8.02x - Lect 29 - Snell's Law, Index of Refraction, Huygen's Principle, Illusion of Color

Snell's Law, Refraction, Total Reflection, Dispersion, Prisms, Huygen's Principle, The Illusion of Color, Weird Benham Top, Land's Famous Demo, Great Demos
Lecture Notes, Speed of EM Waves in Matter - Index of Refraction: freepdfhosting.com/c5f03c32d4.pdf
Lecture Notes, Color-Wavelength Chart: freepdfhosting.com/cd428dccf8.pdf
Assignments Lecture 29, 30 and 31: freepdfhosting.com/7d76b7e131.pdf
Solutions Lecture 29, 30 and 31: freepdfhosting.com/cc1c6d39d1.pdf

[@rao26jan1991]

Sir I have addiction..... It has been very difficult for me to sleep without watching your lectures for last many days.... 😊

[@lecturesbywalterlewin.they9259]

I am sorry for that - but the good news is that you will get very smart

[@rao26jan1991]

@@lecturesbywalterlewin.they9259 🙏🙏🙏

[@astar235]

@@lecturesbywalterlewin.they9259 Sir can you please do something good for Indian viewers. Can all these lectures be translated into an hindi audio voice?

[@ankitaaarya]

@@lecturesbywalterlewin.they9259 hahaha

[@akc21adt]

And this addiction is good for your mind but may be not for your health, if you are too addicted..

[@williamtaylor776]

This is the first time in my life I've heard a native Dutch speaker pronounce "Huygens." Thank you so much.

[@lecturesbywalterlewin.they9259]

This website contains all my 94 course lectures (8.01, 8.02 and 8.03) with improved resolution. They also include all my homework problem sets, my exams and the solutions. Also included are lecture notes and 143 short videos in which I discuss basic problems. ENJOY!

[@cheekymonkey3929]

wow, lucky students.😀😘

[@sameeradhikari3757]

i want all of them downloaded what should i do? finally love you and your lecture. unfortunately i will never get chance to meet you. i wish ................ may be in next life.

[@PradeepGupta-yj9nm]

Which website?

28:47 i'm stunned, how amazing this lectures are, this lectures make you see the world so differently

[@ths3100]

MIT students were so fortunate to have Prof Lewin as their teacher. What an awesome and brilliant teacher he is.

[@obayev]

Light is a complicated subject which is interesting to unfold with the help of such a great lectures. Thank you Professor!

[@lecturesbywalterlewin.they9259]

Glad it was helpful!

[@jameswilson8270]

Your lectures are always amazing!

[@lecturesbywalterlewin.they9259]

:)

[@sm-croia5427]

great lecture , professor. Your way of teaching physics through practical applications is truly commendable!

[@ruchirrawat8804]

hands down the best physics teacher the world has

[@nutankumari6674]

These lectures are timeless. Thank you so much sir.

[@archanababeley656]

Sir all these demonstration and excellent explanation for FREE . You are a legendary professor 🙏🙏🙏🙏. Hats off

[@lecturesbywalterlewin.they9259]

So nice of you

[@preetikasana9841]

Thank you , professor LEWIN . I was totally engaged IN THE LECTURE

[@stalemateraja]

Thanks sir your lectures are blessings for me i am 16 year old from india and i am going to use these physics principals to solve global problems your lectures are really amazing that i became better self Lots of love sir 😊❤️

[@sudiptaroy9725]

Thanks a lot Professor, these notes were extremely helpful.

[@lecturesbywalterlewin.they9259]

Glad to hear that

[@josiahwankhar4807]

Your lectures are the best and has helped me a lot. Thank you so much.

[@lecturesbywalterlewin.they9259]

You are welcome!

