The photoelectric effect
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- čas přidán 15. 06. 2024
- MIT 8.04 Quantum Physics I, Spring 2016
View the complete course: ocw.mit.edu/8-04S16
Instructor: Barton Zwiebach
License: Creative Commons BY-NC-SA
More information at ocw.mit.edu/terms
More courses at ocw.mit.edu
This lecturer is great, he coveys the info in a way that is actually digestible!
I admit that. I have followed other lectures, for example by Leonard Susskind (who is also a very good lecturer) but Barton Zwiebach has my preference right now. I like his gentle style.
Perfect work from this lecturer
Even though Professor Zwiebach has a strong foreign accent, I still loved this lecture since he made the lesson so digestible and explained photoelectric effect so clearly!
Actually the foreign accent helps
The foreign accent makes it clearer than an American accent imo lol
@@pubgplayer1720 Agree totally
Look who is talking about foreign accents 😅
We are given 1.5 hrs lecture on photoelectric effect. With stuff like stopping potential, saturation current, 7 graphs, requirement of photoelectric effect.
Excellent lecturer
This is great to have this opportunity to view without cost.
Just keep in mind, people (at the beginning of this video, when the Prof. discusses Hertzs’ experiment), that electrons had not yet been discovered ! 😯
12:43 My neurodivergent brain can only focus on the dust alien head on the board
That's a perfect speech!
I like mit lectures.
Excellent
Very nice ...
So nice
Thanks sir
good!
superlike for the awesome way of solve.....you are awesome sir..respect from india
Yes, he is a nice teacher , I, too, appreciate his lecture .
thats an ausome lecture i just loved it from india ❤
2π = 6 gang 20:34
should spend more time on explaining the experimental setup. How the electron energy is measured is more important than how it's calculated. That's especially true considering that measuring energy (as I understand) is used to calculate h and not the other way around as the calculus seems to show
The electron energy is measured by measuring how far the electron is deflected by a magnetic field.
It can be measured by applying reverse potential between electrodes and measuring the stoping potential
The KEmax = eVo
@@andrewstone8999 The wrong answer got more upvotes. I must be on the internet. :-)
In the exercise while calculating the speed from where did this (mec^2)(v^2 / c^2) came?
Dl Profesor! Dumneavoastra sustineti hotarat ca fotonul incident in metal, poate sa interactioneze direct cu electronul cvasuliber din metal. Si in aceasta interactiune foton-electron, explicata de Einstein, nu este obligatoriu sa se respecte conservarea impulsului si energiei, pe durata interactiunii, asa cum este explicata in cazul efectului Compton
Mr. Professor! You firmly support that the photon incident in the metal can directly interact with the quasi-free electron in the metal. And in this photon-electron interaction, explained by Einstein, it is not mandatory to observe the conservation of momentum and energy, during the interaction, as is explained in the case of the Compton effect
In 3) he says "magnitude of the current is proportional to the light intensity" but the formula gives E(electron) = E(photon) - W which is not proportionality!
Magnitude and Energy are 2 different things.
Magnitude is proportional to intensity and Energy is given as difference of photon energy and work function
Magnitude of the current it's the *number* of electrons per second. And energy it's the kinetic energy, proportional to the *velocity* of the electrons
Eu am ajuns la concluzia ca efectul fotoelectric este totusi produs prin inductie electromagnetica. Fotonul incident in metal se structureaza ca o unda stationara de mare amplitudine. Unda stationara se comporta ca un curent electric produs de o singura sarcina intro spira. La spargerea undei stationare, apare prin inductie electromagnetica un impuls electric care accelereaza sarcina din imediata vecinatate. Doar asa se asigura conservarea impulsului si energiei fotonului incident in metal, pe durata interactiunii fotonului cu electronul.
I came to the conclusion that the photoelectric effect is still produced by electromagnetic induction. The incident photon in the metal is structured as a high-amplitude stationary wave. The standing wave behaves like an electric current produced by a single charge in the coil. When the standing wave breaks, an electric impulse appears through electromagnetic induction that accelerates the load in the immediate vicinity. This is the only way to ensure the preservation of the momentum and energy of the incident photon in the metal, during the interaction of the photon with the electron.
