Polarization, Rainbows and Cheap Sunglasses

Prof. Lewin gave this talk for kids and their parents. He covered the concept of waves, polarization and did demonstrations at the Brewster angle to create 100% linearly polarized light. He also demonstrated that the light from rainbows is close to 100% linearly polarized and that the blue sky at 90 degr from the Sun is 100% linearly polarized. Everyone was given 2 linear polarizers which they could keep. This allowed them to check later outdoors what was demonstrated in the lecture hall.

[@ron2788]

Mr. Lewin your lectures provide a personal connection with everyone that is listening that is unmatched with any other professor. Thank you for all your hard work and dedication toward science!

[@lecturesbywalterlewin.they9259]

+Matthew Ardito-Proulx Thank you for your kind words.

[@bretjackson4829]

A physics Professor that explains physics so people can actually understand without having to go to multiple resources, brilliant!

[@gurjindersingh8820]

Omg fully understandable,fully enjoyment and what a moment when little ask a question with the idea of two prism , fantastic lecture . Thank you Sir .

[@tarekabdulfattah3458]

You are the best ever professor i have seen All respect, appreciation and love to you from Lebanon 🇱🇧

[@lecturesbywalterlewin.they9259]

Wow, thank you!

[@jontyroy1723]

It was mind blowing when that little kid came up with the idea of combining two prisms! :O Such a creative mind! And as always, it was a beautiful show professor. Thank you. :')

[@lecturesbywalterlewin.they9259]

+Jonty Roy Thanks for reminding me. I had forgotten about that kid. I believe I gave this talk about 15 years ago.

[@jontyroy1723]

+Lectures by Walter Lewin. They will make you ♥ Physics. Wow! 15 years! Professor, do you have a rough idea about how many lectures you have given in your entire life till now? Just curious. :)

[@lecturesbywalterlewin.they9259]

+Jonty Roy I have given about 2000 lectures between 1966 and 2015.

[@jontyroy1723]

That is a lot of lectures! :) Thank you professor. BTW, your lectures from 2015, are they in this channel?

[@lecturesbywalterlewin.they9259]

+Jonty Roy My last lectures on this channel are my 8 lectures for Japan NHK TV (summer 2012).

[@sajidafridi6684]

Polarization and diffraction were one of my toughest topic of my life because we cannot done it in a practical way But from 2018 I start seeing lectures of Mr.WALTER LEWIN which can solve most of my confusion regarding physics I am from Pakistan 🇵🇰 Thank you Walter Lewin Sir

[@ajithchandran9643]

Your lectures are like, whole of my school science textbooks come back to life from coma. So nice, thank you sir!

[@jamescorrigan8056]

Professor Lewin reminds you what great teaching is all about. I managed to attain a M.Eng some years ago but never remember having had such an enthusiastic lecturer with such desire and energy. I did however learn one mnemonic for remembering the colours of the spectrum which for reasons unknown to me I still remember. Richard Of York Gave Battle In Vain :). Thank you Sir.

[@lecturesbywalterlewin.they9259]

Wow, thank you

[@neetachoudhary3980]

Sir you have occupied a large space of love in my heart. LOVE FROM INDIA🇮🇳.

[@lecturesbywalterlewin.they9259]

:)

[@jessesteinbar]

35:52 LOOK AT THAT, LOOK AT THAT! THE BEST TEACHER IN THE WORLD MAKING US LOVE PHYSICS! Thanks for this class, dear Walter! I love your teaching way!

[@aapddd]

Fantastische les professor. Ik was altijd al geïnteresseerd in natuurkunde maar nu helemaal. Uw lessen werken als een soort verslaving en ik heb er al veel van geleerd. Bedankt daarvoor !!

[@lecturesbywalterlewin.they9259]

Dit wordt dus een hele gezonde verslaving. Ik ben nu op vakantie in Nederland.

[@aapddd]

hele fijne vakantie gewenst, professor. ondanks het weer wat nu echt slecht is.

