Cathode Rays Lead to Thomson's Model of the Atom
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- เผยแพร่เมื่อ 31 ม.ค. 2011
- In the mid 1800's scientists successfully passed an electric current through a vacuum in a glass tube. They saw a glow from the tube that seemed to emanate from the negatively charged plate called the cathode. Since scientists didn't know what the glow was they called it a cathode ray. There was debate over whether the cathode ray was a wave phenomenon like light or a stream of negatively charged particles. JJ Thomson effectively resolved the debate in 1897 by performing a clever experiment that determined the charge to mass ratio of the particles making up the cathode ray. He also showed that this same particle was in all different cathode materials so it must be a constituent common to all atoms. This changed our understanding of the atom from the previous billiard ball model to Thomson's plum pudding model of the atom.
"What's an electron?"
"Well, think of it as a plum pudding..."
LMAOOO
Atom as a plum pudding, electron as a plum
Thomson told think of an atom as a plum pudding not the electron.
Watermelon and Christmas pudding, in our book
Lmao
9 yrs passed and this was the 1st video of yours that I saw
"Electromagnetic Fields and Waves" by Lorrain & Corson (2nd Edition) contains a problem in chapter 2 "Electrostatic Fields in a Vacuum" (2-19) on J.J. Thomson's "Plum Pudding" model of the atom. It asks to (A) find the force on an electron; (B) describe its motion; (C) the frequency for a 1 Angstrom-sized atom; and (D) compare this frequency to that of visible light.
A rather thought-provoking question in an Undergraduate E&M textbook!
1:50 Derek listening like a serious student
What we see here raises more questions than it answers. I was looking for a ray and I see rising doughnuts of purple light. Also, do the electrons that were pulled off the cathode return? If so, how and when do they return? If not, where do they go?
There's an anode at the other end - that's where they go to. They speed up slowly until they have enough kinetic energy to knock an air molecule (mostly nitrogen) up to a higher energy level. These molecules then drop back to the ground state and emit light. In the mean time the electron's lost all its energy and has to start accelerating again. Hence the breaks in the illumination
eventually the electrons get to the anode, and head around the circuit to do it all again... unless they hook up with another nitrogen or oxygen positive ion and live happily ever after
@@PhilUpOnScience I have a question if the electron have to start accelerate again then why it gives the break in illumination. why all the electrons do not hit the first nitrogen molecule near cathoide? you get what I mean?
@@winproduction7585 They lose their energy in the first collision (which lights up the gas). They don't cause any more illumination until they have again amassed enough energy to knock a molecule up to its first excited state.
I thought this was a vacuum tube. So there shouldn't be any nitrogen or any other air molecule in there, right?
I am loving to watch your old TH-cam videos. And do you know what?
I just thought that it may be possible to start to present those videos to my 8 years old girl. They are shorter and simpler to understand. Perfect for kids!
Thank you very much for making such nice videos over the years.
i wish they would explain how the electron produces the light, like a schematic from the cathode to the anode
Light, or photons, are emitted from atoms when an electron gets closer to the positive nucleus of an atom. Hope that helped
When High Voltage is passed through electron it excites and goes to unstable level. Then it comes back to a stable level and emits photon(light)
They speed up slowly until they have enough kinetic energy to knock an air molecule (mostly nitrogen) up to a higher energy level. These molecules then drop back to the ground state and emit light. In the mean time the electron's lost all its energy and has to start accelerating again. Hence the breaks in the illumination = "striations"
@@PhilUpOnScience the cathode ray is produced in a vacuum - there are no gas particles
@@patriciahugman5285 It has been pumped down, but not completely. Even in outer space, a vacuum way better than what we can achieve on earth, there are still roughly one particle per cubic centimetre. As the vacuum improves, the dark space and the striations get further apart, as there are fewer particles to collide with.
1:58 that looks like a shark.
At first I thought you were talking about the dudes hair Ha!
P.s. Love your videos and don't think u try to make ppl look stupid (and never watched the full interviews)! And love the point about "unknowledgeable" vs. unintelligent.
it reminds me experiment of thermoemission in physics lab. like the force they were talking was a heat emitted because of R of the cathode.
