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1:23 AM
@user586228 my bad :-). Because I couldnt comprehend those notation lol :D
@ManasDogra It looks like you are expected to identify it to be a carnot cycle
 
 
1 hour later…
2:49 AM
Please, how can I calculate a tetrad basis for a given non-diagonal metric tensor?
 
 
3 hours later…
5:38 AM
@ManasDogra I have no idea how to read F:U graphs I'm afraid. In fact I don't think I have ever seen one before you asked.
@RobinSingh Hi Robin :-)
What does angle of friction mean? Isn't friction always parallel to the surface?
@user586228 that's suspiciously close to the reciprocal of Avagadro's number ...
 
5:54 AM
@JohnRennie ncert defines is as the angle between I think Normal reaction and Frictional force
or the reciprocal
 
@RishiNandhaVanchi I must admit I have never encountered the term.
 
its really confusing where the theta i defined im scrolling through the book to see how it was defined
i dont find it useful either, its just there so they can ask us a question for one mark
 
6:16 AM
@RishiNandhaVanchi i got B , but the 3/2 is over T and not V.
 
oh yeah
I switched T and V while writing final ans for some reason
and marked B
 
maybe thats why the question is deleted.
no answer is matching
 
yeah got it thanks
 
 
1 hour later…
7:28 AM
@RobinSingh yes, what is answer given?
 
7:51 AM
@JohnRennie Sir, angle of friction is probably just a useless term. It is defined as the angle made between the normal reaction force and the resultant force of normal reaction force and friction.
@Rover Wsin(theta)
 
@RobinSingh askiitians.com/forums/Mechanics/… see second answer ...
 
Yeah I saw that already but we are given a horizontal plane in the question whereas they kept in on an inclined plane
 
8:10 AM
@RobinSingh Yes.. , then can't say anything may be ans given is incorrect.
 
Sir, maybe you have heard of Angle of Repose. I think both are same. This is angle of friction as defined by Wikipedia
@Rover I think so too
 
8:27 AM
@RobinSingh it looks to me as if W tanθ is correct.
Because tanθ = μ and the frictional force is Wμ
 
Yes sir that's what I thought too
So, the given answer is wrong?
 
@RobinSingh I'd have to see exactly what the question said to comment. Can you post a picture of the question?
 
It came in a test, the solution is kind of confusing. I think the psi is angle of incline
 
But it says the plane is horizontal, so ψ = 0°
 
8:43 AM
Yes sir, but i think they are trying to create an angle of inclination and then they calculated what is the force on the body along the incline when the body just starts to move. This should be wrong.
 
I think it's a misprint.
The question and the solution don't match.
 
Yes sir
I think so too
I think I will contact with my teacher
Thanks :-)
 
 
2 hours later…
10:59 AM
they probably assumed an angle psi between F and surface
 
11:59 AM
@JohnRennieCan you describe the analogy like you said close to the avogaro's number
Why is the analogy?
 
 
1 hour later…
1:01 PM
@RishiNandhaVanchi Just like that? F=U-TS afterall !!!
I searched all over the internet...Couldn't find even one result on it..
This one was also from TIFR...I don't understand from where these people think of these questions, and how do they expect people to do these kind of things? :(
 
1:17 PM
@ManasDogra im not aware of how F=U-TS is defined, but most of the times we are only given carnot under disguise :-)
theres another reason you cant be given WACKO processes
within a segment heat need not just be gained by the system
efficiency is defined a w/Qabsorbed. which isnt Qnet
so like say you have a straight line in PV, even if its an expansion, its would absorb some heat, emit some in between and absorb more
I believe we'll have to follow strategies like integrating along adiabatic components and stuff which gets really involving
 
@ManasDogra prnt.sc/xjudv3
It is a good idea to check if a cycle is carnot or not since we can shorten the process much faster.
@RishiNandhaVanchi Most qns I have encountered are polytropic, hopefully they don't get any crazier ideas.. . .
 
hehe lol
kvpy did have one question along these lines
ill see if I can find it
it was qualitative though
they gave a process that was a triangle in PV. options were equalities and inequalities involving efficiency
 
1:32 PM
there was an exponential type of relation in kvpy past year papers too. And truthfully I found out by integrating and got the exact exp however the approximation seemed kinda bogus
let me see if I can find that
 
the one i sent above?
23 hours ago, by RishiNandha Vanchi
user image
 
I was skimming past it they have alloted me bonus for this one
 
unofficial solutions they release for kvpy are mehhh tbh they seem to work backwards from answer key
 
is there an official solution for kvpy?
 
yeah they typoed and switched TV i think. Because we got B except T and V switched
there isnt
 
1:36 PM
@RishiNandhaVanchi that was what I remember about it.
 