[@lecturesbywalterlewin.they9259]

we zijn in DenHaag het regent hier pijpenstelen.

[@minhokim8263]

The lecture is just amazing, it is an wonderful art. Beautiful!

[@sapradeep88]

Now I understand what they meant in Ray-Ban glass ad... Thank you sir.

[@morancium]

nice pun XD

[@Natashahoneypot]

Beautiful kids at the end seeing rainbows in sunsets everywhere they go. 🌈 💕 👶 🌸

[@g.lubins6144]

Hey Professor, I love your lectures. I noticed that around 19:00 you are commenting on the absurdity of the historic angle definition. But I think 360 should be given some credit for being the smallest number which is fully divisible by numbers 1-9 . Except for 7. Who needs 7 anyway, right? :)

[@carultch]

True that 360 degrees has its advantages, because of its divisibility by all single digit numbers except 7. It is very common to divide in half, thirds, quarters and eigths, therefore, a number divisible by all of these is preferable for that convenience. We'd need to pick 420 if we wanted divisibility by 7, but then it sacrifices divisibility by both 8 and 9. With dividing in 7ths, we expect exotic patterns of decimal repetition to appear anyway, so it isn't really a priority to plan for dividing in 7ths. You'd have to pick a number as high as 2520 to get divisibility by all numbers 1 thru 10. The historical reason why it is 360 degrees, is related to the fact that there are 365 days in a standard year. One degree is roughly how far the Earth travels around the sun in one day.

[@TIMxisxHERE]

there is something I don't fully understand here; Why exactly is it that the colors decompose when they go through the glass sphere? Is that caused by an attribute of light or by certain functionalities of our eyes and/or brain; As in, does the light ACTUALLY decompose into those colors or is it just our eyes and brain that make us see it that way? (I can also ask in Dutch if that helps ;) )

[@maxim25o2]

24:30 Wow, this experiment is so fantastic :)

[@jontyroy1723]

Professor, I have a query. Since our sky gets the blue color because of Rayleigh scattering, because of the tiny particles, can this be true that the sky we see now is more bluish than what it was thousands of years before? Since the pollution level has risen and there are more and more particles out in the sky?

[@lecturesbywalterlewin.they9259]

+Jonty Roy Good question. I do not know the answer. Rayleigh scattering only works for particles much smaller than 0.1 microns. I am not an expert on the composition (and sizes) of particles in pollution. All I do know that if the pollution is bad (like in LA) the air in the cities looks reddish.

[@sasmitadash9953]

Great... very nice explanation...loved to watch...many thanks Professor...best regards,

[@avinashbaldi3389]

Thank You Professor Walter Lewin. I'm watching your series of lectures of MIT and I feel I'm in another world-"The World of Physics". The way you teach and demonstrates I remember of ancient Indian "Guru" from whom we can ask questions and we became curious about the nature and universe. "Can I use old X-Ray sheet as polaroid sheets or not?"

[@lecturesbywalterlewin.they9259]

*what is an X-Ray sheet?*

[@JohnDoe-bw7bq]

Although I don't completely understand what the banana means, I have a rather good notion of what it is good for. I assure you Professor Lewin, that banana meringue pie is worth learning about, as well as ending it's existence completely, and I mean completely... furthermore, banana bread, bananas with strawberry sauce, banana flambe, banana pudding, banana split, banana cream pie, chocolate covered bananas, all of these things... I will fully and completely put out of existence upon the opportunity. I also firmly believe that whosoever seeking excellent ways will indeed follow the example which I have set forth on this day, and the fullness of intentions placed purposely within the parameters of the outermost desirable effect reasonably aquired during the period intended for the appreciation of the set direction toward achieving measures assuredly perceived to be right, good, and true, we all can collectively collaborate together with a fortitude of proper judgement as to what should be done...🍌

[@Protegit]

Im watching this video and doing all the experiments as you do, at the same time

[@lecturesbywalterlewin.they9259]

:)

[@fjs1111]

Banana on the shirt is so great!!