[@manasgupta6403]

Sir I am addiction to your channel Best physics teacher I have seen in my life

[@risegaming586]

You make me able to love physics I am very thankful to you Sir. Love from India 🇮🇳

[@forkids2642]

Prof Walter Lewin's lectures are very good, it can make you understand the concept in physics

[@KrishnaCalling]

Your are my favourite teacher...love from India Guruji

[@shivanshnigam8412]

Your lecture are amazing sir

[@andrcarb]

wow. Quite amazing lecture, one of the best of yours as far

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@thexcentric3655]

29:49 Explanation went straight to the ❤️

[@alistiqamat7066]

شكرا جزيلا الأخ ليون

[@fromexoplanet21]

Absolutely amazing lecture💖💐👏

[@lecturesbywalterlewin.they9259]

Glad you think so!

[@Abhishekdubeybusted]

Sir which sign conventions to follow : real as +ve or the cartesian one?

[@minhalrizvi587]

Best lecture of my life

[@ganesh3533]

Demonstrations are awesome sir perfect ❤️😍🙏

[@SciencewithRishit]

The top is so cooool ! Amazing

[@BobanVovan]

Thank you for this wonderful courses, Mr. Lewin! I can never truly express my entire gratitude for your efforts. I do however have a question. At around 25 minutes into this lecture, you mention that, in case the sound waves would behave as EM waves (lower frequencies have a lower refractive index, thus a higher velocity), the sound coming from a violin during a concert would come first, then would come the sound of a bass per se. Isn't it supposed to be the other way around, given that the violin has a higher sound frequency? (By the way, I became very excited when I found out that the university into which I've been accepted is the one you've graduated from :) )

[@lecturesbywalterlewin.they9259]

Liaten carefully to what I said: "if the high freq sound traveled faster than low freq as an example". In other words I did not make a direct connection with EM waves. What I said is fine.

[@multitude1337]

AMAZING ending, wow!

[@mohammedwaseemahmed2145]

Leaked the question for exam like a boss

[@asthamishra3148]

I come to see various experiments here ! It's really much interesting ❤

[@lecturesbywalterlewin.they9259]

Glad you enjoy it!

[@joelchocron]

Thanks for the eye opening lectures on physics - with all my humble opinion - i would be very glad to see - now that all physics basic university courses video are in place. A published book series of the "lecture on physics - by Walter Levin".

[@shivanshshrivastavavlogs3993]

IM A STUDENT OF CLASS 10TH CBSC ONCE MY SCIENCE TEACHER TOLD ME TO STUDY THINGS DEEPLY I THEN FOUND YOUR CHANNEL AND YOU ARE THE BEST TEACHER SIR LOVE FROM INDIA

[@pawejerzyna5674]

great lecture I really appreciate that :)

[@pragalbhawasthi1618]

I have a question regarding Newton's Explanation. 15:29 I think he could have argued as follows: Instead of the increase in vertical component of velocity, he could have said that there is a decrease in horizontal component of velocity. Then too, the ray would have bent towards the normal and the speed of light would have decreased as expected(keeping all else unchanged). Moreover, the reason for decrease in horizontal component could be possibly considered to be "friction", as water is denser(well, I don't think newton really distinguished optical density from matter density; correct me if I am wrong) So far, I think this explanation could have managed to survive for some time at least...

[@MrTHEcoolECOdude]

I just had a very brief question about the benham top. Why do would see the colors switching position when we reverse the direction of rotation? Isn't the rate at which a particular spot on the top the same whether we rotate it clockwise or counterclockwise and therefore we should see the same color regardless of direction?

[@lecturesbywalterlewin.they9259]

It's a good question. It has nothing to do with physics. Seeing colors is due to the way our brains are wired and the reversal of colors too. Try google

[@surendrakverma555]

Very good lecture Sir. Thanks 🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏

[@riteshbhartiya6155]

n = √(K*Km) K is dielectric constant, is Km relative permeability?

[@arafsartistry5421]

So the fact that when you pause the video or watch carefully, you can see the colours. I think that is because of the shutter speed of the camera. In a one frame (24fps of 30fps footage) duration ,the disk does not rotate a full revolution, that's why we see colours but a bit faded. If in one frame duration the disk could rotate a full revolution, then we might have seen pure white light. So my assumption is, if the footage was rolling at 30fps, then the disk have to rotate 30 rps(revolution per second) to be seen white to the KZbin viewers. Correct me if I am wrong sir.

