- Видео 26
- Просмотров 50 140
Fisika Lectures
Италия
Добавлен 21 фев 2017
Welcome to Fisika Lectures, by Andrea Kouta Dagnino.
This is a youtube channel where i post lectures on Physics and Mathematics at an advanced undergraduate to graduate level.
I discuss all ranges of topics, from statistical physics to quantum field theory. Videos on topics are collected into playlists which you can find on the "Playlist" tab.
This is a youtube channel where i post lectures on Physics and Mathematics at an advanced undergraduate to graduate level.
I discuss all ranges of topics, from statistical physics to quantum field theory. Videos on topics are collected into playlists which you can find on the "Playlist" tab.
Видео
Bose Einstein condensate in ideal Bose gas (part 2)
Просмотров 3612 года назад
In this two-part lecture we discuss the Bose-Einstein condensation in the ideal Bose gas. We begin by reviewing the what we said in the first part. We then calculate the pressure for the Bose gas and see that it takes the same form in both the condensate and non-condensate regime, reasoning that the ground state gives no pressure contribution. We then calculate the specific heat by calculating ...
Bose Einstein condensate in ideal Bose gas (part 1)
Просмотров 8532 года назад
In this two-part lecture we discuss the Bose-Einstein condensation in the ideal Bose gas. We begin by reviewing the basics of Bose-Einstein statistics and conceive a thought experiment where we lower the temperature of a Bose gas keeping density constant. This leads us to the ridiculous conclusion that the temperature of the gas cannot be lowered further than a critical temperature. Finally we ...
The Fermi-Dirac gas
Просмотров 6412 года назад
In this lecture I discuss the Fermi-Dirac gas. I begin by expressing important thermodynamic quantities as integrals using the concept of density of states. I then develop the theory of Fermi-Dirac integrals and show how they are equivalent to the polylogarithm function. Finally, I use these functions to derive closed form expressions for the number of particles, pressure and internal energy, a...
The Sommerfield approximation for Fermi-Dirac gases
Просмотров 1872 года назад
In this lecture I derive the Sommerfield approximation for Fermi-Dirac gases. This is a low temperature approximation for the Fermi-Dirac integrals which are extremely useful to express thermodynamic quantities given as polylogarithmic functions in the low temperature limit.
Bose Einstein condensation - harmonic trap
Просмотров 1 тыс.2 года назад
In this lecture I discuss Bose-Einstein condensation in a system of bosons in a harmonic trap, deriving the critical temperature of this phase transition.
Scattering off a spherical well
Просмотров 4352 года назад
In this lecture we calculate the phase shift for s-wave scattering off a spherical well potential using a partial wave expansion.
Special Relativity and Electromagnetism (part 1)
Просмотров 1,2 тыс.3 года назад
In this two-part series of lectures we explore the special connection between special relativity and electromagnetism. In part 1 we revise our knowledge of classical electromagnetism, discussing the transformation law of charge and current densities, the gauge invariance of Maxwell's equations and the Lorentz gauge.
Loss of simultaneity (train thought experiment)
Просмотров 5153 года назад
In this lecture I give a visual depiction of the loss of simultaneity in special relativity using Einstein's train thought experiment. Here is the interactive desmos plot that you can play around with: www.desmos.com/calculator/5ichykl4be.
Solving problems in the Canonical ensemble
Просмотров 2,3 тыс.3 года назад
In this lecture I derive in detail the fundamental relations between the partition function and various thermodynamic variables, such as free energy, internal energy, entropy.
Quantizing the EM Field
Просмотров 8 тыс.3 года назад
In this lecture we quantize the electromagnetic field in second quantization, using notions from Fourier analysis. Lecture notes: drive.google.com/file/d/1Vsos1m-T1yCJTqYyuzZ0XxNA-D74kzCt/view?usp=sharing
Deriving the canonical ensemble (gibbs entropy)
Просмотров 3,2 тыс.3 года назад
Deriving the canonical ensemble (gibbs entropy)
Deriving the Canonical Ensemble (boltzmann entropy)
Просмотров 8 тыс.3 года назад
Statistical physics lecture course In this video we derive the canonical ensemble using the boltzmann definition of entropy. Lecture notes at
L1.7 Vector spaces vs vector subspaces
Просмотров 994 года назад
Course in Linear Algebra Lecture 7 - Vector spaces vs vector subspaces
L1.5 How to prove that a subset is a subspace.
Просмотров 1,7 тыс.4 года назад
L1.5 How to prove that a subset is a subspace.
