This experiment confirmed quantum energy levels

Buy me a coffee and support the channel: ko-fi.com/jkzero
In this video, we dive into the details of how the Franck-Hertz experiment provided the first direct evidence of quantized energy levels in atoms, confirming key aspects of Niels Bohr's atomic model.
[Erratum]
04:50: cos(θ) inside the square root should be sin²θ; thanks to ‪@jmmahony‬ for catching this typo.
[Related videos]
∘ Film: the Franck-Hertz experiment, Physical Science Study Committee (1961) archive.org/de...
∘ The Birth of Quantum Mechanics • The Birth of Quantum M...
∘ This effect confirmed light particles • This effect confirmed ...
∘ Millikan tests Einstein's Light Theory • Millikan tests Einstei...
∘ How Niels Bohr created the quantum atom • How Niels Bohr created...
∘ This star almost broke Bohr's atomic model • This star almost broke...
∘ Playlist video series on Quantum Physics • Quantum Mechanics
[References]
∘ J. Franck and G. Hertz, Über Zusammenstöße zwischen Elektronen und Molekülen des Quecksilberdampfes und die Ionisierungsspannung desselben, Verh. Dtsch. Phys. 16: 457 (1914)
∘ N. Bohr, On the constitution of atoms and molecules, London Edinburgh Philos. Mag. & J. Sci. 26, 151: 1 (1913) archive.org/de...
[Credits]
Heinrich Hertz, public domain
Heinrich Hertz discovering radio waves, public domain
Phillipp Lenard, public domain
Gustav Hertz, public domain
James Franck, public domain
Stanford Linear Accelerator, by P. Kaminski, public domain
Electron-proton deep inelastic scattering, by Ddn2 under CC BY-SA 3.0
Tube for Franck-Hertz experiment, by 3B Scientific amzn.to/4fDM6OZ
Hans Geiger, public domain
Ernest Marsden, public domain
Ernest Rutherford, public domain
Arthur H. Compton, public domain
Ping-pong ball, by I. Joseph free use via Pexels www.pexels.com...
Bowling ball, by A. Shvets, free use via Pexels www.pexels.com...
Franck Hertz experiment, by 老陳 under GNU Free Documentation License V1.2
Franck-Hertz experiment with neon gas, Infoczo/MikeRun as CC BY-SA 4.0
Subway station, by Sosa Films, free use via Pexels www.pexels.com...
Fluorescent lights, by KoolShooters, free use via Pexels www.pexels.com...
Tanning lamp, by D. Brown, public domain
Tanning lamp filament, by D. Brown, public domain
Franck-Hertz experiment
CC BY-SA 3.0: creativecommon...
CC BY-SA 4.0: creativecommon...

[@douglasstrother6584]

It's fascinating how much Physics was squeezed out of vacuum tubes containing various configurations of high-voltage electrodes and a variety of gasses (or a vacuum).

[@jkzero]

Totally agree, it is remarkable that the same few components cleverly arranged in different ways in tabletop experiments unveiled so much new physics over 100 years ago.

[@futureconsequence5374]

IKR! Humans are awesome!

[@anteconfig5391]

for real

[@caustinolino3687]

​@@jkzero It's also amazing how much progress has slowed since then.

[@awaitingthetrumpetcall4529]

@@futureconsequence5374 Physicists are on a different level. They used complex equations to describe what they observed. The math is way over my head.

[@novakonstant]

Best physics channel on youtube.

[@jkzero]

Thanks for that, it is very moving when viewers appreciate the content and the effort to produce it.

[@zephyrandboreas]

Beautiful and clear presentation. Amusing to see how self-deprecating James Frank was about keeping up with the literature in the field ('you know how that happens'... 😅 ). Brings memories of my Friday afternoons spent, with other colleagues, trying to catch up with the literature (when everything was in paper 😊).

[@jkzero]

Thanks for watching until the end, having that record of Franck describing his own historic experiment is just fantastic. That added to his humble and shy personality adds extra value.

[@nataliadanilov5500]

@@jkzero And modesty and shyness adorn a person.😂

[@uploadJ]

I love basic, primary experiments. Too many presenters present 'thought experiments', which have their place, but are no substitute for actual lab experimentation. Thank you Dr. Diaz for the video.

[@jkzero]

I am glad you like the content. I am totally with you, thought experiments have their place in physics, but the real magic happens with real experiments, with real measurements, and really shocking results. More of that coming soon.