[@robertroberts5627]

I don’t know how it’s done, but that sound of a dotted line when he is working with chalk is cool. If I wasn’t watching I’d swear it’s exactly the same sound the A-10 Warthog makes when it’s firing it’s 30 mm gun. Brrrraaaaa

[@adv.kirancharan6352]

I never thought optics could be that interesting 🤓

[@mnagarajan2010]

How does Cauchy's relation affect the formation of Auroras in the poles of the planet ?

[@MishkaKorobkov]

FYI was made experiments with measuring EM waves speed of different frequency and result very interesting, close to low frequency (few kHz) speed very low (significantly slower then speed of light) it will be very interesting to repeat this experiment and explain mechanism why this happens but that mean that speed of light is not constant at all (even red and violet waves must have significant and measurable difference of speed) and with waves of higher frequency it can be more than c

[@luciferwalker2910]

The day when I heard about you from Alakh Pandey sir I decided to study optics from you but now I have realised that my decision was not wrong

[@sools313]

these lectures should be translated to many languages

[@DebayanGhosh-ym8kl]

It will be more useful for Indian Students in Neet preparation because syllabus is more practical than theorytical

[@saptashwabaisya4202]

Sir, is there a playlist which contains all your lectures on ray optics?

[@guntassaran3667]

What's the secret behind eatable things(cup of coffee/tea sometimes banana) on Professor's shirt?????

[@srinivasub6149]

u didnt see wht he taught but seeing other than physics

[@sebastianrada4107]

I have been also thinking about it hahahaha What a mystery

[@samb55]

I'm confused about the relationship between the frequency of an electromagnetic wave and the index of refraction between air and water. At about 24:13, we see that lower frequency waves have a slower speed through a dielectric and a higher index of refraction than higher frequency waves. In particular, we see that waves with 10 to the 8th Hz frequency have a K of 78 in water and an n of 8.8. Visible light has a higher frequency (5 times 10 to the 14th) and a lower n, 1.33. Later, though, we learn that blue light has a higher n than red light. Blue light has a higher frequency than red light. How can blue light have a higher n than red light, and radio waves also have a higher n than red light? Seems inconsistent. What am I confusing?

[@lecturesbywalterlewin.they9259]

In the optical part of the spectrum the index of refraction (water and glass) are higher for blue light than fir red. Blue has a higher freq than red. Thus the speed of light in water is lower for blue light than for red light; this is some kind of an anomaly. Use google to see how speed of light varies at different frequencies. It's also discussed on Bekefi and Barrett which is the book I use for 8.03. Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8

[@kahoung9901]

same problem for me...

[@lecturesbywalterlewin.they9259]

that is correct. The speed of light will change, but NOT the frequency of the light.

[@BaldurKhr]

I had the same mind blowing question!! How can n(blue)>n(red)?? This implies that k(blue)>k(red)... but as we know the frequency of blue light is higher than red light so it should have been that n(blue)

[@poojyadav7442]

As a matter of fact, we can also tell that total internal refraction phenomena only take place when light enters from denser medium to rarer medium

[@pushpanjaykumar3985]

Sir should I use Rensik Halliday 'Walker' or 'Krane' for theory? PLS REPLY

[@mahjoubahmed9595]

Thank you very much prof l learn all the time from lectures I have suggestion you can explain quantum machines

[@prakashofficial3662]

Sir I am a commerce student but I watch your all vidoes .I am confused on myself why I am watching your vidoes. Thank you sir your a great lecturer

[@mrpotatohed4]

I'm glad nobody was around for me trying to say Huygen

[@sandeeppatidar1106]

Best lecture

[@trendingshorts4144]

Sir I try to download your lecture notes but your link is not working can you suggest me another way to download?

[@pritishekhawat9744]

Sir I have a partially silvered glass plate and a simple glass plate in my Michelson experiment. I just want to know how path difference in these two cases changes?

[@lecturesbywalterlewin.they9259]

ask google

[@musicbox6287]

Lectures by Walter Lewin. They will make you ♥ Physics. I didn't really understand the kappa and kappa of m. Isn't kappa used to described the permeability of the insulating material? How does it link to the refractive index?