L1.6 Direct Sums + DIFFICULT example on function spaces
Просмотров 3314 года назад
L1.6 Direct Sums DIFFICULT example on function spaces
L1.3 Proving a Set is a Vector Space
Просмотров 18 тыс.4 года назад
L1.3 Proving a Set is a Vector Space
5.6 Example 2: line integral of non-conservative field
Просмотров 1564 года назад
5.6 Example 2: line integral of non-conservative field
5.5 Example 1: Work and Line Integrals of Conservative fields
Просмотров 644 года назад
5.5 Example 1: Work and Line Integrals of Conservative fields
5.3 The Generalised Work Energy Theorem
Просмотров 1334 года назад
5.3 The Generalised Work Energy Theorem
Another question regards the following: U are explaining the description of a field in a box with the boundary condition saying that it disappears on the box walls. It is obvious, that only some wafe-lenghts are allowed here, which U may call quanta. But is a free field without any box quantized too ?
Actually U explain the quantisation demanding nonvanishing commutator [p, q] from the Quantum Mechanics. This means your explanation says - why is EM field quantised ? - Well, beceause it is quantised in QM. This have a rather low explanation value, I am affraid. I seems to be only an adequate descripion and nothing more. We still do not know, why is EM field quantised.
Nice explanation, but why do U have an both expenents =/- i(kr - wt) ? If time increases r increases too, so both parts are running forward. Is't it neccessary to put one exponent (kr + wt) to have one part running backwords ?
Is this applicable to antennas in telecommunications? I believe this is mostly for research applications with phd or doctorate level. Just curious but very well explained.subs and liked🎉🎉
simple and easy to follow :)
Hey. Are you sure about the signs in the (Euclidean) Lagrangian? Most texts have a relative negative sign between the two terms, i.e. L = - ( + <n|∂/∂τ|n> - <n|H|n> ). I was also following your derivation, and I feel that the error might have crept in at the timestamp 22:19, where you approximate <n_{j+1}|n_{j}>. The way I calculate it is as follows - |n_{j+1}> = |n_{τ+ε}> = |n_τ> + ε . ∂/∂τ|n_τ> => <n_{j}|n_{j+1}> = <n_τ | n_τ> + ε . <n_τ | ∂/∂τ |n_τ> = 1 "+" ε <n_τ | (∂/∂τ |n_τ>) And ofcourse, we need to take a complex conjugate to get <n_{j+1}|n_{j}>, which only switches the state on which the derivative acts <n_{j + 1} | n_{j}> = 1 "+" ε <∂/∂τ n_τ |n_τ> The highlighted "+" above seems to be the source of discrepancy to me.
리만 아티야 내쉬는 리만가설을 풀었다.
There is a type of Space-Time diagram in which the scale for both systems is the same. They are called "Loedel Palumbo Diagrams" and with them any analysis of special relativity is significantly simpler. They were developed in the mid-20th century by the Uruguayan physicist Enrique Loedel Palumbo from the simple, but brilliant idea, of considering in a diagram of Minkowski not one, but two "mobile" systems with the same speed, but in opposite directions and then remove the "fixed" system from the middle and... voila! you have two systems with the same scale! .The relative speed between these two systems is now given by the sine of the angle between the axes, not by the tangetic and trigonometry is that of all life. It is a shame that they are not very widespread.The deduction is very simple and can be found in the following link ruclips.net/video/o4kKeG8PyyM/видео.html
How can you use a non-relavistic gauge when an electromagnetic wave always travels at the speed of light. All Maxwell Equations are inherently Lorentz invariants. Indeed that is the actual original derivation of Lorentz transforms before Einstein other way in 1905.
The laws of EM can be expressed in a Lorentz covariant formalism, but that does not prevent use from choosing a gauge which breaks which "symmetry". The choice of a gauge after all has no physical interpretation, it is equivalent to choosing any other gauge.
Problems would only arise if you wanted to change frame of reference, because the gauge is not covariant, meaning that it doesn't keep the same form under Lorentz tranformation. Non-relativistc means this in this context, not that it can't describe waves moving at the speed of light, it very well does. In other reference frames, however, the Hamiltonian would be different. The result of this video, derived in the Coulomb gauge, is thus only correct in one frame of reference. But it IS correct.
I really appreciate your knowledge sharing and more impressed with your educational background. It gives me confidence to study at the OU and took a master's at renowned university.
Thank you!
Hi!Can you please elaborate on the taylor expansion?
If you upload future videos it would be useful to do small edits where mistakes are made as you did in a prior video for a missing prefactor. I wasted a few minutes working out the calculations myself several times and error-checking urs, but a few minutes later in the video you do so anyway so it was a bit of a waste of my time feeling crazy I had made an error. I've gone through this content several times over the last 5 years and I've gotten tripped out and seen others tripped up in these integrals including Kardar himself so I think it is quite common for us to make these slight housekeeping errors when manipulating these more tricky integrals.
how did you find the alpha = -2beta?
Superb video, was very helpful!!!
Nice video!