[@jaredhouston4223]

This was my first time viewing one of your videos and I have to say your content looks like it took some hard work, but you obviously love what you're doing and that combination instantly made me subscribe. Thank you for this video!

[@jkzero]

Thanks for sharing, I really appreciate your kind words. Yes, it is a lot of work putting these stories to write and produce so thanks for the appreciation and welcome to the channel, make sure to check the other videos

[@Erufailon.83]

Same for me. It was my first video of this channel and as soon as it ended I liked and subscribed instantly.

[@MaximumBan]

There is a huge gap between knowing the results of the experiment and understanding why you've got these results. ❤ Epic video. Best of many science videos I saw in the last two years! 🎉🎉🎉❤❤❤

[@jkzero]

Thanks for your kind message

[@thomasgargan5971]

Hands down most amazing physics video series on youtube. I’m a second year physics student and I have never seen such a good mathematical and experimental explanation. I rarely comment on videos, but this is the best video I have seen in ~5 years of watching content like this. Please keep it up.

[@jkzero]

Wow, thank you! I really appreciate your positive feedback. I am totally with you. When I was a physics student I learned the solutions to the problems of the time but I remember that the lack of context and details was quite unsatisfactory. I decided to dig deeper, read parts of the original papers, and I decided to share the details and get the record straight. I think that the stories get even more fascinating.

[@carlosanvito]

As an electrical engineer, I can see regions of negative impedance in the experiment. Thank you for your excellent presentation.

[@jkzero]

Thanks, I am glad you like the content

[@MadScientist267]

I'm curious how this relates over to the crookes dark space in a discharge tube.

[@jkzero]

@@MadScientist267 to be honest, I didn't know about Crookes' dark space, I had to look it up. Just from a quick search, the dark spaces observed by Crookes and Faraday appear to be due to large pressure differences. But I would need to read more to provide a better answer.

[@MadScientist267]

@@jkzero I'd need to do the same but I'm thinking that the idea of pressure differences in an operating tube would have to be caused by these collisions... places where the gas is being displaced by the forces the electrons put on it... distance from the cathode dependent on the potential required in that zone to reach that first bump...

[@victorscarpes]

Yeah, reminds me of tunnel diodes

[@mktwatcher]

Excellent Summary of the Franck-Hertz Experiment and how it confirmed Bohr's Theory of the Atom and specific energy level shells.

[@mikemcguire1160]

I remember doing this experiment as an undergraduate. The tricky part was getting the temperature of the tube right. We messed with if for a couple of hours and then suddenly it came right and with a few minutes we got beautiful result of four or five peaks 4.9 volts apart--very gratifying.

[@jkzero]

Thanks for sharing, yeah, I remember vividly this experiment in particular from my undergrad days, it really changed my way of seen the theory and valued these clever but, but today's standards, quite simple experiments.

[@mellertid]

What happens when the temperature is too low or too high?

[@mikemcguire1160]

@@mellertid The density of the mercury vapor varies with temperature

[@lastchance8142]

Thank you for producing such a comprehensive and clear description of this experiment...especially including the relevant equations!

[@jkzero]

Thanks, I am glad you liked it. The niche of this channel is a mix of historical context, some calculations, and use of original sources (original papers) and the viewers have actively asked me to include calculations instead of just superficial stories.

[@TheMusicPerson]

Wonderful as always. Your videos are some of my favorite on KZbin. Thank you for doing what you do!

[@jkzero]

thanks for your kind words, I really enjoy making these videos so it is great to see that they are appreciated

[@coolcat23]

Indeed a beautiful experiment. I'm touched by the humility shown by Franck at the end of the clip. Einstein had a similar soft-spoken attitude. Nowadays, the en vogue personality is loud, bold, and hyper confident. I miss these classic personalities.

[@jkzero]

Thanks for watching until the end, having that record of Franck describing his own historic experiment is just fantastic. That added to his humble and shy personality adds extra value.

[@darkmedici]

I agree, this is an exceptional demonstration and explanation of this experiment.

[@4kevbot3]

I really enjoy your channel. I’m an out of practice engineer (ie. lost my knack for physics after working in Project Controls/Admin). Keep the videos coming! Bravo!

[@jkzero]

thanks for watching, great having you here

[@nataliadanilov5500]

And when working with people, you yourself become like an electron that flies where the electric field deflects it. 🐹↪↩⤵🐱😄

[@pedrowojciechowski8669]

Interviewer: How good are you in what you do? Hertz: Yes

[@mylittleelectron6606]

I really love the work you're doing. It is the apotheosis of popular science content online.

