8.03 - Lect 13 - Electromagnetic Waves, Solutions to Maxwell's Equations, Polarization

Electromagnetic Waves - Plane Wave Solutions to Maxwell's Equations - Polarization - Malus' Law
Assignments Lecture 13 and 14: freepdfhosting.com/924d1cc8e9.pdf
Solutions Lecture 13 and 14: freepdfhosting.com/8604fe3059.pdf

[@emeraldeyes9565]

An interesting historical fact is that Maxwell's formulation was composed of 20 equations in 20 variables which Heaviside showed could be reduced to just 4 equations in 4 variables. These are the ones taught today.

[@schmetterling4477]

One can write the whole thing in tensorial form in a single equation.

[@kyle5555]

@@schmetterling4477 fuckkkk.. lol I’m struggling with the first one still

[@keisi1574]

@@schmetterling4477 I'm working on being able to express it with .33 of an equation.

[@alirezanabavian771]

@@keisi1574 only if humans lost 8 fingers then your research would be useful

[@raulacosta1594]

Very good vibes from this teacher, I don't know much English but I interpret technical questions perfectly. I am not a student, I am just a madman who invents things in the small laboratory at home and steals a little knowledge of the internet and the good people who provide it on the net. Thank you very much teacher.

[@alirezanabavian771]

You're very smart and unique

[@dc1049]

All these lecture series are a gold mine, youtube is a more effective method of teaching than sitting in class ever will be. Simply because of the luxury of the rewind button... I wish the academic infrastructure acknowledged that fact and stopped throwing money away on poor lecturers (who might know what they're talking about but have such poor delivery skills). In the words of Feynman: "It’s impossible to learn very much by simply sitting in a lecture, or even by simply doing problems that are assigned." This is why I believe class time should be used strictly for questions and discussion... a two way road, not a one way force feed of information. The feeding of information can be done at home through tools such as KZbin and amazing lecturers such as Walter Lewin who perfected the craft and put their heart and soul into it. As opposed to tenured professors who sit on their research and could care less about the students they need to teach, or the quality of their lectures.

[@lecturesbywalterlewin.they9259]

+D C I know many tenured Professor (I also had tenure) who do care about teaching. However, few are talented teachers.

[@ms-uj3qe]

+D C Really? Let`s stop all physics classes, because walter lewin has done it better on youtube... Are you serious? Just because you study on a shit university that doesn`t mean that there are no good, passionate professors out there.

[@ms-uj3qe]

+Man, I don`t even have an opinion *Because you think your university is shit* is more like what I was trying to say.

[@dc1049]

Man, I don`t even have an opinion You are quite correct, perhaps I was too harsh with my opinion of some professors. My main problem is with the modern academic structure as a whole sir. I do not think the system of sitting in class while listening to a professor monologue through a discussion is very effective. As I stated before, I think Richard Feynman already pointed out exactly what the problem is.

[@das250250]

D C yes indeed , being a good teacher and a good professor aren't necessarily the same ..teaching is a real skill

[@efeguleroglu]

Thank you for sharing your lectures with us. You're a great teacher Walter Lewin.

[@jacobvandijk6525]

Walter, it's a shame there isn't a Nobel Prize for Teaching.

[@outrospection4all]

or at least made an FRS

[@srabanisamanta1599]

Dont worry great person dose not need nobel prize.

[@hrkalita159]

Noble prize is unlucky as these person (Hawking's, lewin) don't touch it.

[@mohammadmursalin6817]

All Jeff Bezos would have to do would be to create the Bezos prize for Teaching and Educating and things would be fine............but nooooo...................Dr Evil had to piss all that money on his space mission.

[@munirkofa4783]

Jacob van Dijk sincerely speaking

[@aibi-rv2mm]

These students have been so lucky to have attended your classes. And I still enjoy learning from your dynamic classes. They are just fantastic. Thank you, Professor Walter Lewin!

[@lecturesbywalterlewin.they9259]

Glad you like them!

[@saulsavelis575]

@@lecturesbywalterlewin.they9259 Maxwell did not postulate, he heard and even cited Faraday who guest correctly that light is EM phenomenon

[@deathtotruthers1]

How is it possible for Lewin to make these esoteric, ridiculously difficult concepts understandable? Shame he retired - though he deserves it. He was a brilliant educator.

