Physics 27 First Law of Thermodynamics (21 of 22) Summary of the 4 Thermodynamic Processes
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- Опубліковано 24 лип 2013
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In this video I will give a summery of isobaric, isovolumetric, isothermic, and adiabatic process.
people like you are the true heroes of the world.
Thankyou so much. This video was published 10 years ago when i was i like 4th grade and u still replying to all the doubts in the comments. Absolute Lengend.
Thank you. It is great to interact with our viewers.
I’ve been stressing about my physics final all day, thank you for this
You’re welcome 😊
I've watched a lot of vdo's about interference of light, including yours vdo's: Physics - Interference of Light The Thin Film. And i passed for physics. Thank you so much.
Now i'm back for Thermodynamics.
Seriously, you're a real life hero for this video. College students everywhere are grateful.
Not a hero. Just glad my wife and I can give back a little to the world.
COLLAGE???? it’s 10th grade here in Italy. 🙃
You Tube is really helpful to us because it makes us understand things even lectures and anything you would like to research about .
Great summary! Very helpful to recap information a few days before my thermo I exam. Thank you.
God bless you man ,
"your follower from Egypt"
Samual,
The equation for delta U (change in internal energy)
is always:
delta U = n * Cv * delta T
sir, shall we use n or m?
this is the most asking question
i will remember this, no matter what happens, sun explode, my cat dying, end of the world, my bike got stolen, no more pepsi, 1/0 is defined, etc.
delta U will always be n * Cv * delta T
What is Aneroid barometer efficiency ?
Please found for shake of universe ?
∆
Thank you for these amazing classes..
This was extremely helpful , thank you so much
A really amazing and helpful video to build up the concept. Sir can you make a video on the polytropic process.
This is probably the most important video in this chapter. Thnx!
Definitely a good summary. 🙂
very simple and easy to understand thank you
Great summary, thanks!!
Cleared up a few confusions I’ve been having thank you so much
Glad it helped!
just excellent !. thanks for all the videos
Love this summary, I just copied it down, now I’m gong to go take my quiz. Thanks.
Thank you sir for your huge effort
I've been stressing over my computer skills exam all day thank you for this
Glad you found our videos. 🙂
that tie is excellent!
Thanks to Professor van Biezen, Please clarify in Isovolumetric Process,V=cte, what is de Heat Rejection in pulsejets,Lenoir cycle, Q, expression, regarding Thrust Force on 50 Hertz or cyles /sec.? Kind Considerations,Thankfully,Johann Wegmann.
love you,the great teacher............
I appriciate this channel
Thank you!
Mr Biezen, I just started thermodynamics, and your videos are really great help.I wonder if you can explain about Polytropic Process, I been taught that there are 5 processes, and polytropic process is one of them. Would be great help if you can. Thanks
Mubashir
The general equation is:
PV^n = C where C is a constant note that the ideal gas equation is:
PV = nRT
Draw the PV^n = C equation for different values of n and you'll see an interesting pattern. start with n = 0, then n = 1, n = 2, etc.
This is great!
Do you call the process of converting a solid to a liquid through a change of pressure 'melting', or is there a more precise term?
It is technically a change of phase due to the change in pressure.
Thank you so much sir
Thanks so much sir.. big greeting from iraq
Love this explanation, easy to follow
Glad you liked it.
Splendid ....
Another semester...and we are starting with thermodynamics...good work my eistein
We have a lot of videos on thermodynamics. Enjoy!
@@MichelvanBiezen Nice i will check out ✍️✍️✍️💪
Sir, please read this question. What are these red lines that you draw on the graph?
The red lines are called: "ISOTHERMS" They represent lines on the PV diagram along which the temperature remains constant. An isothermic process is drawn parallel to isotherms.
well explain sir .. thank u
At the 4:30 mark where you calculate the work done during an adiabatic process: how are you justified in stating that the volume remains constant (and hence the selection of your constant volume equation) ? I thought all 3 variables (volume, pressure, temp) are permitted to change during this process.
Chris
I did not state that the volume stays the same.