This raises so many questions:
1) If they were expecting to see "nothing or a spark", how come they saw they "saw the same glow no matter what metal they did the experiment"?
2) How on earth did they measure the size of this particle to conclude it is smaller than an atom?
3) When does this particle (electron) become a photon and how does that conversion work?
1) well the first guy expected to see nothing/a spark, once he got this glowy contraption, every other guy wanted to do the same test and subsequently the tests concluded there's this "glow, no matter what metal they used"
2) until then, we thought every element breaks down to its fundamental particle "the atom" which couldn't be broken down to smaller particles. Then they saw this glow and theorized there has to be some tiny _particle_ traveling from the *intact* cathode to the intact anode.. suppose the cathode atoms were travelling through the medium, it'd disintegrate the cathode and accumulate on the anode (like electroplating). An intact cathode meant whatever the particle, was given off by the cathode atoms and travelled through the anode atoms to complete the circuit. And all metals tested had this particle, so a flowing current meant this particle has to be moving through them.
3) it doesn't *become* a photon, one of the loose electron accelerating under the electric field, hits an atom wandering in the vacuum, which imparts it's kinetic energy to a native electron in the atom, such that the native electron of the atom gets excited and jumps to a higher orbit/energy state, (but sans enough energy to rip the native electron out from the atom) which isn't a stable setup/equilibrium) for the atom,
Losing its potential energy to settle back to its orbit, the electron pulses out a photon, which in this case is in the visible spectrum.
Suppose the air had more of another element than nitrogen, say -calcium vapor or xenon, the electrons that get excited to (the outer orbit electron) jump to a higher orbital, would release a calcium specific color(brick red, I guess)/xenon specific color(dim blue grey) and this can be used to analyse what element constitutes the said gas.
Sodium gives bright yellow when its outer electron gets excited..
This also means sodium vapor absords yellow colored radiation best, such that it's electron gets that specific energy to reach that specific orbit..
Same behind JWST analysing the presence of certain gases in distant planets..
All answers are recollection of memory from highschool classes and my guesswork.
I'm neither a physics/chem major nor a native English speaker. Kindly excuse and feel free to correct.
1) the negatively charged particles (electrons as we know now) hit the ZnS screen or any other fluorescent material to produce the glow. they also cause the ionization of gases in their path. since all electrons are same, they cause the same glow which led to the conclusion that these negatively charged particles are fundamental quantities of every atom. :)
I'm still a student, so I am not very sure about the answers to 2) and 3). Hope this helps. Please correct me if I'm wrong. :)
@@dipteeshukla7 i think you're referring to the gold foil experiment, where a beam of alpha-particles scattered by a thin gold foil, was picked up with the Zn sulphur screen.
I'm not sure electrons can be picked up on ZnS screen, also, the glow in this video is seen in vacuum and not on any screen detector.
@@andrewthomas310 but we'll require something to observe them as cathode rays are invisble...
How he says ‘laindmaak’ 00:16 (land mark) is the most Australian thing ever
1:50 distracted by the vac pump. It looks like a shark! Lol
Pretty old comment
@@ashutronomy3448 old indeed
Actually the brand was Shark 🙂@@maruftim
@@PhilUpOnScience umm okay?
Watching this 10 years after it was originally posted!
🤝
This was helpful I wish I can study in your university
This guy might become a great channel a decade later
Sarcasm😏😏
@@IIT__2024are you in any iit?
@@abhinavmartandjha0369 nope
any one else watching this because they have too
Go play fortnite
why wouldnt you want to watch this? embrace school. you have no idea how much you will miss it
This title is anti-clickbate
And to tie this to the pudding synonym, there might be a dwarf around putting more plums in as you take them out.
Why can't you see a continuous "spark"? is not an effect of the camera, I've done that experiment with a flybak, a bottle of wine and a fridge pump and you can see the spark discontinuously. Is it because the high voltage is not continuous but pulsating?
What happens after you turn the power off though? ... I mean during the experiment all the electrons are "sucked out" of the cathode if I understood that right? What remains? Will the cathode be forever positively charged after we cut the power? Or how do the electrons get back to the cathode?
