What is the Photoelectric Effect?
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- Опубліковано 9 лип 2016
- The 3rd in the series on the photoelectric effect
(See my videos on Hertz and Planck
- Hertz - • Hertz and Radio Waves ...
- Planck - • Black Bodies and Planc...
Covers how observations of the photoelectric effect lead to Einstein's theory in understanding the effect.
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Very well done. Complete background, and clear.
Excellent. Brilliant. Simple, to the point
You are a true legend! These videos save me every time
These videos are extremely brilliant. All the stuff is explained precisely.
U explained it 1000001% better than my school and tuition teacher
Thankyou.
Frustration 🤣🤣🤣
Can't say a word!!
You interpretation is brilliant :')
Thanks for the video. Really helped in my teaching of the subject as a new inclusion in Physics
Thanks man. Appreciated.
well explained video. Tq
This video saved me!
You are an amazing explainer sir.... Thanks for the high quality lectures.
You’re welcome
Thank you!
You saved my life sir!
Thank you! My HSC exam is tmr, and hopefully I understand it well enough. Idky, but this for me was one the hardest concepts of the entire course.
Good luck for tomorrow. I’ll be releasing the answers later this week. (No, I haven’t seen it yet) 😄
I like ur animations
Hello, whats up? the video is really great! Great explanation. My question is if in the Lenard experiment it had been considered the theory about the electons speed taking in consideration that an electron in a constant electric field supplied by the power supply would accelarte with constant accelaration, but that theory the speed end up to be constant because the electrons hit the crystal structure of the conductor (copper or aluminium). So wouldnt it be matter about the accelaration of the electrons in the gaseous spece since when they hit the conductor applies the theory the an electron speed would always be constant in a solid conductor. Am i right?
Thanks very much important
If you could explain the concept of ladders this way i will be very much great full
Is summary on page 2:56 was drawn from observation and apparatus on page 1:55 ?
If so, is the reading in the current meter represents the speed of electron?
If so, how may we explain current intensity can represent electron velocity?
19:25 dependent on material, AND ALSO MAYBE TEMPERATURE??? Easier to emit electrons if the temperature is higher, because less work to get them free??
I think your animation could be made better if you made it clear that the voltage applied to the plates served to keep the electrons released from reaching the right hand plate. Only electrons with sufficient kinetic energy would overcome the electric field and make it to the right hand plate. Otherwise excellent video.
Hi, I'm a Physics student from Brazil and I find your videos so usefull and motivating for me!! I have a question and thought you might answer it:
The "classical" kinetic energy is related to the velocity, can I relate that to the kinetic energy of the electron? I know the velocity is constant in the quantic world... Are they two different concepts?!
Thank you,
Ana Luiza
Yes, to a degree. the KE is determined by the rest mass of the electron. But an electron has a deBorglie wavelength.
I found this link that may be useful : physics.stackexchange.com/questions/223288/kinetic-energy-of-an-electron-with-de-broglie-wavelength-lambda
I have a question. Why if you continue to increase the temp. in the light bulb filament does it not emit xrays. Is it because electricity does not have the required frequency to make the tungsten filament emit xrays.? Is the frequency of electricity 60 hertz?
I do not understand how the increased energy per electron, which comes with increased frequency, can be measured with the apparatus you show. From Ohm's law any increase in voltage would produce an increase in current (shown in your ammeter) - the same effect produced by an increased intensity of sufficiently -energetic light - unless the internal resistance of some part of the circuit increases in proportion.
While this is relatively alright to overview this, there is a gap in explanation of WHY the ultraviolet catastrophe suggests discretion over continuity. This is like if one were to fill a balloon with some substance, like a gas, where you notice it rises at some rate and guessing that it should continue to rise forever. But when you discover it only goes a certain height you discover it experimentally falls suddenly. You can guess that perhaps the balloon expanded so much it blew up and then suddenly fell because of this. But you don't then infer that the balloon rose in discrete steps. You need to connect the actual thinking that links one logically to share the inference. This is not done here. (or, rather in the leading prior video that was meant to aid in understanding motive for the photoelectric effect better.)
I also have to add that I don't personally even see how these past scientists presumed that increased intensity SHOULD require faster electrons.?? They knew by then that there was a speed limit to everything by that time. Given that alone, you can interpret the above experiment in kind to using a bell that you hit. The 'sound' is both a wave where it also acts as a discrete packet of information when heard. Increased energy of a strike isn't expected to make the sound pitch higher for hitting it harder. The properties of the bell determine its pitch only. And the 'packet' is how the recipient receives and translates the information as a pulse when heard. Increasing the 'rate' of pulse to become constant still wouldn't raise the pitch. [And note that the difference of media allowable for light through a vacuum over the limitations of a sound being restricted through air is irrelevant here. I can expand on this if asked.]