[@virgiliuantonescu247]

Excellent explained! Bravo!

[@rupashreekarmakar901]

You are absolutely fantastic! I am so inspired by the way you teach! Thank you for making Physics so colourful and interesting. 😍 P.S. Could you suggest another method instead of using cigarettes to show the scattering of blue light in a classroom?

[@SurajKumar-bs9zs]

Sir, I love your lectures

[@shayak2851]

Sir Why light passes through glasses but not through blackboards or rocks or that type of things ..???

[@marufhasan9831]

Sir I broke my laptop screen and took out the polarizer film for experiment. I noticed that any incoming light is going to be 100% polarized with just one film. One film is enough to block 100% of the light, 2 films are not needed. Why is that?

[@lecturesbywalterlewin.they9259]

I do not know

[@jessesteinbar]

47:34 so I'll not notice the polarisation of the light of a mirror (glass part) due to its metal back reflecting the same light wave? The metal will reflect a light that will confuse my eyes and I'll think that the polarisation didn't work well? Sorry, I don't understood it very well. Greetings from Florianopolis, from a Jewish Brazilian to the Great Professor Walter Lewin!

[@manipulativer]

hmmm. If you can steear polarized light with magnets, wouldnt the middle polarizer simply steear the light and "re-emit" by the known ratios?

[@lecturesbywalterlewin.they9259]

>>>>If you can steear polarized light with magnets,

[@manipulativer]

Could i get an explanation? "The Faraday effect is a phenomenon in which the polarization plane of an electromagnetic (light) wave is rotated in a material under a magnetic field applied parallel to the propagation direction of the lightwave." -google And the lens is a dielectric medium and the polarizing slits are of a different medium composition and could be interacting with light. Although i must add in the video i was supposing it would be 3 polarazing filters and the rotation of the middle one does not follow quantum mechanics but "re-emmision" of light @@lecturesbywalterlewin.they9259

[@Saraserenity28]

someone please help me find the exact spot where he talks about the beautiful sky and the particles and how we see the sight we see.

[@Protegit]

I swear Its the last vid before I sleep...

[@MEDSNMN]

Walter, you are truly one of the greatest teachers of physics in the world. I have learned so much from you and have watched many of your lectures and plan on watching each and every one of them. Why are the sun's rays 100% linearly polarized when hitting the earth?

[@lecturesbywalterlewin.they9259]

where did you get that crazy idea?

[@willnettles2051]

Was the green light the young person saw a modeling of the 'green flash'?

[@Protegit]

I dont know why, but when I put the 2 pieces of these polarizers perpendicular to each other and shine a white LED light through them it becomes blue (also its so much fainter but thats what I expcted. What I did not expect was for the light to change it's color).

[@lecturesbywalterlewin.they9259]

white light contains of all colors. Linear polarizers are not working equally well in all colors

[@Protegit]

I wonder why is that. How do they even work? Is there a lecture that explains the science of these plates?

[@sailorjerry3720]

Thank you for sharing

[@maxim25o2]

I am curious how looks polarized light in 3D drawings. Because explanation for polarized light described is now in only in 2D dimension drawings on paper.

[@lecturesbywalterlewin.they9259]

In linearly polarized light the oscillating E-field is only ONE 3D direction.

[@maxim25o2]

+Lectures by Walter Lewin. They will make you ♥ Physics. I try to imagine how that waves can look in water. when from spherical waves try to polarised them into stripes.