Where do the electrons go during the experiment? Will they just stick to the anode and remain there as long as there is power?
for every electron that comes off the cathode, one goes into the anode, so it balances up. This is because the anode and cathode are connected through the power supply. (There are ways you can charge up a cathode and leave it charged though - eventually the electrons get bumped by passing air molecules, taken away, knocked off etc and so the charge dissipates)
your video is a life saver thanks very much. kinda got a write a paper on this tonight :/
what happened to the paper ? :D
@@sparklypri lol
hope you did well
Experiment first conducted in 1857 ...wow some really intelligent people that time.
Analogies are great but care should be expressed when they help "imagine" what's going on vs. replicate the mechanism of action. Which makes food analogies great as they are self-evident for imagination purposes only!
GUYS, LOOK OUT!
THERE'S A SHARK ON THE TABLE!
Seeing young Veritasium is something veryy delightable
@sushicartman01 My guess is the frame rate of the camera. Kinda like how if you watch a video of a car driving down the road, the wheels can appear stationary.
thanks, helped a lot! :)
He has changed so much but i really want to talk to him..... love his vedios
Wow! This is such a great youtube channel!!!! I am a student and if only my teachers made chemistry this interesting!!
Ever wonder why they don’t just show us an electron or atom but always want to explain it
@@jayizzett 😂😂 yup.
@@shivaranjanigr4750 it’s all theory … :-/
@@jayizzett what election 😂
@@shivaranjanigr4750 electron. Thank you
Australia. If you like the waves you're bound to encounter a shark eventually.
Is the setup you made basically the same as an X-ray tube? if so, weren't you exposed to x-rays when you started the machine?
Yeah, probably there were a few. Not sure if our voltage was high enough, but the current was low enough to make sure if there were any it was not a large number of them
What is the speed of electrons in cathode rays?
cool experiment
Why is there no glow when the pressure is higher in the discharge tube?
and why does the glow again disappear after lowering the pressure below a certain value? It would be great if someone explain it to me , please.
When there is air inside the tube, the molecules of the air would absorb the energy released by electrons. And so there will be no glow. When there is no air, there is no one to absorb the energy and so the electrons can be seen releasing the excess energy(cathode rays).
science hour But cathode rays are what we call the electrons . They are the one and the same thing .
What makes the glow is the electrons from the gas molecules being excited by the energy of the electron ray (cathode ray). What you see isn't the cathode ray itself, but it's effect on a few gas molecules. If you take away the gas, the cathode ray wil still be there, but you won't be able to see it.
+Daniel Spesani If this is the case then why can't we observe the glow even at a higher pressure (more gas molecules) ? The same occurs when the pressure is considerably low .
Because if the concentration of molecules is big, the energy will be divided among many atoms, thus the energy in each individual atom won't be enough to excite the electrons. Try to imagine that you want to boil some water, but your power source can only give 500 watts. If you put it in a cup of water, it will boil without problem, but if you put it in a lake, the energy won't be enough to boil that much water.
Loved that ending perfect preparation of nuclear chemistry.
What gave Geissler the idea for this particular experiment in the first place? What was his hypothesis
I’m gonna apply a high voltage to my plum pudding to see if any plums come out
Is that a stationary wave? Does that explain the 'sections' you can see?
No that's probably just an effect given by the camera only being a certain amount of frames per second. If you looked at it live you would see a continuous line
is this how a neon lamp works?
Thomson was relentless in his pursuit
The wave and the particle....a vortex of electromagnetic potential and the substrate of "physical reality", where energy manifests into matter.
electricity in quantum theory is the electromagnetic wave that travels between electrons , creating current, that's why the speed of current in a cable is close to the speed of light, while the drift velocity of electrons is much slower , and analogous view is that this electromagnetic wave is just photons being transferred between electrons.
particles are waves, and waves are particles.
When I said electrons were waves, I was referring to the double-slit experiment and quantum mechanics.
"One thought it was waves, and another thought it was particles." Funny how both turned out to be right :P
i think it wil finaly run out of negatively charged particles but there are so many of them that it takes a huge amount of time. not sure though
how much is the vacuum in glass tube?
I was distracted by the Orb stuck to the outside of the tube
once it was turned on, what is that, is it the Moon.