I used the equation for change in internal energy.(which uses Cv) (notice that V2 - V1 is not zero)
Excellent summary!
Thank you. Glad you liked it! 🙂
In an isochoric process how do you know the change in pressure is constant and not exponential?
That is so by definition. An isochoric process is defined as the volume changing while the pressure remains constant. W = P x delta V
thank you
very good sir van
Thanks for the clarification!!
Glad it helped.
why for p,v,t we associate the names with the change of the variables ex.(change in pressure/temp/vol = 0), but we just say heat = 0 instead of saying 0 change in entropy in the adiabatic case. is it to avoid students asking what entropy is?
No, that topic is covered at a later time. Typically we don't mention entropy yet, during the introduction to the adiabatic process.
thank u so much! ur videos are very useful!!!
Glad you like them!
The man literally saved my physics final
Glad to hear it. Good luck on your final! 🙂
Thanks a lot
Very well explained…thank you
You are welcome! Glad it was helpful.
On isothermic sir, Q = W, will it violate 2nd law of thermodynamics? Where all heat cannot be converted into work? Sorry im just confused.
No it doesn't violate the 2nd law of thermodynamics. Only the heat added is converted to work.
what is the significance of the red lines on eitherb sides of the isthermic and adiabatic P x V graphs?
The red line are isotherms (along which the temperature is constant). That way you can compare the isothermic and adiabatic process.
I'm curious,
for an Isobaric process, wouldn't Q = nCv delta T and
delta U = nCp delta T, as Cp is really Cv + R
By definition, delta U is always equal to: delta U = n Cv delta T regardless of the process
Thanks! From Ethiopia
Welcome to the channel!
Hi Sir, since you are teaching thermodynamics from the pov of Physics, I think it will be better if you describe work as "work done by the system" instead of 'by gas', because I got confused for a moment, if this was chemistry or physics. I hope I made sense and sorry if I didn't.
It is done both ways, and varies by text and author.
Do we use different sign conventions in physics thermodynamics?
In my chemistry textbook, the equation is dU=dQ+dW
In my physics textbook, the equation is dQ=dU+dW
Earlier negative sign was assigned by the work is done on the system and positive sign when the work is done by the system . this is still followed in physics books , although IUPAC has recommended the use of new sign convention..
dU = dQ + dW: The change in internal energy of the gas is equal to the heat added to gas + the work done ON the gas. dU = dQ - dW: The change in internal energy of the gas is equal to the heat added to the gas - the work done BY the gas
Hi could you tell me the relationship between the pressure and temperature in an adiabatic process please?
TV^(gamma - 1) = constant
So nice
Does anyone know why ∆U is sometimes written as equal to mC∆T and sometimes equal to nC∆T , which one is correct? Or when should either be used?
When we are dealing witn gases it should be delta U = n c delta T n = number of moles For solids and liquids we typically use m for mass (in kg)
@@MichelvanBiezen alright, I think I get it now. Thank you.
this guy is a true baller
Are you able to tell me how you practically change the volume without changing the pressure? My professor always avoided this detail. And later I found no book that looks at this question. My thoughts to this are all useless. I thought one could punch a hole in the back side so that the exess air can escape, but then this would mean that the pressure outside must be the same as inside, otherwise the volume would adapt to the outside pressure. But if the pressure outside is the same as inside, whats the point of defining a volume here?
Take a container and place a sliding lid at the top (like the piston of a car cylinder). Place a mass on top of the lid, such that the force remains constant and hence the pressure remains constant. If you heat the gas, it will expand under constant pressure.
@@MichelvanBiezen I see! Thus you do not change the volume yourself, but allow it to change when it gets heated or cooled, using a piston that excerts a constant force. Thanks, this makes it all understandable. The temperature does not change due to a change of volume but it gets changed by adding thermal energy. Thus cause and effect are reversed. Cause is the heating and effect is the volume change. Thanks!
That is correct.
Sir, how about polytropic process?
What is the question?