[@hseverins]

Hey Walter, ik wil je nogmaals bedanken! Je blijft mijn idool!!!! Maar om weer terug te keren, how in heavens name , ben je terecht gekomen in DWDD ? GroetjesHenny

[@lecturesbywalterlewin.they9259]

Ik werd uitgenodigd door Peter Eckhardt in 2011 - hij wist dat ik in Nederland was. We hebben elkaar kort daarna ontmoet in Den Haag and I accepted his invitation. Ik was 3 maak op DWDD

[@acershund1]

With this lecture he brings youth to Physics

[@muntee33]

Flabius Mabius Brang

[@ojosdeningshan1794]

Professor, I'm curious whether it's possible to change the light absorbance ability of a matter. For instance, why do things that are red only reflect red light and absorb lights of other frequencies? Is it because of the orbits of the electrons? that there isn't any orbit for the light of other energy state so the electron can't make the leap therefore can't produce that color of light?

[@lecturesbywalterlewin.they9259]

"The colour of materials is generally, but not always, determined by the chemical bonds in the material that make them up. Chemical bonds have specifi energies at which they can absorb light, usually transferring the energy to heat. So a red substance will have chemical bonds within it that absorb green and blue light, but whose resonant energy is sufficiently far from red that little of it is absorbed, and so is reflected into your eyes. An alternative form of colour is iridescent colour. In this case, it has a double layer on its surface, separated by a distance exactly quarter the wavelength of some frequencies of light. This means that those frequencies cancel out when the reflections from the two surfaces interfere, leaving other frequencies generally unaffected."

[@ojosdeningshan1794]

Thank you so much Professor, for your explanation!!! However, I don't really understand what do you mean by "absorb", I'm also quite surprised to learn that the colour of a matter is determined by the molecules of it rather than the atoms. What I previously was thinking was that the electrons inside an atom can only take certain wavelengths of light and leap into certain orbits, and each downward leap of from these orbits emit lights that it can reflect. It absorbs other colours of light because it doesn't have an orbit for those specific energy levels, so those light just go unaffected and 'unreflected'. But I see that my hypothesis gets really difficult to explain when it comes to molecules that have different kinds of atoms which have different electron orbits. Can you explain to me how am I wrong? Thanks! (I'm terribly sorry if this bothers you!)

[@lecturesbywalterlewin.they9259]

"absorbing" in general means that light is converted to heat (IR).

[@carultch]

​@@ojosdeningshan1794 The property of discrete spectrum lines for what a substance either absorbs or emits, is unique to gasses. That is where the quantum leaps between energy levels in the atom, govern the frequency of light characteristic to the element. The element when in its pure form in gas phase will either absorb these lines when it is "cold", or emit these lines if "hot", and will be transparent to everything else. With solids and liquids by contrast, the atoms are connected to one another through intermolecular forces. There is a much higher probability that the light energy's destination is shared between both an electron energy level transition, and thermal motion of neighboring atoms. This is why we can get a continuous black-body spectrum from a tungsten incandescent lamp, rather than a tungsten line spectrum. Whereas if you view a neon light with a spectroscope, you will see a neon line spectrum. Only the orange "neon lights" are actually neon. Other "neon lights" either have a different flavor of gas like Argon lights, or are actually fluorescent lights with colored phosphors on the glass interior.

[@meikejune4009]

I must look at your videos furtive. I saw the explanation, why light of rainbows is polarized.

[@waterboy8999]

I thought I was about to learn that bananas are a natural microphone.

[@terminate5888]

I think there is more to this. Light is electromagnetic because it has an electric and magnetic field which propagates at 90 degrees from each other. So for you demonstration the lights magnetic component is getting blocked in a liner polarizer whilst the electric field goes through in one situation. But this makes no sense. Light cannot simply be only electric or magnetic but only electromagnetic right? or can light be both or only one of them?.

[@lecturesbywalterlewin.they9259]

It's the E-field that generates a current in the rods parallel to E and that produces heat and thus the radiation does not get through. If E is perpendicular to the rods the radiation goes through.

[@terminate5888]

So does that mean that the M field gets through so that light is no longer electromagnetic but magnetic field when the E field is blocked? this cannot be the case,a compass isn't effected by linearly polymerized light. so the electromagnetic wave with the M and E field propagating at 90 degrees must get through.

