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Particle in a Box Part 2: Interpreting the Results 

Professor Dave Explains
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In the previous tutorial we solved the Schrödinger equation for a quantum particle in an infinite square well. This is also known as the problem of the particle in a box. But there is a lot to unpack regarding the results, enough to merit its own tutorial in fact. So let's check out the orthogonality of the wavefunctions in the solution set, fine some expectation values, and go over some other subtle points.
Script by Hèctor Mas
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1 авг 2024

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Комментарии : 104   
@noise_
@noise_ 3 года назад
I started quantum mechanics on a masters with no real background. These videos gave me so much insight, a week ago i literally barely understood what a couple of symbols meant. Now i can see all the documentation and understand everything on them. For this i can’t thank professor dave enough. Now i need all the exercises to know how to tackle them!
@zeyadahmed731
@zeyadahmed731 2 года назад
May I know in which field is your Master?
@andym.s.5231
@andym.s.5231 Год назад
@@zeyadahmed731 i guess you may not
@stringbean02
@stringbean02 4 месяца назад
I hope maybe you'll see this at some point. I'm currently in my last semester of my chemistry degree and have a research presentation coming up that will determine whether I graduate or not. My research involves synthesizing quantum dots and I was struggling to connect how the particle in a box model determines the wavelength the QDs absorb at. I could understand the model and I know that particle size determines the wavelength, but for the life of me I couldn't make them connect with the proper equations. These two videos have finally put it all together for me and I couldn't be more grateful as I have a meeting with my professor in 10 hours. Now I won't look stupid for not being able to connect the fundamental concepts the entirety of my research is based on. An absolute blessing at 2:00 in the morning.
@RengodStablord
@RengodStablord 3 года назад
This saved my butt today! Thank you so much for putting together such thorough content. I hope you are happy and healthy during these hard times.
@criskity
@criskity 3 года назад
Imagine flat earthers trying to understand this. They'd just balk and say "Math isn't real!!"
@northernskies86
@northernskies86 3 года назад
@@EdwardHowton If you're interested in learning this high-level physics and you don't have the mathematical toolbox to understand it, I highly recommend you check out Professor dave's series on math, starting from basic, elementary school math all the way up to vector calculus and linear algebra, and everything in between. But flat earthers are allergic to learning and deny everything their puny minds can't comprehend, like calculus or physics.
@frede1905
@frede1905 3 года назад
@@EdwardHowton This is nothing compared to modern physics today. It takes a lot of time and dedication to just scratch the surface of the mathematics of modern physical theories, because it's just so insanely complicated. Even general relativity is practically nothing compared to that, and it is famous for being hard to understand. It takes years and years of hard work to reach the level of mathematical literacy that these physicists have. That is why I have huge respect for those who are able to participate in developing these theories.
@frede1905
@frede1905 3 года назад
@@EdwardHowton Yes, I agree. I am more of a physics guy, and I know that I am gonna study physics after high school. Because I am so interested in it, I learn as much as possible that my brain can understand, and just this summer I tried to learn as much QM as possible. Now, something I've learned from this experience and just learning physics/mathematics in general is that everything is much easier to understand and much less intimidating once you get used to it. I mean, when you look at something, especially mathematics, for the first time, it looks extremely complicated and intimidating, but once you unpack the symbols and you start getting used to it, you realize that it's not as hard as you first think. When you read my last comment, it probably felt like these physicists are superhuman or something, but I think (and hope) that everyone can reach that level if they really want to, and if they are dedicated enough. Although the mathematics used in the most recent theories are indeed insanely complicated, I think anyone could eventually understand it if they had the dedication and time, for the reasons above. Now, that being said, I completely agree that it's insane how people can fall for something like flat earth. It doesn't even require science or math to debunk it, although it's much easier to see the insanity of their arguments if you know some basis physics. That gravity isn't real, or that water can't curve is by far the craziest of their arguments.
@thephantomeagle2
@thephantomeagle2 3 года назад
It's perfect for flat earthers since they're ZEROS.
@Diaming787
@Diaming787 3 года назад
Saying math isn't real means they aren't real themselves. They are made of quantum particles too, requiring such level of math.
@casperryde9602
@casperryde9602 Год назад
Very impressive how you can explain such difficult matter in such an easy way and using this ability to reach many people. Respect !👏👏👏
@vikasyadav495
@vikasyadav495 3 года назад
Great Video. Awaiting other complex situations - Finite well, Harmonic oscillator, etc.