[@jkzero]

thanks, I am so delighted that viewers enjoy the content as much as I enjoy making it

[@jimsvideos7201]

Thank you for an elegant explanation for such an elegant discovery.

[@jkzero]

a lovely experiment, I really like how these table-top experiments really transformed our way of thinking

[@neirodejesuschancihernande7340]

spent ten whole minutes looking for your channel bro, you definitively deserve way more subscribers, don't halt pls

[@jkzero]

I appreciate that, thanks for the sub, and welcome to the channel!

[@abdou.b3259]

Please make a video for us about the books that helped you in the field of physics and mathematics for beginners

[@jkzero]

I have on my to-do list a video on book recommendations, I will make sure to have it before the holiday season

[@msontrent9936]

Extremely good video. You have a gift of making things simple to digest. I understood everything at first watch. Thanks for sharing.

[@jkzero]

Thanks for your kind comment. I am glad the content can be followed. I really enjoy explaining these things and I miss teaching at universities so this channel gave the opportunity to share all these stories.

[@robertharper3057]

fantastic as always. brought back the same memories of performing it in undergraduate school and then teaching it in graduate school, i sent you some coffee :)

[@jkzero]

Thanks so much for your generous support. This is an experiment that really got me talking about it for weeks when I did it during my undergrad.

[@valentinului]

Amazing content ❤, just watched all your videos about quantum mechanics xD

[@jkzero]

Awesome, thank you! Several people have recently discovered the channel and written saying that they binge-watch the quantum mechanics playlist as well as the playlist on the physics of nuclear weapons. I really appreciate the positive feedback. More coming soon.

[@mrhassell]

The most well video ever made on Frank-Hertz’s work. Excellent!

[@jkzero]

thank you, I am glad you liked it

[@Paul-ty1bv]

I watched the other video. They busted out a slide rule. I loved it. Thanks for the recommendation.

[@jkzero]

I am glad you watched that, I also found the use of the slide rule fascinating

[@AbideByReason]

Another great video Dr. Diaz! I love the logical breakdown of all the physics and math along with the experimental setup, it was really nice to follow. Super helpful including the film from the Physical Science Committee too.

[@jkzero]

Glad you enjoyed it! Those old physics films are a gem.

[@johncope4977]

Another way of looking at it is the mercury electron shell is a resonant body, think of a tuning fork. When the incident electron is of adequate energy it is possible for the energy to transfer into the shell. The shell, vibrating at resonance will then emit a photon whose wavelength will be of the first spectral line.

[@nachiketrao5285]

Your ability to condense complex theories in physics into such informative videos is nothing short of amazing!!🤯 This has been my favourite channel since I discovered the nuclear related videos❤

[@jkzero]

Thanks, I am glad you like the video and I appreciate the good vibes. I just have a great time making these videos and I am thrilled to have found an audience who are interested in the stories and don't shy away from some math.

[@sphakamisozondi]

Splendid upload as usual Dr. By this time next year. Your channel will be bigger.

[@jkzero]

thanks, great to have loyal viewers returning here

[@pAO29Ex]

Thank you, sir. I finally can understand what the corresponding section in my quantum mechanics textbook about the Franck-Hertz experiment is actually trying to explain.

[@jkzero]

I am glad it was helpful, what quantum-mechanics textbook are you following?

[@JamesKaramath]

Just discovered your channel through this - wow! I'll be using this as challenge material for my students going forward, thanks so much, will check out your others too

[@jkzero]

Thanks for your kind comment. One of the most satisfying outcomes of creating content for this channel has been the great number of people telling me "I am showing your videos to my students." I hope you enjoy the rest of the series and welcome to the channel!

[@xSWxSnuggles]

This was my favorite experiment to do in undergrad. I remember if you increase the temp and voltage enough in the mercury triode you could see blue glowing regions like with neon. Cool to learn the historical context around these classic experiments. Great videos.

[@jkzero]

Same for me, I recall the moment when I saw the dips and gave me the shills

[@smartperson1]

What a delightful explanation thank you. That was a fun experiment. And your explanation of it is straightforward enough for me to share with my nephew in high school, while also demonstrating the mathematics.