[@lecturesbywalterlewin.they9259]

the entire radiation is absorbed when the E-field is absorbed. use google

[@terminate5888]

So if the E field is let through does the M field go through as well or is it blocked? Because from my observation it should go through so the light remained an EM radiation. Or is it that the models used to describe linear polarization simplified to get the idea across?

[@dishanktyagi4327]

@@terminate5888 you can understand it by displacement current in which a changing electric field between capacitor produces a magnetic field which deflects the compass

[@sujeetswarnkar1098]

Sir can electron be displaced if kept at rest in the path of polarized light??

[@lecturesbywalterlewin.they9259]

How electrons can be "trapped" is a lonf story connected to Nobel Prizes. I suggest you use google and find some articles

[@ibadurrahman6535]

love u sir from pakistan 🇵🇰 🇵🇰

[@schang8964]

What for is the banana? 😮

[@mobinaj9413]

Amazing 🤩

[@Sharmakanika14]

U teach in india or anywhere else?

[@GK-we4co]

If we take two pieces of glass, and put one of them in horizontal position and the other in vertical position, and we bounce light from the first piece of glass to the second and then from the second piece of glass to the screen, should we see no reflected light on the screen at all? Would they cancel each other out just like two polarizers put together at 90 degrees?

[@lecturesbywalterlewin.they9259]

I cover this in my lectures. It may be this one, I am not sure (i not find it) kzbin.info/www/bejne/gp-teo2VodyGeK8

[@GK-we4co]

Thank you!

[@troyertje1]

1:13:59 Professor Lewin dabbing before it was cool

[@anandthakur4616]

But I Mostly Love your Lectures Sir

[@Orangelina29]

And yet all the photos of the earth from sattelites doesn't have the "red light " edges!

[@pavankalyan-zi6ei]

Sir, it's so tough to imagine unpolarized light, could you help me in sorting it out?

[@lecturesbywalterlewin.they9259]

watch my 8.02 lecture on Polarization

[@carultch]

The simple idea of polarization, is whether the light wave's electric field is oscillating horizontally like a snake (call that "snaking"), or oscillating vertically like an ocean wave (call that "surfing"). Vertically polarized light has a surfing electric field and a snaking magnetic field. Horizontally polarized light has a snaking electric field and a surfing magnetic field. Unpolarized light is a mixture of both polarizations of light. Polarization is a property that transverse waves in general can have, but it is most commonly of interest to consider it for light and other EM waves.

[@bios546]

Problem #90? +1 like

[@UCSSamridhiParihar]

💓

[@paulcock8929]

No, in some sunsets one can see a green flash at the end of the sunset.

[@alimohebi9683]

That is due to eye retina recognition and has nothing to do with polarization

[@jerryhall5709]

If I try to pronounce Huygens in Dutch my vocal cords will drop out of my mouth.

[@ericpham7871]

Google already understand light and from sky to ocean is all open like our wife feel at home on a weekend easy dress

[@user-vj7qh2sc4f]

I still don't understand why light is overall separated when going through the glass triangle. Lets look at two light rays, one above the other. Each of them is being separated on its own, so isn't the higher frequency part of the above ray should combine with the lower frequency part of the lower ray, which will ruin the colour separation?

[@lecturesbywalterlewin.they9259]

how many minutes into the lecture?

[@user-vj7qh2sc4f]

At minute 52 the drawing of the triangle appears. The rays hit the upper portion of the triangle, bend and split. But what if you had drawn another ray that hits the lower portion of the triangle and its separated colours. Then its splinted colours would mix uncorrelatly with the upper ray's separated colours, which will ruin the overall colour pattern.

[@lecturesbywalterlewin.they9259]

Your question is not clear. You can draw any light ray (all coming from the same direction of the sun) and "march them through the water drop at different angles of incidence. Most will not contribute to the primary or the secondary bow. But some will. Ray tracing is not difficult. good luck.