In Isothermal Process Change In temperature Is ZerO B/c Of Constant as We Know Q=MC Change In Temperature
So We Say temperature Is Constant For Isothermal Process Why Heat Become Zero?
pls Teacher Answer It It Confused Me A Lot
In an isothermal process, the temperature remains constant, which means that the internal energy of the gas remains the same, which means that if the gas does work, (by expanding), then this energy needed to do work must come from somewhere else (head added to the gas). Therefore W = Q (the work done by the gas is equal to the heat added to the gas).
where is polytropic process?
Polytropic processes are the general case where P*V^n = constant. n has nothing to do with the number of moles, but is called the polytropic index. It can be any number from 0 to +infinity.
All of these processes are special cases of the polytropic process.
Isobaric, n=0
Isothermal, n=1
Adiabatic/isentropic, n = k, where k is a substance-specific constant. For air and 2-atom elemental gasses, k=1.4.
Isochoric, n=infinity
for an isobaric process why can C_v be used for internal energy? I thought that was for constant volume only?
Ashley,
Yes, this is often confusing to students. The internal energy of a gas is only dependent on the temperature and Cv. The internal energy of a gas should not depend on how the gas got into that state.
But the heat added or taken out of a gas does the depend how the gas changes (via constant volume or constant pressure).
So remember, delta U = n Cv delta T.
Michel van Biezen I have always thought of it like this - constant volume means that no work is done, therefore dW = 0, and dU = dQ.
And since in this case dQ = n*Cv*dT, this also means that dU = n*Cv*dT, and thus dU = n*Cv*dT would then be true for all other processes as well.
Something like that.
Laurelindo
That is a good way of defining it.
Isovolumetric process and isochoric process , both are same thing ???
That is correct. Older text books use the term "isochoric", but newer textbooks use the term "isovolumetric"
Hi TY for this well explained video.
Just a question
Isnt delta U= W+Q
My lecturer taught like that. 🤔
It is Q + W when it is work done ON the gas and Q - W when it is work done BY the gas. The first law of thermodynamics is expressed both ways. I prefer the second way.
Yes so when work is done by the gas, the W is positive and the equation is delta U = Q - W. The minus sign is not representing the sign of W so W is still positive here. But if work is done ON the gas, then W becomes -W. delta U = Q - (-W) equals delta U = Q + W.
Superb sir!
Thank you
This is a fantastic comparison of these processes. Please verify where an "isentropic" falls amongst these.. I know that isentropic is both adiabatic and reversible, so would it be the same as the adiabatic -does the adiabatic equation for work presume reversibility ??
An isentropic process is just a special case of the adiabatic process. Therefore it would not represent a "fifth" process.
Yes, the adiabatic equation for work assumes reversibility. Adiabatic and reversible, collectively form the term isentropic. If there were irreversibility, it would mean there are inefficiencies in the change of internal energy and work done. The extreme case of an irreversible adiabatic processes, is called an isenthalpic process. The Joule-Thompson effect is an example of this.
At @5:04 how come it's Csub(v) and not Csub(p) as pressure is constant?
Yes, that is a common source of confusion. Cp only applies to the heat exchanged (Q = n Cp delta T) But regardles of the thermodymic process we always use Cv for delta U Delta U = n Cv delta T for all processes.
@@MichelvanBiezen Mm ok thank you.
NICE TO SEE YOU
Hope you like the videos. 🙂
Hi sir sorry just a question. In my textbook, there's also a statement says that in every cyclical process, heat transfer must occur from the system in order to get a net work output. But why is that? Been digging Thermodynamics lately and sometimes my brain is just slow.
Since the internal energy of the gas is the same when you end up at the state you started from, the energy needed to get the work done must come from somewhere else. (therefore the heat gained) First law of thermodynamics: change in internal energy (which = 0 for a cyclic process) = heat added - work done No heat added means no work done.
@@MichelvanBiezen Oh I get it! Thank you I understand now! Thank you!
@@MichelvanBiezen Yes but the question is saying that heat must transfer out in order to get a net work output?