[@jkzero]

Thanks fro your positive feedback and for sharing. This part of the early times of quantum physics are remarkably simple in terms of mathematical complexity. The whole Bohr model can be derived with just high-school physics.

[@tmo314]

This stuff is phenomenal. Particle science is so fascinating and your videos really make me want to learn even more!

[@jkzero]

Awesome, thank you!

[@Sep-n7w]

One of my favorite experiments explained in detail on the best KZbin channel. 🎉

[@jkzero]

Wow, thank you!

[@DocM221]

Love the videos, keep it coming!!!

[@leon1111er3]

Nice coincidence. I Was studyikg the Franck Hertz Experiment today

[@jkzero]

spooky action at a distance?

[@leon1111er3]

I assume ;)

[@mellertid]

Avoid the environment until the exam, you don't want to lose coherence.

[@stephenhicks826]

When I was 17 in my final year of high school in Melbourne, Australia I studied Physics based on the USA's PSSC course. These films were brilliant. We were also able to do the Franck - Hertz experiment in our school lab for ourselves. I went on to study Physics at University and then onto an almost 40 year career as a Physics teacher. The straightforward presentation of PSSC and historical narrative of modern Physics hooked me on Physics. This video captures something of the simplicity of that old PSSC course. The origin of the PSSC course was almost a direct result of the USSR launching Sputnik.

[@jkzero]

Thanks for sharing; I didn't know the origin of the PSSC courses. Those recordings are fantastic.

[@CDXLIV444]

This is mind blowing. Wish I understood the equations better though.

[@anteconfig5391]

When I saw that old footage of the experiment my heart fluttered and my jaw dropped because I recognized that this was a desktop experiment showing proof of quantization being a reality, and it was so easy to understand. Sure, I read the title of the video and that's why I clicked the link but I was so captivated by this entire video that I forgot why I was here. I love physics.

[@jkzero]

I get your point, I really got goosebumps when I did this experiment with my own hands, memorable moment.

[@jbflores01]

Excellent video! Great work! Thanks!

[@mariacordero6194]

Outstanding content as usual ❤❤❤ Keep them coming ❤❤❤

[@faisalsheikh7846]

Best physics channel❤

[@ProfessorBeautiful]

Terrific! Totally clear explanation. Brilliant conclusion too. Delightful

[@jkzero]

I am glad you liked it. The clip with James Franck is just great.

[@spencerwenzel7381]

Excellent video! This channel is one of the few rare channels that I asked to be notified when a new video comes out. Honest question here, why does only 4.9 eV get absorbed? How about the higher energy levels of mercury like 6.7 eV and 8.8 eV? Why is there only one spectral line emmitted?

[@jkzero]

Thanks, I appreciate that you value the content. You have a great question there; it is tempting to think that at a voltage higher than 4.9 V the electron will reach the next excitation energy; however, since the energy is gradually increased, when the colliding electrons reach 4.9 eV they give their energy off to the Hg atoms, now they are reset to 0 eV, so they start over from zero to 4.9 eV and again they collide inelastically. In other words, the electrons never get more than 4.9 eV of energy because as soon as they reach this value the give it away. I hope that helps.

[@spencerwenzel7381]

@@jkzero Thankyou! That makes perfect sense.

[@janosvarga9997]

That is the way how the striations form I presume. Seems electron needs certain distance to accelerate again to the energy level what the gas atom is willing to absorb.

[@AlphaPhoenixChannel]

Is the image with three half-fuzzy disks of light in neon representing the first, second, and third collisions of electrons with the gas? If I'm understanding that correctly, that's such a ludicrously awesome picture. wow!

[@jkzero]

You are right, those fuzzy discs are the radiation coming from neon de-excitation after the electrons collided with them. I find this image insanely fascinating.

[@AlphaPhoenixChannel]

@@jkzero AWESOMEE! sorry I should have specified first three “energy transmitting” collisions 😁

[@jkzero]

@@AlphaPhoenixChannel no worries, it was clear. Thanks for watching and your comment. I am flattered to have you here, I am a big fan of your channel. You have showed me how little I understand about how electricity works and, weirdly, I love that feeling. Your latest video recording dragonflies was also great, I look forward to what else you do with your new ̶t̶o̶y̶ tool.