Good job 👏👏👏
Why does the "solid-appearing" ray look like it changes into a bunch of slow-moving purple blobs?
did you find out?
@@daifukuu Read a different comment about camera frame rate making it look like discrete blobs but your eyes would perceive it as continuous. Haven't confirmed but it sounds reasonable
inset this how xrays are made? x rays use a filament and a high voltage discharge in a vacuum.. very similar to this
How the uniform dark spaces produced can you explain
Is the electron discharge a form of radiation (of electrons)?
Not really, because they are matter... unless you take the radioactive radiation definition, in which case beta radiation is electrons, so it kind of fits that categorisation... except it doesn't come from a radioactive element... a bit confusing - it's semantics really...
But what is causing the light? Collision with gas particles?
this also marked the beginning of x-rays right? lol I don't know. but man, crts were a quantum leap
DANGER! DANGER! 0:28
So electron can travel without ionising?
Loved it , just loved it ,😍
@MrStemkilla yeah this reminds me also of my radiology class :D
@fcoalvaradov what are the direct effects of exposure to high amounts of radiation? we all know radiation poisoning but do you know of what is going on on the cellular level? yes all i know is from simplified diagrams and little bits i have picked up. what you stated was fairly interesting
Plum pudding but plum as -ve and remaining +ve so great
Very good! Now can I have some pudding?
good video
so the tube is fully empty (vacuum),which medium carry's the electron to anode
There's no need for a medium to carry electrons, they just leave the atoms of the cathode (metal at the bottom) and travel to the atoms of the anode (metal at the top).
You need a bit of medium inside if you want to see the rays. Electron beams are invisible to human eye. They appear to be visible because they excite the gas atoms in their path which in turn emit photons/light when they de-excite/capture an electron.
Yashas Samaga
You're absolutely right. However, the OP asked which medium "carried" the electrons, and there's no need for a medium to "carry" them. I was answering that question.
Well, the electrons are coming from your power supply, if they stop generating them they will stop flowing. There will always be electrons in the metal, but they are bound to the protons.
From your question it sounds like you thought that the particle was something other than an electron. But that was the point of this experiment, to prove the existence of the electron.
The most recent comment on this was from 2 years ago
This was on my home page, soo why not watch it.
* one year ago actually...
No 5 months
At that voltage that's a good way to expose yourself to quite a bit of X-rays!
bro is that Glenn McGrath
Consistency pays...
Good eye balls!
Still didn't show how charged 'particles' exist except from a quote by JJ Thompson..... Show us proof that electrons exist
You can’t exactly “see” those particles if they’re moving nearly at the speed of light.
@fcoalvaradov well what do you know about this type of things? i have never taken the class myself i just know that how they are made or have been made
@MrStemkilla well radiation hits the cells of the body and the body absorbs the energy, the more dense is the tissue it hits the more it absorbs... there are specific tissues very sensitive to radiation (the cells that duplicate more) and basically this damages the cell membrane, cytoplasm, and the nucleus. This leading to damaging the DNA and further cellular problems. :)
the acute absorption of radiation can lead to acute radiation syndrome which is nausea, vomiting, intestinal bleeding ...
You didn't put a magnet up to it to prove the negative charge of the electrons!
how is it that the cathode doesn't run out of this negatively charged particles? After all, you can only pull so many plums out of a pudding :P - Just Jon
Because a constant voltage is supplied...
no condescending wonka= no learning
can u make a video on .."Which way does Electricity REALLY flow?"
Electricity flows bcoz of negatively charged electrons? but when we connect a bulb to a battery ...both +ve and -ve charge-flow goes in two opposite directions at the same time. and what happens when a human body get electrocuted??
+Ashish Parihar When electricity was discovered, they had to decide on a notation, so they decided on + for the anode and - for the cathode. Later on we discovered that electrons were the reason that electricity, flowed, and it was flowing differently than we expected. Electricians still use the "conventional" (i.e. incorrect) notation of + for anode and - for cathode, even though it's not really accurate. When you connect a bulb to a battery, it flows from - to +. This is DC (direct current). When you connect a bulb to the wall, the + and - are switching constantly (60 times a second in the US and 50 times a second elsewhere). This is called AC (alternating current). Your body has a capacitance, which means if you put electricity through it, it will charge up and electricity will start to be blocked. This is why batteries, even really big batteries, don't hurt you when you touch them. Since the AC power from the wall is constantly going back and forth, it charges and discharges capacitors (like your body) very fast, and it can have a greater effect. Ultimately, it's the electricity that tenses up the wrong muscles (like your heart) that causes problems.
