legged chairs question zurifurniture.com/office/mogo-seat

lol

2 hours later…
11:36 PM
@CupFever Wait. Some people are playing soccer?
I've been hugely disengaged from sports ltely.