[@AlphaPhoenixChannel]

@@jkzero thanks! I think this is the first videos of yours I’ve seen but it’s awesome - I’ll be checking out the rest! I love the science history stuff - I recently discovered another channel called chemistorian I think that does similar breakdowns of old experiments. The historical bits on cosmos were always my favorite too. They learned so much with so little back in the day

[@jkzero]

@@AlphaPhoenixChannel I really appreciate the compliment, specially coming from someone whose work I admire, thanks a lot. I will check the channel that you mention. I love this period in which so much was unveiled with beautifully simple experiments. Most people focus on the theorists, as a theoretical physicist myself I value experimentalist much more as they really managed to find clever ways to probe Nature so I like to share the stories of less-known physicists and the great impact they had on the work of the famous ones.

[@pedronobre3898]

Amazing video quality, as always. Soon, you may become unparalleled in the physics content community.

[@jkzero]

Thanks, I am glad you like the video and I appreciate the good vibes. I just have a great time making these videos and I am thrilled to have found an audience who are interested in the stories and don't shy away from some math.

[@Schraiber]

I think I'm still confused by whats wrong with the naive calculation that results in elastic scattering. It seems like the key there was just that the mercury atoms are way heavier than electrons, not necessarily any assumption about continuous or discrete energy levels. Is the solutuon that the inelastic scattering arises not from bumping into the "atom" in bulk but specifically from colliding with one of the electrons around the atom, which is small enough that there's the opportunity for inelastic scattering?

[@lepidoptera9337]

We had a century's worth of spectroscopic data that showed quantized energy levels. People simply didn't know what to make of it.

[@mernokimuvek]

As a nerd with a hobby of electronics, I absolutely love fluorescent lamps. I even collect old discarded ones. Even if the cathodes are broken, if the seals are intact they will light up without wire near a Tesla coil.

[@jerryking2418]

Very Interesting and crystal clear.

[@angel_machariel]

This was mesmerizingly interesting to me. Going to watch it again because I'm sure I missed a little thing here or there.

[@jkzero]

Thanks, I am glad you liked it, take your time, there is a lot of content in that video, and this is a groundbreaking experiment just like the one in the next video

[@kelleysimonds5945]

Truly excellent explanation and presentation.

[@jkzero]

Glad you liked it

[@Muonium1]

Being mostly self- taught, and in a sort of haphazard scattershot way about these sorts of things, this particular experiment somehow escaped my notice until relatively recently, just a couple years ago. What's so beautiful about it, aside of course from its parsimony in validating the Bohr model, is also the fact that it neatly and completely explains the spontaneous appearance of the regularly spaced bright glowing striations in the so called "positive column" of a DC glow discharge plasma, and how they seem to multiply while filling the same space, as voltage to the discharge tube is increased. Higher kinetic energy of the electrons, greater ability to undergo more inelastic collisions with the atoms of gas along the length of the tube. Simple.

[@threeMetreJim]

That's fascinating. When using Neon, why do the areas of inelastic collision form distinct bands though?

[@GRosa]

My guess is that, when the accelerating voltage is high enough to permit various inelastic collisions, the electrons after the first inelastic collision have time to accelerate to the next collision, covering a certain distance. This repeats after each inelastic collision. In the meantime, the Ne atoms are excited and falling back to their ground state during those collisions, emitting light in the process, which becomes visible as those stacked bands of light.

[@threeMetreJim]

@@GRosa Yes, the collisions cause the light, but why the bands?. The banding would suggest some probability of positions, but why no glowing anywhere else? Do the electrons only 'bounce' in a forward direction? The electron speed only decreases by the energy loss in the collision, they don't need to regain any speed (from what I understand in the video). Maybe the banding gaps are something to do with 'mean free path' in the mercury vapour? I'm guessing the number of bands also is an indicator of applied voltage (number of possible inelastic collisions before the energy is too low to produce an inelastic collision that produces light). Ok I get some of it now, any electrons bouncing backward will have to be accelerated in the forward direction again, I guess this effect causes no light emission in the backward direction as they only reach the energy required to reach the 'collector' at the far end pretty rapidly; they already passed the main accelerating grid.

[@zulumike993]

@@GRosa IOW - the glowing bands indicate the location where the electrons - under the influence of an accelerating electric field - have reached the speed (kinetic energy level) necessary to have an inelastic collision with the Ne atom, transferring their energy to the latter. I'd imagine these bands would compress - and more bands appear at the far end - as the accelerating voltage goes higher through successive increments the band gap energy of the gas atom.