I learned one thing that in kvpy u need to qualitatively attach it first lol
 
that was the qn I was talking about
I still don't get the solution though
 
do we have spoilering features here?
like ||this||
 
>! testing >!
ok nope
 
1:39 PM
prnt.sc/xjuy1n <- solution
 
im gonna first rewrite it into T and V and then see what happens at large T
might need to differentiate
wait the solution give pressure compressibility right?
we need thermal compresibility?
 
Yes you will have to do exactly that. All of it makes sense until they just left P in the last step
 
ive seen unofficial solutions go wrong
 
take a look at the solution it is a terrible amount of differentiation
@RishiNandhaVanchi :(
 
you can skip a lot of the ugliness by carefully cancelling terms in differentiation
 
1:47 PM
actually the value of compressibilty depends on the exponential of T, I just did it again
 
hopefully my mspainting is readable
at last step im put V^2/3 again
V^2/3 = c/T e^-kT
so at T-> inf you get constant compressibility
 
@RishiNandhaVanchi for compressibility we must replace $dT$ with $dP$
 
for thermal compressibility too?
wait what is thermal compressibility
 
I only know one compressibility I read in thermodynamics and that has the replacement I mentioned
and a -ve sign
 
I think you meant isothermal compressibility in question?
 
1:50 PM
it is the inverse of bulk modulus
 
ohh okok
i thought thermal compressibility was defined as dV/VdT for some reason
 
is there a term like that?
 
i googled and got none
its just me guessing term definitions because of dx memory
@napstablook and T is large
 
2:03 PM
@RishiNandhaVanchi prnt.sc/xjw32c
This was the end result of my estimation , I don't get where I went wrong :(
 
e^PV/E was in the lhs
so e^-PV/E in rhs
(speaking with respected to original equations given)
 
yep
 
uve taken in rhs guess thats where
and its not proportional to T^-2
the word proportional applies only when no other term in T is there
xe^x proportional to x is false
 
@RishiNandhaVanchi I know but the options don't even address that. . .
 
they do
when you take e^PV/E
at infinity that terms becomes really really small
 
2:08 PM
that term becomes infinitely large right? PV=RT
 
nono its not e^positive x
 
2:22 PM
oh I get it, my allen test papers have errors in it. It missed the negative in expo
 
2:32 PM
I have this doubt with how excitation states are numbered if more than one electrons are there in the system
ive been searching in google but couldnt get a lot
i get that electron at highest energy level goes to one higher -> first exitation state
dont get the second
 
@RishiNandhaVanchi I know this is a JEE chat room..but, actually this question is from postgraduate entrance exam, so you know...all kinds of things come there :)
 
I believe PHOs cover thermodynamics to this depth
there was one question which gave U in terms of S,T and something i think
some state functions like A or F which i had no idea of
 
@napstablook The definition you used is for Gibb's Free energy, not Helmholtz free energy..
@RishiNandhaVanchi Yes I remember doing that one.
 
2:47 PM
@ManasDogra and we got the same answer because it just became like U with a different coefficient
 
https://en.wikipedia.org/wiki/Boltzmann_distribution
See the equation in terms of N
 
which one?
 
@ManasDogra yeah sorry, my bad.
 
PROBABILITY RIGHT?
sorry for caps
 
2:53 PM
Yes...You get the number of particles(Ni) in ith energy state(Ei---excited or ground)...From the total number of particles(N) and background temperature(T)

This is an approximate one only though(ignoring QM properties of the electron)
 
3:39 PM
no i mean
not from a thermodynamic viewpoint
if I am told the atom Mg is at second excitation state
what state is it at
 

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