Basically what the photoelectric effect boils down to a childish analogy of marbles hitting marbles, that light and electricity must be made tiny particles (Of zero volume I may add, whats a particle with zero volume ? Answer Nothing !) because how else could they be released from the metal plate, which is a really ludicrous presumption, as we know vibration can shake and break apart matter, so why should it not be true of electrons, thats assuming electrons (discrete packets) exist in the first place.
Quantum physics is nothing more than the Kabbalah (Jewish mysticism) repackaged, they are obsessed with numbers, they assume numbers is the language of God so are determined to push the idea the proven analog universe can be broken down into quanta or COUNTABLE particles, their whole belief system relies upon it, and as they own the banks and much of the media and academic institutions, they have the clout to push this LIE a not particularly well though out lie once you get past the verbosity logical and mathematical fallacies and parlour tricks.
I was thinking exactly this. I am still trying to understand the justification for inferring discretization of light from this
Sir.. I'm a little bit confused.. at 3:55 it's said that intensity is energy.. and later I understood that the energy is connected to the frequency and that's a different notion than intensity. So would you kindly make it clear?
And really.. that is an amazing video. Thank you a ton.
He later explained that intensity isn't a measure of energy, but a number of photons produced by a source per unit time. Energy is determined by the frequency of the photons, however classical physics explained light as a wave, which light is now thought to be a particle with wave-like properties.
Very nice video. Congratulation. If you could be kind enough to answer me i have one question about black body radiation. (I hope my English are correct). How Planck explained with his ypothesis the fact that at the diagramm of a black bodys radiation there is a maximum at a certain wavelength. I understand that with athe previous theory the icrease at the wavelength would lead to decrease to the intensity( per wavelength). I know that with his ypothesis he wrote an equation that was according to the experimental data but i want to understand it with physics and not with mathematics.
Planck didn't do any "new" physics here. That's what experimentalists do. It seems to have been Otto Lummer and Ferdinand Kurlbaum who came up with a reliable source of black body radiation in 1898, after some 40 years of more or less unreliable experimental techniques. Planck just provided the theoretical ingredient to understand the measured spectra. Individual quanta of light wouldn't be measured for another 27 years, or so. I think the usual "discovery" of that is assigned to Compton and the Compton effect. Individual optical photons were first detected with photomultiplier tubes around the mid 1930s.
hi, why voltage doesn't change when he tweaks with the parameters (only current changes)?
Thanks for brilliant video. I have a question, Can I use photoelectric effect to measure incoming infraRed wave? does it have enough energy to liberate electrons from gold plates for example?
Red is pretty low in terms of energy. It will need to be greater than the work function of gold. 600 nm which is red has an energy of about 2 eV. Gold work function is over 5 eV. So it won’t work.
Yes, you can, but not with metals. Semiconductors, however, can be used deep into the infrared (if you are willing to cool your detector below room temperature).
Svarnas was here.
If the electrons are being ejected from the metal surface from the photon energy, how does the metal replenish those electrons, or does it leave a charge, or just keep losing electrons?
The way this works is that the photo voltaic sell complete an electrical circuit so the electrons go to the other side, the anode, and then continue around the circuit back to the photo voltaic cell
Sir can you please tell
What if hf- threshold frequency is 0
That’s not possible. Means electrons aren’t held at all
Please help.
you have a light source with a frequency equal to the critical frequency of a metal sheet, if you make the source nearer than it was, does the current intensity caused by the photoelectric effect increases or still the same?
My teacher says yes it will increase due to the square-inverse law.... but i’m not convinced because this phenomena happens by the particles of the light not the wave and the photons doesn’t consider the inverse-square law.
Am i right or what?
Intensity plays no part
When is the frequency EXACTLY the threshold frequency?
Rarely.
If it’s under, no electrons released
If it’s over then they are , albeit at very low kinetic energy
So you are right.
@@PhysicsHigh thank you mr I appreciate it❤️
But could you simplify it with easier words😅 because I’m Egyptian and i barely know english
Hi Sir I was wondering, how does having a battery help measure the energy of the photoelectrons? can't we just put a voltmeter accord two plates without the battery?