[@muntee33]

Ahdriam Have a look at how tuning forks only make other tuning forks of the same note ring even though you only struck one tuning fork

[@Sharmakanika14]

Sir where u teach??

[@Scientist_Albert_Einstein]

Is no body going to talk about the banana gimmick on the pocket of his shirt?

[@jpnewshazaribagh8130]

Used to it

[@woodahkillah5583]

He’s got all types of different ones 🍳 🥯 🍌

[@confusedones02]

Sir can we describe ourselves as a wave???

[@lecturesbywalterlewin.they9259]

try it and tell me whether it works

[@confusedones02]

@@lecturesbywalterlewin.they9259 Sir we are made of atoms which may be assumed as a wave, so all the world may be assumed as a wave of different frequency....

[@confusedones02]

@@lecturesbywalterlewin.they9259 And Sir if we are waves then can we use superpositions??? I mean if we are also waves then we are in a large area so can I creat my own duplicates in the same time????

[@shayak2851]

@@confusedones02 And what if your wave collides with someone other's???

[@DavidLindes]

1:28:14 - awww, poor kid! Mixed up, "probably", but not in the self-deprecating way this person seemed to be thinking! :'(

[@schang8964]

In the 17th century, the word would be pronounced differently in Netherlandish 😅

[@muntee33]

That’s honesty... dont see it these days

[@maxim25o2]

If light looks like this - en.wikipedia.org/wiki/Computer-generated_holography#/media/File:PS_CGH.gif Then how will look polarised light?

[@lecturesbywalterlewin.they9259]

light does not look like that

[@maxim25o2]

+Lectures by Walter Lewin. They will make you ♥ Physics. No? I know that this what I show in link it's a interference wave. now I am watching another lecture about mystery of light, and double split experiment, and I come up with idea of light as many interference waves where pics of wave can looks like photons. I watch also another video about Einstein where he assume that light from sun is behaving like wave and also like a particle. and this is mind boggling. how particle can behave as wave? maybe with my thinking, light is a wave, and interference of many waves, create that pics, and this high points of water behave like particle of photon.?

[@maxim25o2]

+Lectures by Walter Lewin. They will make you ♥ Physics. anyway thank You for respond.

[@mariavalentine4827]

it was hard looking past the banana on his shirt

[@lecturesbywalterlewin.they9259]

:)

[@lit2021]

15:37 "It's cold outside, seek refuge" :D

[@kushalagarwal6706]

Why do you have a banana on your shirt

[@lecturesbywalterlewin.they9259]

just in case I got hungry during this lecture

[@curfimo9793]

@@eneasota wow didn't know that

[@pradeepsoni845]

🙂

[@dumbledor22]

Dear professor; i must state my opinion of criticism, that it is definitely totally morally wrong, to smoke dangerous drugs, even if it's for a scientific demonstration, cigarette smoke is dangerous. I understand that you must make some sacrifices for science, but don't you think there is a limit to this too? Besides what about the other people in the room? They don't have to sacrifice anything if they don't want to. And there might have been among them some who hated the idea of second hand smoke sacrifice for science, but felt to shy and awkward to walk out. Especially children, who might have felt awkward to wait outside alone from their parents, if their parents would even let them. Besides, couldn't you simply use some solid or liquid carbon dioxide, evaporating in room temperature? And even if you can do it only with cigarette smoke, rather don't do the demonstration at all, like i say: there is a limit to what you can and should sacrifice for science, even if it's only your sacrifice!

[@lecturesbywalterlewin.they9259]

😊

[@muntee33]

Lectures by Walter Lewin. They will make you ♥ Physics. My grandmother told me to say the same thing. I like the smiley face, nice touch.

[@neilonaniet]

Oh look ... someone else trying to ruin science with religious bullshit. Who decided it is "definitely totally morally wrong" to smoke anything?