@glennpearson9348
@glennpearson9348 3 года назад
Quantum mathematics made easy to understand. Also, recalling all those trigonometric identities was a fun trip down memory lane for me. Good stuff, Professor Dave! Oh, and it was nice to see a slightly different side of you on Catz's channel the other day. Take care and be safe.
@bigbrothersinnerparty297
@bigbrothersinnerparty297 3 года назад
I think it would be better to upload hard concepts like these in a row as I have to rewatch most of these videos every time since I usually forget some of what I had learned before lol. Thanks for the great videos!
@constancafigueiredo106
@constancafigueiredo106 2 года назад
Thank you so much for your videos on Quantum Mechanics. It's so easy to understand when you explain it like that
@ManojKumar-cj7oj
@ManojKumar-cj7oj 3 года назад
Please,Dave ! Add some more videos in this brilliant series
@0cgw
@0cgw 3 года назад
Great video. Another way to see that =0 is to use the symmetry x maps to a-x which preserves the system. This would send to -. But since it is the same system, we get = - so that =0. Also, =E since =0 as V is either zero or the wavefunction is.
@KrasaGalyaShararam
@KrasaGalyaShararam 2 года назад
Your videos on infinite potential box are superior! They helped me a lot. Thank you so much
@paulg444
@paulg444 Год назад
His first part was great, but this is where he really delivers !
@menglongyouk167
@menglongyouk167 3 года назад
Thank you for putting efforts into these. Appreciate it.
@IslandHermit
@IslandHermit 3 года назад
I'd always heard that quantum calculations were "difficult". After seeing this example I realize that most of the math itself is not difficult but rather the sheer amount of it required for even the simplest of problems.
@che-maticschemistrymathema7044
@che-maticschemistrymathema7044 3 года назад
I'm so happy to have a teacher like you who knows everything 😍😍😍😍😍😍😍😍😍😍😍😍😍😍, Physics, Chemistry, Biology, Astronomy................💞💞😍😍
@cguy96
@cguy96 3 года назад
Oh, he doesn't know _everything._ But he darn well makes sure he knows what he is talking about before he posts!
@che-maticschemistrymathema7044
@che-maticschemistrymathema7044 3 года назад
@@cguy96 😍😍But I see he knows almost everything.
@jesusdavidrinconpuche2193
@jesusdavidrinconpuche2193 3 года назад
I've seen this problem since 2015 and I still think it's really interesting
@hidetsuguhiraki2008
@hidetsuguhiraki2008 Год назад
Your video series are always easy to understand. In physics, we must understand what equations mean in the real world. Your video series' detailed explanation is beneficial for my study of physics. Thank you very much, Sir.
@SADI1997
@SADI1997 3 года назад
That was just Awesssoooommmmeeeeeee. Thanks a lot.....expecting more lectures
@tamojitmandal5382
@tamojitmandal5382 3 года назад
It's really beneficial for me to understand the concept of box normalization ,, again thank u
@user-qx8zg4de6p
@user-qx8zg4de6p 3 года назад
Best Video Ever
@cliffordwilliams9597
@cliffordwilliams9597 2 года назад
Thank you Professor Dave !!!
@yasminsedra7455
@yasminsedra7455 2 года назад
this is super useful! Thank you so much
@Liltommy-bz8ky
@Liltommy-bz8ky 8 месяцев назад
Thanks You just saved my life
@aymenbk9138
@aymenbk9138 3 года назад
thank you so much for this
@ManojKumar-cj7oj
@ManojKumar-cj7oj 3 года назад
Hey Dave please make one more video on this series on PARTICLE IN A RING 🤩
@eggieeeeeee
@eggieeeeeee 3 года назад
Hi professor Dave,can you please upload videos in this series (modern physics),a little quicker, as I wait eagerly for these tutorials? Love you and all your tutorials.This is just my request. Stay happy. 🤗❤
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
these are hard to make! i do them as quickly as i can. just revisit them all in a row in a few months to cement the information.
@eggieeeeeee
@eggieeeeeee 3 года назад
@@ProfessorDaveExplains Okay,thank you!😀
@ava_niche
@ava_niche 3 года назад
@@ProfessorDaveExplains Really appreciate the work you're doing
@eswarsai8293
@eswarsai8293 2 года назад
nice explanation loved it whole
@pearlsequeira3989
@pearlsequeira3989 2 года назад
😃your really good at explaining this👍 now i totally get it
@schifoso
@schifoso 3 года назад
Brilliant!