A voltmeter actually needs a current to work and to determine the energy precisely, once a small current is generated the voltmeter would not be precise enough.
By adding a stopping voltage allows it to be measured precisely
@@PhysicsHigh Thank you very much, appreciate it!
@@PhysicsHigh good evening sir, I suddenly just wondered why does the electrons from the metal liberate towards the vacuum, wouldn't it be easier if there is a potential difference that the electrons just flow through the wire at the other direction instead? I guess in this example to the left instead of jumping a vacuum to the right. Sorry I am still new to this subject, one reasoning that I thought of is maybe it follows the directions of the reflected light? but if so why does it do that?
i am sorry but I have one point that i do not understand, as from my understanding, electric current was not dependent on intensity, just like a brilliant source of red light might illuminate the surface without any effect, while a feeble source of ultraviolet light would cause a current. It is right only under the situation that it is UV light?
+Lai Tiffany not sure what your question is?
Sir I didn't get it. Can you explain it in more detail
Gigachad💪💪💪💪
So can we take the blackest thing and make solar panels out of it using this effect?
Not really. A black body will simply release all energy absorbed in the firm of EMR. It’s not material dependent. For the PE effect you need a very specific energy to release photo electrons from the atoms. That is material dependent.
How was the first photo cell made tho
You take a piece of metal and irradiate it with UV. If you do this in vacuum (which is not necessary) we talk about a "photo cell".
what would be wrong to see the observations of this experiment and simply conclude (mu hypothesis for discussion sake only) that electrons can only absorb quantized amount of energy?
We can accelerate electrons in an electric field to an arbitrary energy.
There are no particles. If you pay really close attention to the experiment then you will notice that it is completely macroscopic. We are not observing individual quanta at any time with it. Typically measured photocurrents correspond to photon fluxes (or better "frequencies") of 10^8 to 10^12 photons per second or so (with pulsed lasers we can nowadays make photocurrents of several amps and we are doing that in certain types of accelerators).
What high energy physicists (that's what I like to call myself) are measuring are combinations of energy, momentum, angular momentum and charges (electric charge, leptonic charge etc.). You can easily verify this by reading the technical design documents of e.g. the CERN detectors (ATLAS, CMS). They are freely available to the public. You will quickly notice that high energy physics detectors are not trying to measure "particles". They are measuring energy deposition in the matter of the detectors. The patterns (tracks) of that deposition process allows us to reconstruct the energy, momentum and charge exchange between the free field (the physical vacuum) and the detector hardware.
The physics of how we get from quanta of energy to "particle tracks" was elaborated very early by Mott in a 1929 paper. You can find it online, if you want to read it. It's one of the most important papers in physics history that almost nobody seems to know about. It's the first fully worked out example of "weak measurement" that I know about. Heisenberg talked about weak measurement a couple years earlier, I believe, but he didn't flash it out theoretically. What basically happens is that we are measuring consecutive scattering processes of the original quantum that spawns ever more new quanta of ever smaller energy but with more of less the same momentum. It's the compound probability formula that connects these individual location measurements of these quanta to what seems like an almost straight line. It's basically a random walk process overlaid on a large momentum state.
Particles are a figment of the human imagination. We made the same mistake twice before, when we identified heat energy with a mythical "Stoff" called phlogiston and were looking for a material carrier of energy in the vacuum, which was called "ether". The "particles" in poor explanations of quantum mechanics are just that: imaginary beasts that derive from the same material carrier fallacy. The human mind likes to imagine "stuff", even when only properties are changing. It's not limited to physics, either. In economics many people are misidentifying money (which is just an exchange quantity) with the need for a physical representation, like coins, printed notes, gold bars or even some computer code (like bitcoin). None of that is needed to transfer money and banks aren't working that way. They are simply updating account ledgers with numbers. Money is an abstract exchange of value that is assured by synchronization (balancing) of accounts. That is exactly the same mechanism that nature uses for locally conserved system properties like energy, momentum, angular momentum and charge.
So if you want to teach modern physics correctly, even at this level, try to tell students NOT to imagine things that aren't there... like particles. I admit that this kind of mental discipline probably would have to start in kindergarten and preschool... by the time we get to high school physics it's kind of too late to remove poor mental habits from student's minds.
Doubt : You said that planck’s theory could not explain the black body radiation, but can you explain how could Einstein’s theory explain the photelectric effect
Planck did explain the emission spectrum correctly and Einstein did explain the absorption behavior of light on metals correctly. The important thing to realize is that "quanta" are ALWAY associated with irreversible phenomena like emission and absorption.