[@lecturesbywalterlewin.they9259]

en.wikipedia.org/wiki/Refractive_index

[@stevenmai5235]

Hi professor Lewin, In your lecture, you said that if somebody increases the frequency, they will decrease the dielectric coefficient and therefore they will increase the speed. But then later you wrote down that blue light travels slower than red light in water, even though blue light has a higher frequency. Is this just an exception, or am I totally misunderstanding it? Thanks

[@lecturesbywalterlewin.they9259]

+Steven Mai Yes that is an exception.

[@parthkatke6706]

Best explanation I think is in the first topic of Lecture 12 of 8.03x by Walter Lewin

[@poojaubanshi8782]

Why do we have to take different ratio of the color in th disc it couldn't be like circular pizza 🍕 of equal ratio?

[@swaroopcool22]

I wanted to ask the following. When we turn on a torchlight we are producing electromagnetic waves. So are these a result of accelerating charges? Put differently is accelerating charges the only way to produce electromagnetic waves ? Or is there any other way to produce them ?

[@lecturesbywalterlewin.they9259]

It depends on the kind of flashlight. Google "incandescent" light, fluorescent light and LED

[@pritishekhawat9744]

Sir I have watched your videos on interference and diffraction but still I am not able to differentiate between these two and specially in case of slits.So can you please help me in understanding these concepts

[@lecturesbywalterlewin.they9259]

Single slit diffraction and double slit interference are BOTH interference and also BOTH diffraction. For historical reasons one is call "diffraction", the other "interference". But the bottom line is that the physics is the same ; it's due to Huygens wavelets that interfere with each other.

[@pritishekhawat9744]

Thanx Sir it will help me alot.

[@tehyonglip9203]

i did my best, i still cant pronounce Huygens, looks like you have to be a dutch to pronounce it properly

[@mwaqar2182]

Great sir

[@thebends6580]

Can someone please explain to me why when you look at a IOR table there's an index of refraction for materials like metal or stone or concrete? Light doesn't travel through stone... so wtf?

[@pritishekhawat9744]

If your notes can be available then nothing can be better than this.

[@lecturesbywalterlewin.they9259]

I posted on this channel my homework assignments + soln, my exams + soln and my Lecture Notes. You find them as pdf files below the video thumb nails.

[@MrTrickster273]

Hello Sir, I was a bit puzzled when I saw blue light with higher index of refraction than red. Blue has higher frequency, implying lower K (dielectric constant), shouldn't this mean lower index of refraction? Am I missing something? Thank you.

[@lecturesbywalterlewin.they9259]

Good question - it's called "anominal refraction" use google.

[@MrTrickster273]

@@lecturesbywalterlewin.they9259 Ah. I see. Thank you :)

[@stevenkaplan8471]

Can sin (theta 2) never equal 45 degrees? because x=0 (which can't be divided), what happens in nature?

[@vologaze7608]

48:14 Walter lewin: something bizarre is happening in ur brain me: is that a jojo reference?

[@ashishkumarpemmaraju2491]

Sir...as you said if all the VIBGYOR colors rotate at a high speed then due to persistence of vision it appears white.TRUE.But does that mean that something in the light bulb or any white source of light keeps rotating so that it appears white??

[@lecturesbywalterlewin.they9259]

no that's not the case google "blackbody radiation"

[@ronitdahiya7523]

Sir what is the maximum and minimum size of water molecule that can refract the sunlight

[@edwardroyaying9704]

Professor, do you have some thermodynamic stuffs on your lectures?

[@adityagupta2604]

It's in 8.01. Go see there

[@lollolzi2996]

How does ferrormaterials affect how light travel? Why do we have a kappa_m in the equation v=c/sqrtKK_m when light cant even travel through a solid?

[@lecturesbywalterlewin.they9259]

ferromagnetic materials have a negative index of refraction over a range of frequencies. It's a difficult topic. Use the web, use google www.researchgate.net/post/What_happens_to_the_speed_of_light_as_it_enters_through_the_metamaterial_wrt_that_of_vacuum

[@abdurrauf7525]

Respected Sir, could you please explain the reason for why light slows down on entering an optically dense medium. Also, does light refract when it enters from one medium to another perpendicular (parallel to the normal).