@amiraro6345
@amiraro6345 3 года назад
Thank you very much ❤️😊💕💖💖
@rowangoebel-bain3447
@rowangoebel-bain3447 Год назад
super helpful!!
@scientist1905
@scientist1905 2 года назад
Best explanation
@nasikhossain2721
@nasikhossain2721 3 года назад
Seeing ur video I am big fan of ur From India
@ilper1625
@ilper1625 2 года назад
Hi Professor. You say v can not be 0 for there is no particle. But a particle can travel exactly perpendicular to x and v(y) = v=const and then v(x)=0. Of course one has a 2d problem then, but does this change things and why? Can part of v(y) go to v(x) and why if there is not an interaction with the walls?
@ahmetg.7145
@ahmetg.7145 3 года назад
Have to work on the equations to memorize them. 🤩
@user-pk9qo1gd6r
@user-pk9qo1gd6r 3 года назад
16:30 perhaps an easier way to explain it is that the particle is constrained in a finite space so its average velocity (and thus momentum) has to be zero, and yet as we saw earlier it cannot have no energy so it has to be wobbling aroun, giving it a non zero average kinetic energy.
@coreyanderson3288
@coreyanderson3288 2 года назад
Also since kinetic energy is always positive (velocity squared) it cannot be equal to 0 if there is motion (regardless of moving in the +ve or -ve direction)
@majdiabdalla3505
@majdiabdalla3505 Год назад
Thanks
@simangcheung9420
@simangcheung9420 2 года назад
大変助かりました、ありがとうございます
@tadeletekeba13
@tadeletekeba13 3 года назад
Thank you so much prof Dave (Tadele__Ethiopia)
@amiraro6345
@amiraro6345 3 года назад
Thanks from ALX_EGYPT
@arkaeminem
@arkaeminem 3 года назад
Nice explanation... Could you make a video on harmonic oscillator by schrödinger's equation
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
yep that one is coming
@sanjayvasnani988
@sanjayvasnani988 3 года назад
@@ProfessorDaveExplains Are you still working on it? I would love it if you could continue on this series. Your videos help me understand complicated stuff easier.
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
Yes sorry! I have two more almost ready to produce and then there will be at least four more after that.
@sanjayvasnani988
@sanjayvasnani988 3 года назад
@@ProfessorDaveExplains Wow, Thanks for replying.
@michaelmurphy8736
@michaelmurphy8736 7 месяцев назад
At 16:26 why wouldn’t -psi right just be equal to psi left as typically a negative of a vector is just in the opposite direction?
@epicchocolate1866
@epicchocolate1866 3 месяца назад
These aren’t vectors, they’re wave functions, this is representing a standing wave (look up wave on a string), which is a left travelling wave and right travelling wave, these two values are not equal everywhere.
@FrostDirt
@FrostDirt 3 года назад
Have you applied for verification? It looks really weird seeing a channel this big without the mark.
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
hmm i hadn't really considered it, i'll ask my partner manager
@malehasharifi8304
@malehasharifi8304 3 года назад
Hello professor thanks for your fantastic teaching I am an ESL student but I really like to be a nurse 👩‍⚕️ and work in a medical field please help me in this way give me some advice my writing is not good I hope you know what I am saying thanks 🙏
@cliffordwilliams9597
@cliffordwilliams9597 2 года назад
@16:11 => 16:37 Mind Blown
@medicalbiochemistry_
@medicalbiochemistry_ 3 года назад
👍👍👍
@sanshou2
@sanshou2 3 года назад
Why is the last video in playlist private?
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
I will release it soon! And more after that.
@Pheosis
@Pheosis 3 года назад
@@ProfessorDaveExplains Wow, maybe it will simultaneous with my uni lectures :)
@hiesenbergw.w555
@hiesenbergw.w555 3 года назад
Hi Doc please help me I can't play your next videos Why is that?
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
Releasing them soon!
@rohanthakrar7599
@rohanthakrar7599 3 года назад
Where is the video on Bra-ket notation ?
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
a few videos back in the modern physics playlist, either the one on operators or the one after
@rohanthakrar7599
@rohanthakrar7599 3 года назад
Professor Dave Explains Thanks
@chriswinchell1570
@chriswinchell1570 2 года назад
If quantum tunneling explains radioactive decay then why doesn’t it occur in every nucleus? What is different about unstable nuclei?