Doesn’t this experiment prove that you can create a powerful electromagnet using metal and light?
And that you could technically create electricity using laser beams to replace what we know now as generators. Is this the zero emissions energy we’re talking about?
I don't think so. Because the current here is too little to do that. But Photo-diode does the same thing( Solar Cell ). Every one uses them.
the results of this experiment are on the atomic scale, energy on the order of 100-1000s of eV's. 1 Joule is the power to lift 1 kg 1 meter and is about 10^19 eV's. 1 kilowatt hour is over 1million joules, Its not really a straight forward way of energy production. Alternately this is basically what sun is to manufactured solar cells which is not zero emission to make them. I guess the real answer is in the details of how you do it, and if you know a way, good luck
You are far off on the energy scale. This principle is used to understand how solar cells work but the energy necessary to create a strong enough magnetic current is far too great that would defeat the purpose.
It bothers me that the energy of the photon is written when h.v, when , when h.n. When it would be perfectly normal to write h.f. Where f comes from the frequency of the photon. And then it bothers me that during the interaction of the incident photon with the electron in the metal, the conservation of momentum and energy is not respected. To obtain the energy balance, the extraction work Wex is added to the equation. Something that is a subsequent effect of the interaction of the photon with the electron in the metal. The mechanism of the photoelectric effect is based on an electric impulse of induction that occurs during the rapid damping of the standing wave, of high amplitude, constituted by the constructive interference of the wave titles from the component of the wave packet of the incident photon in the metal. The high-amplitude wave of the photon refracted in the metal appears after the contraction of the photon both longitudinally and transversely. proportional to the index of refraction of the metal, which is of the order of tens, and its refraction at 360 degrees, in the atomic environment, of high energy density. The stationary wave, of high amplitude, propagates on the circle of the Rfm metal photon radius, with a speed of C/137 (m/s) and behaves like an elementary electric charge, which produces a current in the coil. When the high-amplitude standing wave breaks, the electric impulse appears, through electromagnetic induction, which accelerates the electron in the immediate vicinity.
Yes, that was a lot of nonsense. ;-)
I came here to understand class 11 chemistry.😝
Go back to your textbook now
@@ChessCube2 The whole problem is my text is super-confusing.
and were blessed with so much more👍
Try to derive the schrödinger equation its possible using class 11 12 physics
@@vasdgod first you learn to write schrödinger's equation
Are there lectures in undergraduate or graduate programs?
Mohammad Ali undergraduate I believe
Remember the experiment where you take a charge from infinity to measure the Electric field? If 2 charges are separated by very long distance, because of the minimum energy possible, does the Electric field have a limit?
The electric field gets weaker as the charges are being separated.
@@lepidoptera9337 Mathematically, yes. But what if the charge is a light-year out?
@@putinscat1208 Then you will have to wait a year. ;-)
does MIT advocate the memorization and examination on constant values? is the value of h not provided on tests/exams?
+nickt The easiest way to find out is to look at the exams that are published on the full OCW course site here: ocw.mit.edu/8-04S16. Formulas are provided.
thanks. btw will the answer keys to exams and assignments be released in the future?
That is up to the discretion of the instructor. If the course currently uses those exams and assignments, the instructor is highly unlikely to give answers.
he's good but expected more from MIT lectures!
Undergrad lectures are pretty even among all academic institutions. There is only so much an average student can absorb. You have to keep in mind that you are typically taking four to six courses in parallel and there are weekly homework assignments for at least those that you have to pass to get your degree.
9:42 to 9:49 You said intensity is function of frequency in black body radiation. But in photoelectric effect (PEE) energy of electrons depend upon frequency rather than light. Why this two different thing_ if intensity is function of frequency then in PEE energy of electron should depend upon both frequency and intensity. Explain this!
Intensity is a function of frequency in black body radiation, not in every kind of radiation. In the photoelectric experiment we can vary the intensity without varying the frequency, we have the tools to do so.
How does one know when things are relativistic vs when they are not?