[@lecturesbywalterlewin.they9259]

the short answer is that the speed of light in a medium with index of refraction n is c/n. Thus it slows down in going from air to water. Why does light slow down when it enters matter? There are many ways to answer the question, and many ways to look at it, including “it just does - that’s the nature we have”. One easy way to actually answer it is to examine how Maxwell’s Equations, which interrelate space, time, electric fields, magnetic fields, charge, and how the two fields affect the matter in which they exist. The speed of light in vacuum, c, does not appear in Maxwell’s equations, but when you derive the electromagnetic wave equations by cleverly combining several of the field equations, something almost magical appears seemingly out of nowhere: a wave velocity equal to 1/Sqrt(µ0 ε0) where ε0 is the constant in Coulomb’s force law for electric fields from charges and µ0 is the corresponding constant for the magnetic force law - and this velocity 1/Sqrt(µ0 ε0) turns out to be exactly c! [In modern times the speed of light in vacuum isn’t measured experimentally anymore - it has been made a definition, and experiments are now done to measure the length of the meter based on the defined speed of light and the measured second, but historically what I said in the previous paragraph applied usefully at the time all this was done.] In matter, the electric and magnetic polarization of the matter by the fields requires replacing µ0 by µ and ε0 by ε, where is always the case that µ >= µ0 and ε >= ε0. These two measured properties of the matter describe how its polarization by the electric and magnetic fields weakens the strength of the electric and magnetic force laws inside the matter. Now here’s the important point, and the answer to your question: the speed of light in the matter now becomes 1/Sqrt(µ ε)

[@abdurrauf7525]

@@lecturesbywalterlewin.they9259 , Respected Sir, thank you so much. I will read it to make my concept clear.

[@shreejaltiwari4130]

What is the constant in u(mu) sin theta = constant and from where it is derived And thanks sir for these amazing lectures

[@tehyonglip9203]

sir i accept that c is 1/root (μ0ε0κκm) but in special relativity, there is a law that says that light should travel at the same speed for all observer, so who was right?

[@lecturesbywalterlewin.they9259]

Both are right. Any moving observer will measure the same values for μ0 and ε0.

[@KaviPriyan-qt6vc]

sir you told high frequency EM waves will tavel faster ..then how come blue light travels 1% slower sir?

[@lecturesbywalterlewin.they9259]

*that is an anomaly* as discussed in the 8.03 book that I used, Bekefi & Barrett. You can also try google

[@KaviPriyan-qt6vc]

@@lecturesbywalterlewin.they9259 thank you sir

[@mayankpandey5079]

Sir how refractive index of air is 1 is it imaginary or any calculation behind it?? Pls tell 🙏🏻

[@manishff4986]

From the experiment may be

[@debasishdutta9661]

Professor ,I asked you regarding the sign convention in lens makers formula. How is this possible

[@lecturesbywalterlewin.they9259]

question unclear - use google

[@MrBalthazar90]

If anyone has a problem with viewing colours with the spinning top, just try increasing the speed of the video. The 1.5 speed did wonders for me :)

[@mathssoso4261]

hi professor, if i want to understand Huygen's principle, what would you advise me?

[@lecturesbywalterlewin.they9259]

use google

[@manuferre7186]

Hi Sir, Do you know why the "triangle of the primary colours" is not exactly a TRIANGLE in your slides? I mean, they are curved! Has this any explanation? How do they affect the proportions when you try to find a colour rate by mixing them?

[@lecturesbywalterlewin.they9259]

use google

[@FF_BMG]

15:21 didn't get that sir. sine of an angle is the speed of that light ray? i mean V1/V2 ,and how can V1/V2 be the same as the sine of both angles? it confuses meeeeee

[@lecturesbywalterlewin.they9259]

google "Snell's Law"

[@FF_BMG]

sir, can you plz say what is the name of that box 37:19

[@boredscientist5756]

Well, if I may be picky, you don't have 100% total reflection. You forgot to mention the evanescent waves, but this is just a PCF specialist talking here. *ps:* a part about supercontinuum generation is clearly missing here (it is MIT after all....)! It was quite new when these lessons took place, it would have been super interesting to introduce them to it! Would have been amazing for them to be introduced to the marvel of optical fibers with a FULL lesson about it!

