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).
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.
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 😊).
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.
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.
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.
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!
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
@@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.
@@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...
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! 🎉🎉🎉❤❤❤
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.
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.
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.
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.
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.
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.
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.
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!
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.
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.
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.
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!
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 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.
@@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
@@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.
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 :)
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
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!
@@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.
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.
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.
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.
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.
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.
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❤
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.
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.
@@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.
@@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.
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
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.
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?
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.
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.
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.
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.
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?
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.
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
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.
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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-B-uWaEvXqbA.html. His second great experiment is also very important: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fQzirkrXOxk.html
Oh my.. this is the channel that I search every time in my mind like a fantasy, a RU-vid channel that explain rigorously the history of physics discovery
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.
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.
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
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
@@jkzero yeah they've been totally renovating everything. Currently only a handful exhibitions are open, but one of them is the atomic physics section.
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
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.
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
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.
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?
Thanks, I am glad you liked the video. In case you haven't, make sure to check the currently running series on quantum physics ru-vid.com/group/PL_UV-wQj1lvVxch-RPQIUOHX88eeNGzVH
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)!
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
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
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?
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.
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).
Glad you enjoyed it! In case you haven't, make sure to check the currently running series on quantum physics ru-vid.com/group/PL_UV-wQj1lvVxch-RPQIUOHX88eeNGzVH
This what happens when I think about electrical circuits in my car: I want to know how it is happening. I am still learning how to read circuit diagrams.
It doesn’t explain ‘why’ this occurs, only that it does occur. The “why” has to do with wave mechanics between the longitudinal resonant frequency of the nucleus of the mercury atom, which creates the spectral lines or orbitals of the atom; and which also then drives the transverse oscillations of the electron orbitals. If you have ever seen or played with cymatics, where a longitudinal wave (sound) is focused on some kind of medium like sand, you will see patterns emerge, which are unique to the specific resonant frequency of the soundwave. All atomic nucleus are essentially oscillating longitudinal voltage potentials/standing waves in the Aether/ZPE field. And as such, the resonant frequency of the nucleus dictates and manifests where the transverse electron orbitals occur due to wave multiplication/cancellation effects. Its that which makes the spectral lines for each atom appear. It’s all just a matter of the longitudinal frequency of the atomic nucleus. So atomic nuclei are just standing longitudinal waves in the Aether/ZPE field at a specific resonant frequency.
@@lepidoptera9337 Have you seen a demo of cymatics? You can see some videos of it here on youtube. It becomes much clearer when you can visualize how longitudinal/scalar wave impulses drive transverse oscillations, which is the true relationship between the nucleus and the electron orbitals of the atom. The nucleus is a scalar impulse oscillation which drives the transverse electromagnetic waves around the atom (electrons), which gives it volume. Both are Aether/ZPE field phenomena.
Can someone explain me, on the graph at 16:14, why the peak of inelasticity (and so emission) is not refered as 5.5eV instead of 4.9. Woudln't it make more sense that the energy transition is where the curve is locally minimal ?
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.