[@GRosa]

Yes, I agree with that except the last part. I don't think it has anything to do with "band gap energy"

[@whataboutthis10]

The emitted light shouldn't have any preferred direction, as it is due to spontaneous emission and 'initial incident electron direction' or anything like that plays no role. The glow of Ne can be observed from any position. Also, the glow is observed after the acceleration is done, through the stopping potential. There is no 'acceleration between the elastic collisions'. Not sure about the glowing 'band' positions tho, the mean 'free' path or more like 'mean _elastic_ path' seems plausible

[@schmitzbeats6102]

I remember learning about this experiment in school. As a class demonstration. We did this alongside other key experiments, some we recreated, like the double slit, and others we studied only as text, such as milikan. On our way to understanding the atom.

[@jkzero]

Thanks for sharing, I also remember the great time I had reproducing many of these groundbreaking experiments. I suppose you refer to the first Millikan experiment, I made a full video about it kzbin.info/www/bejne/eF7YiJR7q72kmKM. His second great experiment is also very important: kzbin.info/www/bejne/nILdmqWhp72Crs0

[@schmitzbeats6102]

@@jkzero Yes the one with the oil drop. I think its difficult to do as a school demonstration.

[@herbanox]

I get to do this today as an undergrad!! Thank you for helping me understand the experiment!

[@jkzero]

Enjoy, it is a beautiful experiment.

[@bili4591]

Oh my.. this is the channel that I search every time in my mind like a fantasy, a KZbin channel that explain rigorously the history of physics discovery

[@barry7608]

Brilliant I’m not overly bright but could follow that, not the formula’s, but the process and its implications, very well explained thanks

[@jkzero]

Glad it was helpful! Don't put yourself down, this is definitely not trivial stuff and a little secret: the math is the easy part, the concepts are really the hard component of quantum physics so you might be more advanced than you give yourself credit for.

[@barry7608]

Thank you very kind

[@davidhand9721]

That neon tube demonstration is just beautiful

[@jkzero]

I find this image insanely fascinating

[@jmmahony]

I think there's a small error in the bottom line at 4:50. The cos inside the square root should be sine squared.

[@jkzero]

Oh rats, you are so right. I checked my notes and I clearly have a sin²θ instead of cosθ. I added an erratum in the video description reporting the typo and acknowledging you for spotting it. Thank you for reporting this, I do my best to avoid these typos but after watching everything many times some minor details slip through. Thanks again.

[@Necrozene]

I guess Stein was busy that day, and Hertz got his day in the sun.

[@jkzero]

I have to be honest, only after the recording of the story I realized that many times I said Franck-and-Hertz way too fast

[@raycar1165]

Is this a The Far Side reference?!

[@Necrozene]

@@raycar1165 It may well be! Thank you for amplifying the joy. Wonderful! Great things surround greater things.

[@jkzero]

@@raycar1165 no idea what The Far Side is, I would have to google it

[@raycar1165]

@@jkzero The Far Side is an art/comic series by Gary Larson. Known for his very simple, one image storytelling. “I guess Stein was busy that day, and Hertz got his day in the sun” Sounded like it could have been one of the captions.

[@randall.chamberlain]

Fantastic presentation

[@ck3908]

Wow, this is beautifully done and so easy to understand. Thanks!

[@jkzero]

Glad it was helpful!

[@DavidMFChapman]

Watched it again. Impressive that they undertook that investigation without any expectation of seeing quantum effects. I always thought if Hertz as a classical physicist but once again we see the overlap of classical and modern back in that day

[@jkzero]

Thanks coming back, many viewers have shared that they watch the videos several times, which I take as a great compliment. The Hertz family involves the remarkable experiment on classical electrodynamics (Heinrich Hertz) and this great quantum physics experiment (Gustav Hertz). Something similar happened with the Thomson father-son, I will get there soon.

[@DavidMFChapman]

@@jkzerooops father and son, I did not catch that. Good reason to watch again!

[@jkzero]

the Thomsons were father and son, the Hertzes were uncle and nephew

[@donk8589]

This is what science should be - exciting and fascinating, not something that crushes your spirit like it's taught in schools.

[@genebrown7920]

What? Your spirit was "crushed" in school science classes? Not mine! I could not wait to get to my next physics class. Every day I learned more fascinating things about physics (and the world)!

[@jkzero]

I am glad you find the content "exciting and fascinating" that is exactly how I feel when I have the opportunity to talk about these topics, this channel is my way to continuously talk about cool physics

[@donk8589]

@@genebrown7920 You were lucky to have good teachers. For me it was nothing but mathematical formulas to regurgitate

[@coolcat23]

@@genebrown7920 Same, I loved physics in school and at university (as a minor subject).