[@DJRobbie54]

That was A Nice Lecture on Electromagnetic Waves Polarization, Professor Walter Lewin. The Math was a bit hard on me, but I began to see it in a spiritual Realm of Quantum Entanglement in the Cosmos of the Universe. This is the first time I have seen any of your lectures, Very Well Done. I look foreword to watching more of your videos, to learn about Electromagnetic Waves. I Like your style of teaching us this amazing subject. It was a lot of fun to watch, and learn, and see your demonstrations that you perform to your students, they had fun to. I like teachers like that, who can have fun, but, be serious at the same time of what he or she is trying to teach the class, that makes learning easier. That encourages students to want more. I also know this was an old Video that was uploaded back in 2015. To me it is a breath of fresh air of learning of a subject I did not understand when I was a young man back in the day. I hope you're still in good Health and still teaching your students. I have become one of them, at 68 years old. Which, go's to say, your never to old to learn. Thank You Professor. January 11th 2023. PSS, Check out Royal Raymond Rife's Discoveries, Back in the 1920's, I think you'll find it very enlightening.

[@pranjaldubey3384]

we read electromagnetic waves today in class and im happy to have found this lecture here today~

[@misspandora432]

Dear Professor Lewin, At first, I would like to thank you for all the works you made available on KZbin with your lessons. It's terrific. I learnt physics 30 years ago where I was quite successful, and for some reasons, I didn't make a career in Physics. Looking at the way you have done this marvellous job at the MIT, I am almost able to quit my job and everything, and to come back to the University, even to the MIT! Second, in your lecture #13 from MIT 8.03 video, you talk about the way that a human (you !) can see the polarized light and how to recognize it. Could you be kind enough to light my brain about this subject? Dear professor, thank you very much for what you have done in the way you did it, it is "extraordinaire". Best regards, Marc André. Paris, France.

[@Leptus87]

Great lecture, conducted with briliancy and passion as well!

[@danielkinyanjui5296]

Professor Lewen, you show such a deep understanding of the subject matter that goes beyond rote. You would be perfect for Africa! Thank you.

[@user-dg1wq4nd7h]

Dear Professor Lewin, I hope this finds you well. I am a senior in high school and absolutely love your lectures. I have been following your talks and KZbin page for over a year now and, as it’s my last year of high school, have embarked on an ambitious task. I am endeavoring to reconstruct the electromagnetic wave transmitter/receiver demonstration you present at 1:00:07 in this video. I have exhaustively studied the theory and searched the far reaches of the internet and my school for answers on assembly methods, but have yet to find a satisfactory idea or construction methodology. I now turn to you for any guidance you have the time to give me. Any crumb of information would be greatly appreciated, I thank you for all you have taught me and all I have to learn from you. My best, -Henry

[@lecturesbywalterlewin.they9259]

I can't help you as I am not an engineer

[@technocrat711]

Had it about 40 years ago. Enjoy the lecture. Light bulb burning is something few can forget.

[@arkadiptaghosh99]

you have just opened my eyes...I am seeing what I was not able to see it before...Thank you professor..:)) Respect

[@sidereal6296]

Mr Lewin, I’m a freshman at MIT right now taking this class, on this lecture. I love my professor but the way you teach, connect everything together, and give meaningful historical context, is simply inspiring. Thank you for uploading these to KZbin

[@CurrentlyObsessively]

Congrats on graduation!

[@sundaranarasimhan58]

Excellent quality of presentations. I wish I was your student. Love from India.

[@fatihorhan9355]

Great lecture! Thank you for your great uploads.

[@akshatparwani4961]

i was struglling with college level physics. your lecture made it very easy

[@emmanueloverrated]

I wish I had this professor when doing this course... I had this guy (professor?) who was more interrested in research than to teach and made me hate this matter... Better than not failing the course, I would probably loved electromagnetism and been pretty good at it.

[@spdas5942]

Excellent teaching , sir . Hats off !

[@lecturesbywalterlewin.they9259]

Keep watching

[@Andreasskaliontas]

17:05 that phone call is written in the history of Physics Lectures by this great video

[@sumansaurav1945]

This is one of the best lecture given by you amazingly super

[@lecturesbywalterlewin.they9259]

:)

[@MarkFunderburk]

I meant to go to bed 2 hours ago but I can't stop watching this. Thank you sir for keeping me loving physics. I was getting dragged down during physics 2 this past semester and these lectures have helped turn that feeling around.