Hope this answers some of your questions.
@@DaffyDaffyDaffy33322 well explained
@@DaffyDaffyDaffy33322 very well explained
Jazakallah
@MrStemkilla haha and I know what are the effects on the humans, as diagnostic tools and I have investigated a bit about radiation effects. I know just the basics on how they are made for diagnostic purposes. X rays, the more interesting are SPECT/CT, and PET/CT tomography scans.
spect stands for single positron emission computerized tomography, and pet for Positron Emission Tomography... YES! positrons through our body and inside it!!! ;)
@fcoalvaradov i didn't know it damaged the other originals of cell :) but i knew the DNA part :D do you know of any tests done with exposure to very high amounts of radiation and the effects of that? like what they use to sterilize packed things? i think about 200 Rads a second Gamma.. yeah well what would happen apron exposure to that because that is high enough to kill cells on contact and its effect on a multi-cellular being would be interesting.
another greek word: anode -> άνοδος (ανω + οδος ~(up + road))
Les électrons sont les raisins secs de l'atome!
I dont know if there is an electron i only see a a purple colour 🙄 how identify?
7173D
Good
well particles can behave like waves so your argument is invalid i'm afraid. It's called the wave-particle duality. And not just some particles because then it would be called the some-paricle-wave duality. No, every particle can ( note the can ) behave like a wave and every wave can behave like a particle. Tho it is true that some particles are more often behaving like particles ( that's why we call them particles ) example: UV-light (or rays) are waves made up of fotons which are particles.
derek's got a great cowlick in this vid
What's plum pudding 😞
Derek seems bored.
what is the importance of metals here ?
the electrons in the outer shell of metal atoms are released more easily. metals are conductors ie allow the flow of electrons.
Thank you
Great
isn't the anode the negative side?
No, anodes, like anions are positive.
EPaR - Aidan Gieg the anode is positively charged which attracts anions which are negativity charged as unlike charges attract
Anions are positively charged, too. Cations carry a negative charge.
Zuzu Superfly How immature. Just say "anions are positively charged" No need for the insults, you wouldn't do that in real life now would you?
Dean Kruse Nope! Anode is positive (defined as the side that attracts anions).
Regrettably, now the model is actually not perfect. An atom doesn't look like that pudding it once did anymore. The Yum Yum model is just out of date! :(
Professor looks a bit like Glenn McGrath.
I thought Helium atoms are smaller than Hydrogen. Can anyone confirm this because he said that Hydrogen atoms were the smallest.
+Internizer Hydrogen has an atomic weight of 1.00794 while Helium has an atomic weight of 4.002602. Hope that clears it up for you.
+Internizer The problem is that in nature exists H2 (two atoms of hydrogen linked together), and He (a single atom of helium). So natural hydrogen is bigger than helium. A single atom of hydrogen tends to combine with anything, so it's quite impossible to get a simple H, even if theoretically hydrogen should be smaller than helium.
+unpopiuinla Those conditions apply here on Earth. Yet, most of the hydrogen (its not theoretical) in the Universe is in it's atomic form.
the key word here is atom, H is an atom. H2 is a molecule. so an atom of hydrogen is the smallest ATOM.
Ilgor , so in the universe hydrogen avoid the most common laws of chemistry?
Arent cathode rays are invisible light stream ?
+sachi codo beta (electron) particles
+AAA SSS No
They are NOT light but however they are invisible. They appear to be visible in the experiment because the electron knocks out electrons from the gas atoms when they collide and when an enter enters the exicted atom, a light ray is emitted which is why you can see the path of the rays.
"main camps" I read'em a "Mein kampfs". ROTFL.
111,111 in 2015! w00t!
158,005view
937th like
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Wow! what are the odds?! 0-0
Hey I wanna come there.....
that balls