[@giorgiobarchiesi5003]

Great content, explained wonderfully well. Thanks!

[@jkzero]

thanks, I am glad you like the content.

[@fredericharmand]

Very interesting. Thank very much , I didn't know this very astute experiment.

[@jkzero]

thanks, my motivation is precisely to make these groundbreaking experiments that are only known to physicist a bit more mainstream; they are fascinating and not necessarily hard to understand, and their consequences were historical. I am glad that you now know about Franck-Hertz, I hope you think about it every time to encounter a fluorescent lamp

[@АлексейИлларионов-ш5о]

Great video! My lovely how and why physics history telling with results their meanings and consequences. Thank you a lot ❤

[@jkzero]

Glad you enjoyed it!

[@N_0706]

Great video! Could you make a video on the Davison Germer experiment which verified Debroglie's hypothesis?

[@jkzero]

Yes, the Davisson-Germer experiment is definitely coming, I have to cover de Broglie first but yes, this is on the list

[@darrennew8211]

What a very cool experiment and explanation.

[@jkzero]

Thanks, I am glad you liked it. This is indeed a beautiful experiment.

[@fareedjavadi2122]

Very well explained . Thank

[@jkzero]

Glad it was helpful!

[@matthewhoag2609]

Excellent presentation!

[@jkzero]

Thank you kindly!

[@dosesandmimoses]

That is what I saw in my idea of propulsion- brilliant

[@Pepesmall]

Lol he basically said "Yu-Gi-Oh players don't read" before it was even a glimmer in a meme lord's eye

[@tommihommi1]

the deutsches museum in munich has this experiment set up, visitors can move a slider that changes the voltage, and you can see the layers of discharge in the tube

[@jkzero]

I visited the Deutsches Museum a few years back, I was so looking forward to this visit that I went early planning to spend the day there. It was good but I was so disappointed when I was met with a sign reading "all the physics exhibitions are closed for the next year for renovation." FML

[@tommihommi1]

@@jkzero yeah they've been totally renovating everything. Currently only a handful exhibitions are open, but one of them is the atomic physics section.

[@mattwillis3219]

16:48 for one of the coolest physics demonstrations eVaR!!!!!

[@jkzero]

totally agree, this is insanely cool to literally see where the neon atoms "decide" to accept the energy from the colliding electrons in perfect agreement with Bohr's model

[@dleddy14]

Great explanation!!

[@jkzero]

Glad it was helpful!

[@luudest]

Thanks for thins interesting video. I love stories from the dawn of new theories.

[@jkzero]

Glad you enjoyed it! In case you haven't, make sure to check the currently running series on quantum physics kzbin.info/aero/PL_UV-wQj1lvVxch-RPQIUOHX88eeNGzVH

[@pieterduplessis6632]

Great video, thanks for sharing

[@jkzero]

Thanks, I am glad you liked the video. In case you haven't, make sure to check the currently running series on quantum physics kzbin.info/aero/PL_UV-wQj1lvVxch-RPQIUOHX88eeNGzVH

[@MrNescazhou]

Great video, great explanation. I've done this experiment myself. As per my memory, I've observed current drops at other voltages, approximately 11.6V, 13.5V and so on. This is because there is a second excitation potential for mercury of 6.7V and the current drop occurs at the combination of 4.9 and 6.7 potentials. I don't remember if there was a drop/raise of collector current at ionization potential of 10.3V. I wonder, how the authors filtered-out the second potential effect, as shown on the graph at 11:54, probably by the concentration of Mercury atoms or by geometry of the tube. 16:43 - I think there should be a correction to the Rydberg constant here. We can treat mercury as a Hydrogen-like atom and apply Bohr's theory to it. But Rh contains a reduced-mass factor in it, which is different for Mercury because the nucleus of Mercury is 200 times heavier than that of Hydrogen. Am i right?

[@jkzero]

You are right, in general the reduced mass should be used; however, when the nucleus gets several times heavier than the electron then the reduced mass quickly approached the mass of the electron.

[@FoxTails69]

damn... the line about seeing fluorescent lights only old buildings of films MADE ME FEEL OLD hahah

[@no-one_no1406]

Confusing. Why does the peak correspond to the excitation energy step, and not the valley? Assuming the test electrons have a normal distribution in energy, would not the excitation energy point show a reduction in ½ of the target current?