[@lecturesbywalterlewin.they9259]

:)

[@pad_52]

Dear Sir Lewin, First I want to express my gratitude in sharing for free, those pieces of art that are your Physics Lectures. Your lessons helped me more than once in my engineering career and never stops to help: not just for understanding the argument, but also thanks to your teaching enthusiasm that is so contagious that my learning enthusiasm benefits. I can’t believe in my eyes when all your lectures disappeared from the Internet! Thanks for putting them online again. I’ve a little question: in 1:09:54 you said that you are able to teach a human to see a polarized light like a bee :) Will you ever do a lesson about this? I wish you all the best, Kind Regards. Paolo

[@lecturesbywalterlewin.they9259]

google Haidinger's brush

[@GuilherHast]

Thank you for the question. Thank you for the answer.

[@promethialcronus]

​@@lecturesbywalterlewin.they9259 Does maxwells equation have it all.Can there be more than just the EM radiation .with just 4 equations solved you can make yhe whole world feel the awe and not ask another question just for the sake of readers or whatever or critics maybe.

[@mobile2]

interesting lecture. studied electronic engineering, work as cellular radio network engineer. Since GSM1800 in 1997, cellular antenna has used linear +45/-45 slant polarization as people hold cell phone in slant orienatation

[@p0k7lm]

Thanks for the lecture, this will supplement my two Maxwell's volumes to for a better understanding of the E and B fields.🎓📝📚📐

[@puneethprahalad7386]

Walter Lewin and H.C.Verma are legends who make you fall in love with physics

[@kingg283]

I have seen some youtube lectures also from Yale. Like this it is extraordinary. Think about if only masterpieces like this will be used for lecture. It is meant globalisation of knowledge then. What ist local school then? Will they die? Thanks anyway to Walter for this passionating Lecture.

[@federicoborsotti8947]

The representation at 26:12 is a classical representation of EM waves. But if the strength of the electric field is c (speed of light) times stronger than the magnetic field, and if the magnitude of the vectors in the representation represents the strength of the respective fields, does that mean that in a more "faithful" (though clearly unmanageable) representation the arrows used to represent the magnetic field should be c times shorter than the arrows used to represent the electric field?

[@anassbensaid9197]

I always like the physics and I'll thanks for this video :) sir

[@naturalscience2022]

This video inspired me personally to do a demo E&M wave for my grade 12 students in Cambodia. Physics is magic and Beauty.

[@lecturesbywalterlewin.they9259]

super, keep it up!

[@studywithjosh5109]

I have thought about physical situations where there would be a pattern moving faster than the speed of light before I knew any concrete physics and now I understand I was thinking about phase velocity. It makes a lot of sense now!!!!!! I was so confused before because I thought that nothing could move faster than light.

[@fupa_lvr]

What a Masterclass

[@perfectlyimperfect6849]

Sir your lectures give us real feel of physics Thankyou sooo much for these gems Just enjoyed your lecture🙏😊

[@lecturesbywalterlewin.they9259]

It's my pleasure

[@jpdemont]

Awesome teacher.

[@filipecardozo]

This is gold. Thank you for existing

[@lecturesbywalterlewin.they9259]

:)

[@asbargathi]

PERFECT. thank you sir, I'm really happy for this good job

[@lecturesbywalterlewin.they9259]

You are welcome!

[@kolithawarnakulasooriya3069]

This is wonderful

[@davegeorge7094]

He draws a dotting line like the best one handed drum roll! He's second to none with hand speed, anyone disagree?

[@Sixalienasa]

it is in fact the way the board works, if you press the chalk at a certain pressure and direction is bounces on the board giving that effect.

[@davegeorge7094]

No, I think it's a skill. watch it again.

[@Sixalienasa]

I have watched several people do it, and yes there is skill attached too.

[@lecturesbywalterlewin.they9259]

Watch this video kzbin.info/www/bejne/qJLYo59qqJWjoLc

[@lecturesbywalterlewin.they9259]

watch this video kzbin.info/www/bejne/qJLYo59qqJWjoLc

[@inthenameofjustice8811]

His last words in this cracked me up. "Who wants a black eye? See you next Tuesday." Or, put another way, 'Who wants a black eye? C.U.Next.Tuesday.' Though I am sure this was an accident I still laughed like a drain.