[@lecturesbywalterlewin.they9259]

en.wikipedia.org/wiki/Total_internal_reflection

[@dipender11]

sir is it always true for water or other medium of refractive index greater than 1 that if angle of incidence is 0 then angle of refraction must be 0 here incident light come from air medium

[@lecturesbywalterlewin.they9259]

If i=0 then r must be zero. sin i = n sin r

[@astitvagarg8997]

Hello sir , thanku for all the information you provide sir. My question is what is the explanation for energy dependence of a EM wave on frequency.. i.e. mathematically we know E =hf but how can this be explained in theory the reason for this dependence ? Why energy depends on frequency?

[@lecturesbywalterlewin.they9259]

EM radiation is waves as well as particles (in the case of light we call them photons with E=pc=hf). This is non-Newtonian and thus imcomprehensible we all think Newtonian. But that's the way the world ticks. I suggest as the time comes that you take a course in Einstein's theory of SR.

[@astitvagarg8997]

@@lecturesbywalterlewin.they9259 So sir this explanation can't be obtained from Newtonian physics about energy dependence on frequency?? Another question sir we relate colour associated to an EM wave with its wavelength but we also have a range of frequency associated to a colour of a EM wave ? But u said a physicist will ask the wavelength to tell u the colour. Can't this be done with the help of frequency also?

[@lecturesbywalterlewin.they9259]

@@astitvagarg8997 E=hf=pc De Broglie λ=h/p thus E=hc/λ the lower the wavelength, the higher the freq the higer the energy.

[@09gul]

Dear Dr Lewin, based on the dispersion inside the glass prism (at 27:15), why is it that even if the rectangular glass block (at 28:31) is very thick, we wouldn't see a red lining and a violet lining at the upper and lower edge of the emitted light from the rectangular block? If parallel light of different colours are sufficiently far apart, shouldn't we be able to distinguish the different colours?

[@lecturesbywalterlewin.they9259]

use ray tracing and you will get your answer.

[@09gul]

@@lecturesbywalterlewin.they9259 Dear sir, I traced a ray of white light, incident at 45 degrees through a rectangular body of water that is 20.3 cm thick. The separation between the parallel rays of red and violet light is about 1.7 mm upon exiting the rectangular body. Shouldn't this separation be visible to the naked eye? It doesn't seem to be so in reality.

[@lecturesbywalterlewin.they9259]

>>>>>If parallel light of different colours are sufficiently far apart, shouldn't we be able to distinguish the different colours?>>>> *yes, of course*

[@09gul]

@@lecturesbywalterlewin.they9259 that's not helpful. lol

[@MishkaKorobkov]

we have interesting paradox when saying the light is electromagnetic waves - it penetrating very deep (about 1000 meters) into salt water (it is good conductor) and this can`t be explained with Maxwell's equations, regarding his equations light should stops in the layer of few millimeters, how this can be explained? (author of this idea\question Atsukovsky Vladimir Akimovich, author of Etherodynamics)

[@lecturesbywalterlewin.they9259]

onlinelibrary.wiley.com/doi/10.4319/lo.1962.7.2.0207/full

[@MishkaKorobkov]

is it technically\physically possible to try an experiments to produce electromagnetic waves with wave size like a light the same way we making radio waves? (by real antenna like Hertz did) maybe using some sort of dividing original wave into short pieces? it will be very interesting to compare real light with such synthetic version (of real EM wave)

[@lecturesbywalterlewin.they9259]

laser

[@MishkaKorobkov]

Lectures by Walter Lewin. They will make you ♥ Physics. thanks, already think about lasers,light diodes and just simple lamps - seems need review mechanism to understand processes inside (not sure yet there something similar to Hertz experiment)

[@dipender11]

sir in case of concave lens when virtual object is right side of lens then why object distance is taken positive

[@lecturesbywalterlewin.they9259]

en.wikipedia.org/wiki/Lens_(optics)

[@prajnansharma3009]

Sir, lots of love and respect from Assam, India. I am a student of class XII. I have a question. If an object is moving with a speed v then its mass will also increase a little (though negligibly). Which will add up to a new kinetic energy. Since E=mc^2 therefore its mass will again increase and this process will continue. Is this depicting inertia of motion?