[@pikiwiki]

Excellent explanation. Thank you so much. Is this the structure for Bohr's discrete energy model that he revealed for the atom in the Solvay conference?

[@jkzero]

I am glad you found the story compelling. Bohr's atomic model was published in 1913 so I am not sure which Solvay Conference you are referring to, the first one was in 1911, the most famous one was in 1927.

[@pikiwiki]

@@jkzero in my limited understanding of how controversial the introduction of quantum physics was, I read about how Bohr was "forced" to develop a theory on how individual atoms changed energy states during one of the Solvay conferences, perhaps the one in 1927. The idea, as I was given to understand it, was, there was no smooth increase or decrease as atoms absorbed or released energy. Instead, the energy "jumped" from one state to the other. If I remember correctly, this was a revolutionary way to describe the function of energy change in the orbitals of an atom at the time

[@jkzero]

@@pikiwiki yes, the jump condition was highly criticized from day one and even before Bohr published his first paper in 1913. In my earlier video on Bohr's model (kzbin.info/www/bejne/rnqxg2eDpNaMjMU), I mention that Rutherford was excited with Bohr's model but he was also very critical, his problem was the quantum jumps that appear to violate causality.

[@pikiwiki]

@@jkzero This is the correlation I was curious about. Your exposition has allowed me to understand the mechanics behind "the jump" much more effectively. Thank you for making and sharing this video. I intend to watch your video on Bohr's model to understand more

[@jimgolab536]

This was a really good video.

[@jkzero]

Thanks, I am glad you liked it.

[@luudest]

16:55 How come there is pattern of the radiation? Why does the light not radiate away in all directions?

[@jkzero]

light is indeed radiated in all direction, the pattern arises because the light produced at those particular points

[@lepidoptera9337]

@@jkzero Light from a single source does not and can not radiate in all directions. The lowest possible mode of an electromagnetic field is a dipole. Uniform radiation from a classical light source is the incoherent superposition of many such dipoles.

[@whataboutthis10]

@@lepidoptera9337 'in all directions' is probably meant as a uniform distribution, not that each photon is spherically symmetric around 'parent' atoms position. Just all the emitted photons on average cover all directions equally

[@lepidoptera9337]

@@whataboutthis10 Exactly. So it's not the light that does that. It's the source statistics.

[@GeoffryGifari]

Ahhh I redid this in the modern physics lab course!

[@jkzero]

nice!

[@DavidMFChapman]

Thank you!

[@vinniepeterss]

top of the line video!

[@yeetingkelp8624]

Fascinating

[@tyeadel]

Shows the existence of stationary states for Hg

[@MrRObot-bin]

Grcias Dr. por estos increíbles videos.

[@jkzero]

gracias por la visita y el comentario

[@testboga5991]

Awesome video!

[@jkzero]

Glad you enjoyed it

[@Lolwutdesu9000]

Nice video but the circuit diagram used around halfway through the video to showcase the experiment is slightly incorrect (it's the oversimplified version often shown on the Internet but is flawed).

[@jkzero]

I always welcome corrections, thanks

[@SimulatedEarthboundMisfit]

I ♥ the scientific method. And, "there's no data like real data".

[@jkzero]

plus this can be reproduced even by undergraduate students, it is a beautiful experiment.

[@Jajoo13]

This is so amazing considering the time it was done... Incredibly clever minds!

[@jkzero]

fully agree, I personally love these experiments that require a back-of-the-envelope calculation to unravel such a deep secret of Nature. Another crucial experiment coming soon.

[@Random_Guy314]

Preety damn good video man

[@jkzero]

Thanks, I am glad you liked the video. In case you haven't, make sure to check the rest of the running series on quantum physics kzbin.info/aero/PL_UV-wQj1lvVxch-RPQIUOHX88eeNGzVH

[@Random_Guy314]

@@jkzero sure man I will check it out , you earned a sub

[@supreetsahu1964]

Another goated vid

[@carlbrenninkmeijer8925]

Thank you so much !!

[@Moletrouser]

Rutherford inferred the structure of atoms from the scattering of alpha particles, originally from metal surfaces. The Geiger and Marsden experiment was designed to confirm (or refute) his prediction, which had already been published before that experiment was run.

[@jkzero]

I was not aware of the early publication that you mention, could you share the reference? I would love to check it out