How planks discovered the constant. I mean what the experiment he did exactly
He didn’t do an experiment exactly. It was a mathematical analysis based on the assumption that energy has to be quantised.
Unfortunately for generation after generation of kids the high school version of the photoelectric effect suggests that photons and electrons are material particles, which they are simply not for the purposes of quantum mechanics. We could treat electrons as classical particles in non-relativistic electrodynamics, but in that context we have to treat light as a wave phenomenon. The "classical" and false way of teaching then proceeds to modify that picture into photons as corpuscles, which is completely wrong both in the classical and the quantum regime. Light, when quantized properly, is still a wave phenomenon, but it's a wave of a quantum field rather than a wave of a classical field. Incidentally electrons also become a wave phenomenon, which is diametrically opposite of what we are teaching at the high school level.
Our teachers need to think this over because they are not doing kids any favors by actively lying to them about physics.
This does not prove anything about the properties of light. Only that light is emittet and absorbed in quanta. But is it a wave or a particle depending om the measurements og only a wave. There is no reason to think it is anythink than a wave.
You are correct. The photoelectric effect does not prove field quantization. For that you need to look at things like the anomalous magnetic moment of the electron.
Still doesn’t explain the theoretical interpretation as Planck implied
Planck has nothing to do with the PE. This is Einstein.
The animation is, unfortunately, completely wrong. Photons are not particles of light. We should not be teaching this at the high school level. Photons are quanta (small amounts) of energy. To suggest that they behave like particles sets people up for a lifetime of misunderstanding about quantum mechanics.
How do you define particles? I’m not suggesting that they have volume or mass only that they are discrete entities that are indivisible. Particle physicists are happy to call photons as particles as are all components of the standard model.
There are no particles. If you pay really close attention to the experiment then you will notice that it is completely macroscopic. We are not observing individual quanta at any time with it. Typically measured photocurrents correspond to photon fluxes (or better "frequencies") of 10^8 to 10^12 photons per second or so (with pulsed lasers we can nowadays make photocurrents of several amps and we are doing that in certain types of accelerators).
What high energy physicists (that's what I like to call myself) are measuring are combinations of energy, momentum, angular momentum and charges (electric charge, leptonic charge etc.). You can easily verify this by reading the technical design documents of e.g. the CERN detectors (ATLAS, CMS). They are freely available to the public. You will quickly notice that high energy physics detectors are not trying to measure "particles". They are measuring energy deposition in the matter of the detectors. The patterns (tracks) of that deposition process allows us to reconstruct the energy, momentum and charge exchange between the free field (the physical vacuum) and the detector hardware.
The physics of how we get from quanta of energy to "particle tracks" was elaborated very early by Mott in a 1929 paper. You can find it online, if you want to read it. It's one of the most important papers in physics history that almost nobody seems to know about. It's the first fully worked out example of "weak measurement" that I know about. Heisenberg talked about weak measurement a couple years earlier, I believe, but he didn't flash it out theoretically. What basically happens is that we are measuring consecutive scattering processes of the original quantum that spawns ever more new quanta of ever smaller energy but with more of less the same momentum. It's the compound probability formula that connects these individual location measurements of these quanta to what seems like an almost straight line. It's basically a random walk process overlaid on a large momentum state.
There are no particles there, either. It's again just the human mind imaging something that doesn't exist. We made the same mistake twice before, when we identified heat energy with a mythical "Stoff" called phlogiston and were looking for a material carrier of energy in the vacuum, which was called "ether". The "particles" in poor explanations of quantum mechanics are just that: imaginary beasts that derive from the same material carrier fallacy. The human mind likes to imagine "stuff", even when only properties are changing. It's not limited to physics, either. In economics many people are misidentifying money (which is just an exchange quantity) with the need for a physical representation, like coins, printed notes, gold bars or even some computer code (like bitcoin). None of that is needed to transfer money and banks aren't working that way. They are simply updating account ledgers with numbers. Money is an abstract exchange of value that is assured by synchronization (balancing) of accounts. That is exactly the same mechanism that nature uses for locally conserved system properties like energy, momentum, angular momentum and charge.
So if you want to teach modern physics correctly, even at this level, try to tell students NOT to imagine things that aren't there... like particles. I admit that this kind of mental discipline probably would have to start in kindergarten and preschool... by the time we get to high school physics it's kind of too late to remove poor mental habits from student's minds.