In order to perform work, heat must travel into and out of the process. But more heat goes in than comes out. The difference is the work done. I suggest you watch the rest of the videos and this playlist: PHYSICS 27 FIRST LAW OF THERMODYNAMICS and PHYSICS 28 CYCLIC PROCESSES and PHYSICS 29 EFFICIENCY OF HEAT ENGINES for a good understanding of this topic
@@MichelvanBiezen Okay thank you!! Actually I already watched almost all of the videos in your suggested playlists but I will watch them again. Thank you though!
why do we use cv even when volume is changing?
okay here’s what I’m thinking: (I’m not taking thermodynamics at the moment). I think it is that “delta U = Cv delta T” is simply the definition of Cv and therefore it can be applied to any process since U is a state function. Also the ‘constant volume’ aspect of the specific heat capacity only depends on the fact that we’re dealing with gases. Assuming that these are ideal gas conditions, Cv would be the same for monatomic gases, and same for diatomic gases (though different for each category) since the only type of energy contained in it is kinetic energy, which is directly related to temperature and internal energy
The change in internal ALWAYS uses Cv.
Thanks.. ❤️🇸🇾
If work is done on the system, is it going to be negative sir
It depends on how "it" is defined. First we need to know what the "it" is. Let's define the first law of thermodynamics: The change in the internal enegy of the gas is equal to the heat added to the gas minus the work done by the gas. Using that definition, when the gas does work it is positive work and when work is done on the gas (by compressing it) it is negative work.
Where be the thermodynamics playlist
There are about 10-15 thermodynamics playlists on this channel. They can all be found easily from the home page. Let us know if you have trouble finding them.
Is the isovolumtric same as isochoric process
Yes it is. The current editions of physics textbooks now use "isovolumetric".
Great video, i love your bow tie!
Thank you! 😊
There is a typo in the thumbnail, should be a c_p (instead of c_v) for Q at the isobaric process.
Good catch. Thank you.
Thank you sir.
Most welcome
Sir, for isothermal process isn't delta Q 0 becoz delta t is 0???
In an isothermal process the internal energy remains the same (delta U = 0) since the temperature is constant. But when the gas expands, it is doing work. Since the energy cannot come from the internal energy, it must come from the heat added to the gas. Therefore work done = Q received.
@@MichelvanBiezen sir that's ok but what about the formula?Q = nCdt?? Dt is 0... pls clarify
That equation is ONLY valid for an isobaric process or an isovolumetric process, but not for an isothermic process.
Thanks a
Love from India 🇮🇳🙏 thanks sir
Welcome to the channel!
Bro but PV^5/3 is constant in adiabatic
That statement was referring to the state variable. None of the state variables are constant in an adiabatic process.
5:24 Delta U = n*Cv*delta T is ALWAYS true!
That is an approximation that Cv is independent of temperature, which is approximately true, but not completely true.
The complete formula is delta U = n*integral Cv dT, from T=Ti to T=Tf. Or: dU/dT = n*Cv
You're cool, What about ISOCHORIC processes😢
Isochoric and isovolumetric is one and the same. = constant volume The term isochoric is not used anymore in most newer textbooks.
@@MichelvanBiezen okay Engineer, I appreciate you.
Please what about "betta and kappa" coefficients for university thermodynamics, am searching for it on your playlist but seeing nothing
Are you referring to the coefficients of expansion? You need to specify what the coefficients are for..
@@MichelvanBiezen yes sir
my professor didnt need to everything sooo complicated
Once you see that commonality and the reference to PV = nRT and the first law of thermodynamics it will make sense.
What is n sir
n represents the numbers of mols of the gas
5 days left to my final physics exam
All the best on your final!
@@MichelvanBiezen thank you ❤️❤️
Reversible or irreversible process ? The most important point is missed lol😂
Hehehe ideal gas is used in thermodynamics not reactive gases lol
NOT ALL HEROES WEAR CAPES.
you are a g.
Not in the least. Just a simple man with lots of faults.
why cant my prof just teach this????
Making Soap
Not sure we are following you?
Nice bowtie
Thanks. 🙂