Roughly when the kinetic energy is on the same order as the rest energy, then it starts to become relativistic.
is that equivalent to saying if the speed is in the order of magnitude of the speed of light? (sorry I very rusty on some of my physics, but not rusty on my linear algebra I believe)
Yes, roughly starting from 0.1c and up, you may want to use special relativity.
Things are always relativistic! But for speeds much less than c you can use the approximation which is ordinary classical theory and get very accurate results - you can get to the moon that way!
as a highschool student i have to work this for my exam. it all exist in our book. isn't it too much for grade 12?
This is university level.
This is in my 6th grade book.
I'm doing this in year 12 too
No it's not if you are in india
Love you sir from INDIA 🇮🇳
I am INDIAN TOO!!!
I am Indian too
My country wants this lecture at highschool...im bored of my mother language because of working hard at it so im here...kolay gelsin...
Is this really University Physics?
Yes, albeit the American undergrad version is often slower than the European one. If you want to go faster, study in England or Germany. Don't know about France (never been in a French university), but it's probably more intense than the US as well.
I assume this is the first lesson in MIT because this seems like easy stuff you do when you're 16 in the UK so if you are 18 and still doing this i hope it gets more intresting than just this.
If you've ever looked at any of the MIT OpenCourseware material, you should know that the lectures are the easy part, and that the difficulty lies in the homework assignments and tests.
In contrast, in shitty universities, lectures are the difficult part and homeworks are the easy part, even though many students will fail to get through even the easiest possible assignments that are almost exactly like the textbook's example problems.
@@lorax121323correct, lectures are supposed to set you up for self-study via assignments and reading
You are doing a few things that you did in high school again in beginners courses in university. Double slit, photoelectric effect, Newtonian mechanics (but it rapidly becomes Lagrange and Hamilton)
@@lorax121323 We generally had a 50% homework requirement. I was always around 60-80% except in continuum mechanics. That crap just beat the hell out of my brain. I hate stress tensors with a vengeance. ;-)
Could the simultaneous be a number?
Me after watching this (high schooler from india preparing for jee):
So this is what they teach even in mit in first year huh??
not in the first year, but u can take some basis
Bro u are kid...right now......so don't take these great lectures............ 😏......
And I am also from india.....and Zwieback is a great professor.....think before saying something about any teacher.....
Yes, but this is the easiest of the stuff that you have to learn in the first year. The first year is generally not too hard in terms of intellectual difficulty, but you aren't getting much sleep because you have homework assignments in four to six parallel courses that are due. The second to fourth years have less homework but it's considerably harder material.
Am watching from Palestine✔🙂
no one asked
Could be that the being itself be the 1 that precedes any mathematism...?
o unlikes woww
We are reading it in class 12th😂
As you should. The photoelectric effect has been part of the high school curriculum for at least 40 years.
Silly. It requires photon's energy to be split based on some hidden variable (work function). But most importantly it ignores the conservation of momentum, which postulates that the energy of colliding bodies is distributed equally between the bodies. The work function mechanism is fantasy considering that in gas the absorption of light works over windows of particular frequencies. Einstein did not uncover'or explain some fundamental relationship of matter. My guess is that a photoelectric cell's efficiency will level off at 50% in deference to the conservation of mo. My bet is that the energy of photo-electrons will not increase linearly with impinging photons' energy and do so *forever* -- as the professor's presentation suggests.
@Hugh Jones
You can talk the talk ...
And what exactly makes you more qualified than a MIT professor?
@@achalsinghal7115
Because you (and maybe others) cannot respond on the basis of merit. A person could spend a lot of money getting a law degree but that does not mean he/she must win every case. In your pathetic case, you would think one must accept the lawyer's statements without rebuttal. Fool and his money will soon part.
what is your 'bet', 'guess' based on? My guess is that a bet or guess of something will never be accepted as proof to anything, not to mention a scientific law.
interesting, would like to know more about it. Do you have a website?
we can solve numerical in a better and easier way without using hbar and etc
Yes but hbar is much more useful in Quantum mechanics.
This series is better than anything on Netflix. It's almost as interesting as a tweet from President Trump.
Love this, I am currently getting my 7th Ph.D, this is now my Quantum Physics Ph.D