Great explanation
I believe you have defined the creation and annihilation operators incorrectly. Taking your expression for a at 39:10 and substituting in the expressions for q and p into the expression for a, I find that the final result has an additional factor of hbar. I believe that the hbar should be on the denominator in the fracrtion for the expression for the creation and annihilation operators. My maths is a bit rusty though so it's worth checking.
Could be, either way it's just a factor of hbar and in natural units that's equal to 1 so no need to worry about it too much.
@@fisikalectures597 other than that great video!
Nice video! Would it be possible for you to share the whiteboard annotations with me?
why do you not find additive inverse please reply
Excellent. You're vivid and articulate. Like your delivery style very much. I was looking for such a lecture. Thanks dude.
thanks!
Very nice and useful 👌👍👍👌
Keep going
Sorry if it's a stupid question, but why is there no contribution to E from the scalar potential (-grad V)?
Not stupid at all, I was unclear on my part and forgot to mention/took for granted that we are also working in a gauge where V=0 (this is known as a Weyl gauge). This does not impact the Coulomb gauge since the latter is only a partial gauge fixing, i.e. we can still set curl(A) = 0 in the Weyl gauge. Depending on the reference curl(A)=0 (EDIT: should be div(A)=0) and V=0 together are known as the "Coulomb gauge".
@@fisikalectures597 Thank-you for the answer! I've heard of the Weyl gauge, but I didn't understand why it was okay, and hadn't heard of the concept of a "partial gauge fixing" before - very interesting! I think you made a small typo, but I understood what you meant; div(A) = 0 instead of curl(A) = 0 (unless I'm still misunderstanding something, in which case, sorry!)
My mistake, thanks for pointing it out!
Is it not the case that he is working in vacuum and that in the absence of charge the scalar potential is always 0? This is the explanation my textbook (Advanced Quantum Mechanics by Nazarov and Danon) gives.
well technically in vacuum we don't have any sources so A = 0 and V=0. However when we refer to vacuum what we mean is there are potentials A,V produced by sources "outside" the vacuum.
This creates a huge paradox. What if each receiver has a second function. Instead of just turning on, it also disconnects the wiring of the opposite receiver. That would mean create two different alternative realities that cannot coexist. How can the lights be both on in "A's" reality, & 1 off 1 on in "B"s reality???
Great question! This generally depends on the space-time interval between the two events triggering the receivers. If the events are time-like separated then no physical Lorentz boost will ever invert their time ordering, so your thought experiment will not produce contradicting answers. If the events are space-like separated then there exist suitable Lorentz boosts that can invert the time ordering. So according to one observer one receiver lit up earlier while for the other observer the other receiver lit up. The problem is that if the receivers are space-like separated, there is no physical mechanism that can allow one to disconnect the wiring of the other, by definition. Two space-like separated events have no way to interact since not even light can pass through them. Consequently in this case your thought experiment is actually impossible to perform, even under ideal circumstances. I hope that helps!
There are some sort of questions were we need to make assumptions such as u is equal to something and v is equal to something so we can solve it. So, how I can know that I don't need to make assumptions and when I need to ?
Firstly, thanks for watching! Now to your question, let's say for example that you want to prove the additive inverse axiom, that is you want to prove that given any vector in a vector space it has an inverse such that when the two are added you get the zero vector. The way you prove this statement is by usually letting the vector u be equal to the general expression for an element of a vector space, and finding its additive inverse (and also proving that this inverse belongs to the vector space). So in general you will have to set "u equal to something" as you say when you need to prove a general property of a vector space.
Thank you, it was useful for me <3
I'm happy to know that it helped!
So for the zero vector and the additive inverse we have to find a value within the set to make the axiom true and if there is none, the set is not a vector space?
Yes, if there is no vector in the set which satisfies the zero vector axiom (or the additive inverse vector axiom) then the set doesn't have the required vector space structure.
Blessings, good work, join our Week in Review Sunday nights, and hope to do another Science of COnsciousness conference post stream today
Hey I just found your channel looking for linear algebra courses, I was wondering how making RUclips videos has helped you develop your understanding of a subject and if you recommend I persue this learning technique?
Absolutely, there's no better way of learning a subject than teaching it. Also, just wondering, what courses would you like to see on this channel? Would you prefer mathsy stuff (e..g group representation theory or fourier analysis/PDEs) or some physicsy stuff (relativistic QM or QFT etc...) Thanks for subbing btw!
@@fisikalectures597 Physics especially!
And also if you can continue youre lectures on linear algebra as they seem to have cut off suddenly 🙏
Suggestions taken!
I am searching for this type of video for some time, I found this video, at last, it cleared all my doubts thank you
that's so great to know! More vids coming soon once exams are over.
Thanks bro
No problem!
*👍😉привет от тренера по футболу!*
your a very brave guy
Awesome
Keep up with the work ! I really like physics but ive never really had the chance to study it properly in school. I only know the basics haha I like your videos ! Have a nice day ! :)
thank you so much!!! hope these videos help