[@lecturesbywalterlewin.they9259]

if an object is moving with speed v, its mass wil not increase, but gamma will increase. E=gamma*m*c^2

[@prajnansharma3009]

@@lecturesbywalterlewin.they9259 Thanks for replying sir. But I don't know what gamma is. I will certainly try to learn these things. Thanks again sir.

[@akashaabeysundara8454]

Shouldn't that blue light be faster than red light because K for blue light is smaller than K for red light?(because velocity of EM wave is inversely proportional to the square root of K and if K is decreasing with increase in frequency, K(blue)

[@lecturesbywalterlewin.they9259]

speed of all EM waves (incuding light) in vacuum is c. in material with index of refraction n, the speed ic c/n. The difference in n for blue light vs red is an anomaly as discussed by Bekefi and Barrett.

[@akashaabeysundara8454]

@@lecturesbywalterlewin.they9259 Thanks a lot for replying, sir.

[@AliceKMay]

Good day, sir. I do enjoy your lectures and those help me a lot to visualise Physics with the reality. The thing is I have a problem. I do enjoy Physics and Physic classes, but I start to feel anxious whenever I have to solve the questions with mathematics, even though I practise maths properly. How can I improve it, sir? Thanks in advance!

[@lecturesbywalterlewin.they9259]

You have 2 options option 1: eat yogurt every day but *never on Fridays* option 2: Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam* You will find all information you need on this channel in three playlists "Homework, Exam, Solutions & Lecture Notes". 8.01 & 8.02 will each take about 200 hours, 8.03 about 250 hours.

[@AliceKMay]

@@lecturesbywalterlewin.they9259 Thank you so much for your reply, sir. I appreciate your efforts and kindness.

[@Kelvin-ed6ce]

@@lecturesbywalterlewin.they9259 I don't eat yogurt everyday.

[@suryak.pathak8741]

Hello Professor,how does refractive index of air varies with altitude?

[@lecturesbywalterlewin.they9259]

use google

[@debasishdutta9661]

Professor, we apply the sign convention in the derivation of lens makers formula yet we apply them in solving the problems. Won't both cancel​ each other.

[@lecturesbywalterlewin.they9259]

>>>Won't both cancel​ each other.>>> I hope not

[@debasishdutta9661]

But how

[@lecturesbywalterlewin.they9259]

use google

[@poojyadav7442]

37:34 the green light indicator more looks like blue in color why ?

[@canned_heat1444]

Hi, I thought the speed of light was a fixed constant that couldn't be changed, but in this lecture you say it's speed depends on the medium, was I wrong or did I misinterpret what you said?

[@lecturesbywalterlewin.they9259]

its fixed in vacuum c in media with index of refraction n it's c/n

[@canned_heat1444]

Ok, thanks.

[@DinosaursRule29]

Professor, could you please tell me what books were prescribed for this course? I would like to check them out. Thank you

[@lecturesbywalterlewin.they9259]

8.01 Physics Hans C. Ohanian 2nd edition W.W. Norton & Company ISBN 0-393-95748-9 8.02 Physics for Scientists & Engineers by Douglas C. Giancoli. Prentice Hall ISBN 0-13-021517-1 8.03 Vibrations and Waves by Anthony French CRC Press ISBN 9780748744473 8.03 Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8

[@DinosaursRule29]

Thank you, Sir! Your lectures are wonderful! My school teacher is (unfortunately) muddled up in her basics, so your videos have helped me a lot!

[@michaelknight2342]

@@lecturesbywalterlewin.they9259 thank you