[@RD2564]

One of the beautiful things about this is how WL does not take any shortcuts with notation, which is helpful for viewers learning the subject. PS: "Don't even THINK of using a left handed coordinate system." Awesome performance.

[@otiebrown9999]

Good logical presentation.

[@saskiavanhoutert3190]

Polarized vetor-rotation can be used for rotors of planes, to avoid birdstrikes perhaps, just a notion, thanks for lectures

[@lecturesbywalterlewin.they9259]

:)

[@sanjoykumarrouth6410]

After viewing these wonderful lectures every student is going to enjoy physics more.

[@das250250]

At the end they did not applaud but they looked tired and uninterested , i find this incredible , one of the most enthused lecturer's i have ever seen on here , i wish i had such a teacher at my uni. I would have applauded ..to thank him

[@Saptarshi.Sarkar]

What happens to the oscillating magnetic field after light passes through a polarizer? Is it unaffected?

[@lecturesbywalterlewin.they9259]

B field will be affected as the B field in the EM wave will be perpendicular to the E-field.

[@odal6770]

I have the impression that Maxwell's Laws serve a unique goal, and that is to give empty space all the properties of matter, except visibility and physical substance. In other words, it is the ether formulated mathematically.

[@siddheswarmondal7764]

Nice... Sir thanku so much 🙏🏻🙏🏻

[@vasudevannambudiri5916]

A grand Salut to you Sir.

[@sohammukherjee8877]

I always had a question when writing the expression for E field we took it along x direction and the wave in z direction. How do we know from the Maxwell's equation that E and B will be perpendicular and the wave will be travelling in the direction of E×B

[@lecturesbywalterlewin.they9259]

I cover all this in my 8.03 lectures.

[@gioegiogcbr]

Why is the antenna of the receiver longher than the transmitter, shouldn’t they be same to capture that specific wavelength?

[@atruety]

I just love you sir 😍😍😍😍😍😍😍 Love from India 🇮🇳🇮🇳

[@ostora94]

why does the electric (or magnetic ) field vary spatially only with the direction of propagation of the wave (i.e. if the wave propagates in the "z" direction "E" is only a function of (z,t) ) ?

[@lecturesbywalterlewin.they9259]

like water waves, they propagate and thus E is also a function of the direction of propagation.

[@oningsingson5672]

Excellent Teacher🎉

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@anisand]

What about the long-known adverse biological effects of electromagnetic waves? A vital caveat to any lecture on this subject surely?

[@kristifrroku3170]

The best ever

[@tjcanno]

Thank you for this, Dr. Lewin. Very helpful. Please, if you would , explain to us how we know that the E field and the B field are in phase? I expected the peak/trough of the E field to align with the B field crossing through the zero line, and then the same with the E field crossing through zero where the B field was at a maximum/minimum. Could they not be out of phase by pi/2?

[@lecturesbywalterlewin.they9259]

they have to obey Maxwell's eqs. However, there are solutions to M's eqs which allow for different phase differences

[@srikanththota648]

At 1:03:26 the hand absorbed the electromagnetic radiation. That's very interesting. How does this happen? And, what wavelengths of radiation can the hand can pass through it? In General, if the electromagnetic wave hits an object, based on what characteristics of the object can we say if the radiation can go through it or not? And, lastly is this explained in any of the lectures?

[@asbargathi]

water can greatly weaken the microwave, like the rain destroy the satellite signal.

[@dwjs_]

Hi sir, I have just finished watching your 8.02x course. In that course you derived integral form Maxwell equations. In this video you used differential form Maxwell equations. I want to know whether you have a video which explained differential form Maxwell equations in details?

[@lecturesbywalterlewin.they9259]

Look up the differential form online.

[@KunalSingh-my5nd]

Sir, what is the way which you have learnt to tell wheather a light is linearly polarized? You refer to that at 1:09:50 into this 8.03, no 13 lecture. Please share I am keen!!

[@lecturesbywalterlewin.they9259]

I use my linear polarizer. Google Haidinger's Brush.

[@boshooda1941]

are there high res versions of these lectures that can be posted?

[@CurrentlyObsessively]

These are recorded in the 90s. So I would assume no. This IS high def for that era of cameras. I remember them well...

[@huonghuongnuquy7272]

what a great lecture ! Thank you very much.

[@YannisAlepidis]

At 1:07:30 why the average value of cos2(x) and not the integral of cos2(x) from 0 tο 2π?

