The photoelectric effect

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

[@devinpatterson1292]

This lecturer is great, he coveys the info in a way that is actually digestible!

[@TheVincent0268]

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.

[@user-fb6no8se4r]

Perfect work from this lecturer

[@amritsagarkar7899]

We are given 1.5 hrs lecture on photoelectric effect. With stuff like stopping potential, saturation current, 7 graphs, requirement of photoelectric effect.

[@haydenyuan4720]

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!

[@athul_c1375]

Actually the foreign accent helps

[@pubgplayer1720]

The foreign accent makes it clearer than an American accent imo lol

[@fjs1111]

@@pubgplayer1720 Agree totally

[@abdulwasaye8511]

Look who is talking about foreign accents 😅

[@sneakypress]

Just keep in mind, people (at the beginning of this video, when the Prof. discusses Hertzs’ experiment), that electrons had not yet been discovered ! 😯

[@jameshay8595]

This is great to have this opportunity to view without cost.

[@sebjuv123]

Excellent lecturer

[@rimshashafique2757]

In the exercise while calculating the speed from where did this (mec^2)(v^2 / c^2) came?

[@mingyuanshao7876]

That's a perfect speech!

[@leopardtiger1022]

I like mit lectures.

[@JettixX]

Excellent

[@Mdsahil-zg7bn]

thats an ausome lecture i just loved it from india ❤

[@nathanherling9836]

Very nice ...

[@manudehanoi]

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

[@andrewstone8999]

The electron energy is measured by measuring how far the electron is deflected by a magnetic field.

[@athul_c1375]

It can be measured by applying reverse potential between electrodes and measuring the stoping potential The KEmax = eVo

[@kabandajamir9844]

Thanks sir

[@kabandajamir9844]

So nice

[@zhanyichng6044]

2π = 6 gang 20:34

[@yoavtamir7707]

good!

[@arindamgoswami4587]

superlike for the awesome way of solve.....you are awesome sir..respect from india

[@Photonphantom]

Yes, he is a nice teacher , I, too, appreciate his lecture .

[@adriangheorghe2327]

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.

[@cafe-tomate]

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!

[@hemanthsaikumar]

Magnitude and Energy are 2 different things. Magnitude is proportional to intensity and Energy is given as difference of photon energy and work function

[@brendastephanie1403]

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

[@putinscat1208]

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?

[@nicktohzyu]

does MIT advocate the memorization and examination on constant values? is the value of h not provided on tests/exams?

[@mitocw]

+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.

[@nicktohzyu]

thanks. btw will the answer keys to exams and assignments be released in the future?

[@mitocw]

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.

[@mohphyyu]

Are there lectures in undergraduate or graduate programs?

[@iaexo]

Mohammad Ali undergraduate I believe

[@kaushaljain5999]

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!

[@green0563]

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.

[@e7hikful54]

Hey 1ts William Francis

[@beautyofeverything7444]

I came here to understand class 11 chemistry.😝

[@ChessCube2]

Go back to your textbook now

[@beautyofeverything7444]

@@ChessCube2 The whole problem is my text is super-confusing.

[@youcanknowanything8489]

and were blessed with so much more👍

[@vasdgod]

Try to derive the schrödinger equation its possible using class 11 12 physics

[@Krish_202]

​@@vasdgod first you learn to write schrödinger's equation

[@brendastephanie1403]

12:43 My neurodivergent brain can only focus on the dust alien head on the board

[@marialiyubman]

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?

[@devnampriyapriyadarshi1331]

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.

[@raatkin6329]

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

[@dontacomx3794]

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.

[@pratikchaudhari5371]

Love you sir from INDIA 🇮🇳

[@amritkumarpatel5717]

I am INDIAN TOO!!!

[@abhinandanmehra7765]

I am Indian too

[@akshatsharma8151]

Is this really University Physics?

[@iozarslan]

My country wants this lecture at highschool...im bored of my mother language because of working hard at it so im here...kolay gelsin...

[@sentimentalperson8793]

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?

[@mwaleed2082]

This is university level.

[@MrBeen992]

This is in my 6th grade book.

[@KhawOfficial]

I'm doing this in year 12 too

[@isohel9889]

No it's not if you are in india

[@brandomiranda6703]

How does one know when things are relativistic vs when they are not?

[@klmnts]

Roughly when the kinetic energy is on the same order as the rest energy, then it starts to become relativistic.

[@brandomiranda6703]

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)

[@klmnts]

Yes, roughly starting from 0.1c and up, you may want to use special relativity.

[@lsbrother]

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!

[@hadlevick]

Could the simultaneous be a number?

[@ayush3717]

We are reading it in class 12th😂

[@StarNumbers]

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.

[@StarNumbers]

@Hugh Jones You can talk the talk ...

[@achalsinghal7115]

And what exactly makes you more qualified than a MIT professor?

[@StarNumbers]

@@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.

[@gkollias14]

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.

[@aryasingh8173]

interesting, would like to know more about it. Do you have a website?

[@felixfrandes6136]

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.

[@lorax121323]

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.

[@mukundanm2666]

Me after watching this (high schooler from india preparing for jee): So this is what they teach even in mit in first year huh??

[@sanchescosta2398]

not in the first year, but u can take some basis

[@babes7797]

Bro u are kid...right now......so don't take these great lectures............ 😏......

[@babes7797]

And I am also from india.....and Zwieback is a great professor.....think before saying something about any teacher.....

[@dr.shahedjaberthenerd8544]

Am watching from Palestine✔🙂

[@skiraf]

This series is better than anything on Netflix. It's almost as interesting as a tweet from President Trump.

[@hadlevick]

Could be that the being itself be the 1 that precedes any mathematism...?

[@x-girlsobasso6278]

o unlikes woww

[@e7hikful54]

Do you know how to speak? I have a thinktank called ANU. MY NAME IS WTP REALLY. 409 S

[@sharmashubham432]

we can solve numerical in a better and easier way without using hbar and etc

[@aadityaphadnis8399]

Yes but hbar is much more useful in Quantum mechanics.

[@TastyTesticlesTube]

Love this, I am currently getting my 7th Ph.D, this is now my Quantum Physics Ph.D