@ProfessorDaveExplains
@ProfessorDaveExplains 2 года назад
Check out my tutorial on nuclear reactions. Proton/neutron ratio is off, nucleus too large, etc.
@chriswinchell1570
@chriswinchell1570 2 года назад
@@ProfessorDaveExplains Thanks.
@chriswinchell1570
@chriswinchell1570 2 года назад
@@ProfessorDaveExplains So, is it safe to say that tunneling and hence transmutation of elements is just much more likely when the nucleus is large or the ratio of protons to neutrons is unfavorable? In other words, is it that the potential to overcome is much lower than in a stable element? I.e, in theory tunneling can still occur in stable elements but the half life is very large? BTW, can half lives be calculated knowing the atomic mass number and atomic number?
@ProfessorDaveExplains
@ProfessorDaveExplains 2 года назад
I don't really know of any connection between quantum tunneling and nuclear decay. But yes, those are the reasons a nuclide would decay. Half lives aren't calculated, they're measured empirically.
@samh5550
@samh5550 3 года назад
Hey professor, would you please share with us how do you plan and make your videos and what are the equipment and software you use? you inspired a lot to think seriously to start a valuable content in our specialty field, and your advise will be very helpful. Thank you very much!
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
i use adobe after effects, it's the best! very easy to use
@samh5550
@samh5550 3 года назад
@@ProfessorDaveExplains What about the camera and microphone professor?
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
for these ones no camera, just audio. i use a crappy mic i got a radio shack for like 40 bucks forever ago, sounds surprisingly decent
@sabbitiswarender7026
@sabbitiswarender7026 3 года назад
Professor tell about life on mars
@AnimeForeLife
@AnimeForeLife 3 года назад
Yeah I'm gonna need about 3 or 4 levels of math that I dont have to follow this. I heard of the wave function, but I have no idea what the heck you're doing with it
@ProfessorDaveExplains
@ProfessorDaveExplains 3 года назад
Well this is a bit of a miniseries so start at the one on operators in quantum mechanics in my modern physics playlist to get more context. But for the math that's eluding you, visit my mathematics playlist and head towards the bottom, all the linear algebra and calculus is there for you!
@utkarshraj3272
@utkarshraj3272 8 месяцев назад
👏
@fantomphalcon9153
@fantomphalcon9153 3 года назад
“Imaginary terms” - flat earthers’ would love that, if the definition made sense to them “Yeah, complex numbers dude, J notation, -1 -using an imaginary number to solve an equation that breaks the x, y axis, y’know, complex shit” - shit, aliens have landed, but how did they get through the firmament? - We need a model........ I understood and this ‘imaginary number shit’ made it all a bad dream of quantum reality, or some shit??!
@carultch
@carultch Год назад
Pretty much. It's a name given by a critic of the concept of imaginary numbers, that leads people to believe these numbers lack any real world application.
@alaabdessayed329
@alaabdessayed329 Год назад
It hits different when u are not learning this for fun,but cz u have a national exam on it 💀
@ianlee5812
@ianlee5812 Год назад
Can't the dilemma that a particle can have nonzero energy and zero momentum be explained by Einstein's mass-energy equivalence? Since mass is proportional to energy, a particle of a finite mass will always possess some energy, regardless of its velocity and momentum?
@yufan
@yufan 2 года назад
Can n be negative?
@cafe-tomate
@cafe-tomate 2 года назад
If n is negative you get -sin then it's just the same but multiplied by the scalar (-1) And as we know the physics don't change when the wavefunction is multiplied by a scalar So considering the negative n cases is redundant (it's considering twice the same wave functions) Therefore we stick with the positive values of n Hope this helps
@carultch
@carultch Год назад
@@cafe-tomate Θανκ ιου.
@SampleroftheMultiverse
@SampleroftheMultiverse 7 месяцев назад
I have energy therefore I exist.
@wertiadreams7949
@wertiadreams7949 3 года назад
this is pretty easy to understand and I'm generally stupid
@freshely9309
@freshely9309 3 года назад
Wow the quantum world really is bizarre
@gabitheancient7664
@gabitheancient7664 2 года назад
so that's why absolute zero temperature is impossible? because a particle can't have 0 energy?
@cafe-tomate
@cafe-tomate 2 года назад
I think energy can be less than zero, if the potential goes below zero
@babarazamsucks
@babarazamsucks 3 года назад
Firs
@briefinsight4486
@briefinsight4486 3 года назад
Heart this Comment Dave or you cant do that?
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