[@kevinradl1462]

There is something I don't quite understand about EM waves: My professor told us that electromagnetic waves are caused by accelarating charges and the Wave can be understood as the 'information' of the changing electric and magnetic field traveling through space. How can we detect them over such long distances and why don't they lose intensity proportional to 1/r^2 ?

[@lecturesbywalterlewin.they9259]

they spead out like a spherical balloon and YES the intensity goes down with 1/r^2. The EM intensity of the Sun goes down as 1/r^2.

[@pakistan010203]

WHAT IS NAME OF THE TRANSMITTER WHICH IS CONNECTED TO THE DIPOLE ANTENNA ? CAN ANYONE PLEASE TELL ?

[@robelabera8770]

Am I the only one who thinks experiments on these lectures have a vibe of a magic show?

[@sonukadusman4574]

I love lewin sir

[@davidmendizabal9892]

33:14 at this point you got my undivided attention. OMG

[@soumyamishraCrazyZaynster]

this is an out of context question but sir would you please explain how the useful power of the AM wave lies in its side bands and not in the modulated carrier?

[@lecturesbywalterlewin.they9259]

+Soumya Mishra I don't know. PLease look it up on the web. Google!!

[@stargazer7644]

The carrier isn’t modulated. The sidebands contain the modulation. If you remove the carrier, you can put that “wasted” power into the sidebands. Thats how SSB and DSB works.

[@geminijake7398]

1:36 but isnt an electron and/or a proton a magnetic monopole? Im so fascinated with this subject matter, just trying to wrap my head around it. Awesome stuff

[@lecturesbywalterlewin.they9259]

they are electric monopoles. Magnetic monopoles do not exist.

[@fisicaematematicacomjean]

Even isolated eletrons seems to present an intrinsic magnetic dipole.

[@shubhamtalks9718]

professor, how can humans recognise polarised light and the direction of polarization under ideal conditions?

[@lecturesbywalterlewin.they9259]

google Haidinger's Brush

[@powertube5671]

Hi professor Lewin. I love your videos. I am taking meticulous notes. Here's a question. What would be the wave function of the chalk when you make those dotted lines. It's obviously alternating stress and release of the the chalk with just the correct angle of the chalk. :-)

[@lecturesbywalterlewin.they9259]

there is no wave function

[@abhiksasmal3304]

Professor, when we write Maxwell's Equations in terms of line integral and surface integrals, we talk about E and B fields that penetrate through a surface. Or in other words, we think like- what will be the line integral of E along the edges of 'this' surface if 'that much' flux changes through the surface. But if we write the equations in terms of curls and divergence, we come to know how the E and B fields are related at every point in space. Am I correct ? Is it true that Maxwell's Equations in curl and divergence form describe these fields at every point in space but same Equations written in integral form can't do the same ? Thank you for teaching us with these amazing lectures

[@lecturesbywalterlewin.they9259]

hyperphysics.phy-astr.gsu.edu/hbase/electric/maxeq.html

[@pavankalyan-zi6ei]

Thank you, Professor, for making my life ambiguous😅.

[@sunyue1909]

Dear Prof. Lewin, at 42:20, the line you draw via the origin looks more perpendicular to the k vector, doesn't it? On this line, k = 0, because it is on the origin, then k dot r = 0 (not k perpendilular to r).

[@anon6514]

Maxwell surely was a genius. I always preferred to remember them in their integral form. I remember you covered that in 8.02 Although, in the differential form, it's easier to see how a wave emerges. Had to pause the video to process the maths at times but I understand the subject much better now. Thank you. Amazing work.

[@lecturesbywalterlewin.they9259]

In 8.03 I use the differential form to derive the EM plane waves and the speed of light!

[@TheKansi2]

Sir I learned that we use electromagnetic waves to communicate wirelessly and electric field exist due to location of charge and magnetic field due to movement of charge. What I don't understand is that how can we communicate someone in free space ? According to web. there are about 10 atoms per cubic centi-meter. Doesn't that mean there are way less charge for E. and B. fields to do their thing therefore wave to propagate ? what did i miss or misunderstand ?

[@lecturesbywalterlewin.they9259]

There are frequency limitations which is what all radio astronomers know. use google

[@krishnapun2174]

fantastic

[@babyknifexd5307]

Sir how much voltage was induced by receiver? and what kind of bulb should i use to demonstrate the existence of EM wave? I mean the wattage of bulb, rated voltage etc(12v or 24v etc). Tnx sir.

[@NuVids2025]

Did you ever find the answer?

[@Silvertestrun]

Ty

[@babuj6949]

sir, at 38.03 minutes: as of my understanding. EM wave is moving in K- direction (because k- represents propagation direction), then what r- represents. i mean certainly wave is not moving in r- direction. wave is moving in k- direction. what way i can understand about r-direction?

[@lecturesbywalterlewin.they9259]

General form: direction is in an arbitrary direction r.

[@rgudduu]

E field at r (location or position), of a wave moving in k direction. E.g. E(x,y,z,t)= xCap E0 cos(wt-bz) Then say, we want to find E at (x,y,z)=(2,1,5), of this wave travelling in z direction at some time t0. Here r=(2,1,5), k= z direction.

[@lounesbenali4889]

Wow I am just dazzled !

[@skahatoad]

thank you so much for this! wow

[@lecturesbywalterlewin.they9259]

you are welcome

[@physicsenthusiast427]

how to get into cambridge university

[@lecturesbywalterlewin.they9259]

Apply to Cambridge. UK. It's very tough to get in though, about as tough as MIT and Harvard.

[@Stutteringjohnfan2015]

Fun fact about the lecture: this was filmed 17 years ago

[@mastipathsala912]

Sir if a capacitor connected to a battery and capacitor charged fully then what displacement current will be generates? ?

[@lecturesbywalterlewin.they9259]

watch my 8.02 lecture in which I cover displacement current as a function of time

[@AnjanakushwahaKushwaha-qj4oq]

Sir , the length of wave in y direction /wavelength multiply by c , this equation I give to the chatgpt but it say it is "wrong ".

[@lecturesbywalterlewin.they9259]

what I wrote and said is correct

[@AnjanakushwahaKushwaha-qj4oq]

Explain it in better

[@AnjanakushwahaKushwaha-qj4oq]

​@@lecturesbywalterlewin.they9259 sir please

[@lovesharesucceed4736]

I think the academic curriculum must be reframed to incorporate these online lectures.

[@gbmillergb]

I might get a few test questions right in his class if they are True/False or multiple guess... I mean choice.

[@aiswaryanarayanan7269]

Thank you sir.....

[@lecturesbywalterlewin.they9259]

Most welcome

[@no_se_nada_de_nada]

this has not subtitles :(

[@iskraivan7431]

Thank profesore!

[@schmidtzcargolbull]

Is there a lecture on the "displacement current" addition to Ampere's law? I've only every seen the mu0*I notation

[@lecturesbywalterlewin.they9259]

YES in 8.02

[@anthonyguerrera191]

Don’t u usually subtract y term when computing determinant for cross product

[@dr_rich_r]

At 4:53; he accounts for the minus by doing the 'criss-cross' in the wrong order: upper right to lower left minus upper left to lower right.

[@monkerud2108]

As measured with clocksofc

[@marcelinobartoletti3259]

Hello sir, if the electromagnetic wave is consists of two fields (electric field and magnetic field) that is perpendicular to each other, then why is the receiving antenna with a light bulb can't receive if it is in horizontal position opposite to the transmitter's antenna? (Is it only the electric field induced a current from the receiver and not the magnetic field?)

[@lecturesbywalterlewin.they9259]

the answer is Maxwell's eqs.

[@marcelinobartoletti3259]

Thank you very much sir Walter Lewin 🥰

[@TheKansi2]

Sir, I have an idea and it's just a thought..so my question is; Can we create controled electromagnetic field to change the characteristics and behaviours of a specific area of earth in a certain moment so any incoming earthquake lose some amplitude ?

[@lecturesbywalterlewin.they9259]

How would you do that? use Google and ask Quora.

[@srikanththota648]

At 48:58 from the geometry how come k/ky?

[@lecturesbywalterlewin.they9259]

:)

[@srikanththota648]

Hello Dr. Walter Lewin. Thanks for your response. I solved it myself. Now I understood it.

[@arkadiptaghosh99]

why crossed polarisers turn non polarized light into darkness????

[@lecturesbywalterlewin.they9259]

use google

[@m.servat3447]

Dear Prof. Where can I post my questions?

[@lecturesbywalterlewin.they9259]

here! always refer to the lecture and to how many minutes into the video