I like how this channel pays attention to the comments, and tries to clarify things. I appreciate it!

this is the answer I have been searching for the past 15 years (since my 9th grade). Thank you very much.

Oh my God, finally i got the answer, i asked this question to my teachers, colleagues and family many a times about what actually happens at the atomic scale, they either ignore or explain those faulty explanations. Now i can die in peace Thanks you Dr Don Lincoln, 🙏🙏🙏 Love From India🇮🇳🇮🇳🇮🇳

Finally, this has been driving me crazy for years. Literally years.

I don't think I'm alone in saying that your videos //can't// be too long - I would happily watch you present a documentary. Thank you for your work, Doc!

I don't think this was a very long video. I'd love to see more 10+ minute videos on this channel that go into depth on a physics topic!

I was searching for this answer since i have developed my intrest in physics. i have searched a lot but was never able to find a proper answer. Thank you so much. i am satisfied now. I can now die in peace

Here a Graduate Physicist. There is also another simple explanation for this: (As consequence of the conservation of momentum of photons) If in medium 1 the index of refraction is n1 and in medium 2 the index of refraction is n2 and for the definition of index of refractions and wavelength we have: n1 = c / v1 , v1 = λ1 * f n2 = c / v2 , v2 = λ2 * f Dividing the above equations we obtain: n2 / n1 = λ1 /λ2 So if n2 is higher than n1, the wavelength in medium 2 is smaller than in medium 1. Now because the photon momentum is: p = h / λ Applying the conservation of momentum of the incident and transmitted photon along the parallel line of medium separation: p1 = p2 → h/λ1 *sin(θ1) = h/λ2 *sin(θ2) → n1 *sin(θ1) = n2 *sin(θ2) This is the Snell Law!! So the light bending is just a consequence of the conservation of momentum of photons!

This is my favorite channel for debunking every explanation I ever learned in my college physics classes.

As a high schooler, I've waited years for someone to explain the correct reason of why light bends. Thank you so much. 😭

I normally don't want to know the wrong answers.. but your style made it worthwhile...

Absolutely awesome explanation! The marching soldiers explanation always bothered me, and (regarding speed of light in matter) I could tell the scattering or absorption/emission explanations had to be false because the direction of light would change. It is incredibly refreshing to finally have straight answers to these fundamental questions! Thank you so much!!

Dear Fermilab. This second video does not really tell the story either. This is just another way of deriving Snell’s Law. The crucial point here is why only the normal component of the E field is affected by the permittivity. The “real” reason for the behaviour of light in a medium in this context is that light represents a force that in turn induces dipoles in the medium. This gives rise to a London force that always is attractive. Any component of the attraction other than the normal cancels out by an opposite force on the other side. Think of concentric circles on the surface around the focus that each result in an attraction. The larger the radius, each circle have more slanted induced dipoles. This is also the reason that the reflection results in polarization effects (Brewster). It is illustrative to imagine an object on a transverse wave. In an idealized setting the object will move only up and down - there is no sideways motion. Likewise, the London force resulting from the incident light will only affect the normal component (of the EM field in this case).

Nice when the presenter is also the thinker and loves the topic. This channel is our favorite, correcting many misconceptions and wrong / incomplete teachings. Dr. Lincoln clearly and succinctly explains.

These videos are really saving innumerable people from carrying on with the misconceptions....this way is totally so much effective to explain the misconceptions first and then the inconsistensies of them and then finally to explain the correct answers...a very few youtubers do so...i remember veritasium also said about the effectiveness of this method on the people...Thanks Dr.L

You have made a complicated phenomenon look simple, but I can understand the great effort behind it. Thank you Professor

this guy has the best ending line out of all science channels on youtube.

0:29 OMG my comment in a KZfaq video for the first time ever. I'm so happy for some reason. But Thank You so much +Fermilab for clearing up our confusion.

This is exactly how I wanted my questions to be answered. I appreciate it!

Sir , you are a LEGEND. This is the best explanation of refraction ever , in my graduation i learned this E perpendicular and E parallel but understood it today after 9 years, thanks for making such a video. Love from India🇮🇳🇮🇳🇮🇳

Methinks: "ha you obviously haven't heard of my analogy because it's simply fantas..." Dude: "number two, the marching soldiers anology" Methinks: "godamnit"

Stopped watching these videos for a while and now it has an epic intro... Nice

I really like these videos. The two that deal with light's speed in water and how it bends were very enlightening to me. I'd also like to see one on how light reflects from a surface at the same level as the other two.

Thank you for this explanation, I was taught the soldier reasoning ( 1966) at school and it never seemed plausible to me. I have no formal science education except high school science but I am an avid follower of all science ( subscribed to the New Scientist magazine for nearly 50 years ) and now subscribe to quite a few science based channels on the internet. This is a great time to be alive !!!!

I love this channel because when I asked this from my teacher she simply it said,"its a law' and never explained........

I love that you know and clearly identify the distinction between resultant description and physical causation, as well as the distinction between a mathematic description and its physical interpretation. It is too easy to stop at fermat's principle as the cause or to stop at the mathematical derivation and just say "the math says so." Very well done!

What I needed here was for the sound and sight of your explanation to slow way down when it entered my head so I could understand it.

This was my favorite subject when I was un undergrad! Calculating the resonance frequency of the electrons and seeing it in person was amazing.

It is surprising that even people who are into science communication on KZfaq end up teaching wrong stuff and we need channels like this to spread the truth. Please consider my request on making a video on The Principle of Least Action!

You said that "The only way to really answer the question as to why light bends is ... to embrace the fact it is made of oscillating EM fields..." And yet Richard Feynman, in 1984, clearly explained why light bends using photons as particles instead. In his book, "QED: The Strange Theory of Light and Matter" he wrote: *"I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I'm telling you the way it **does** behave - like particles." * Once he established that you were to think of light as particles, he covered wave-particle duality by showing how the probabilities of detecting a particle at a given spot mapped into waves thereby covering wave-particle duality. After reading Feynman's book, you can't help but think that glass acts as a giant Dalton Box scattering photons hither and yon but at the end, the most probable path a photon can take is through the glass.

Thanks a lot. I was looking for this concept and I am satisfied that the explanations you debunked(you also explained them well) clarified the problems I was having. I want to talk with you, Sir.

Great video. This channel is a real public service

I'm so glad to see fermilab explain this so acutely! It's all about the capacitance of the glass to store the electric field of the light, counteracting it, and finally returning the stored energy of the light upon it's exit.

Did you know that first explanation was the inspiration for the short story "Story of your life" which was made into the movie "Arrival?" It was somehow explained tot he author that light must somehow KNOW what the shortest path would be when going through a medium change. That meant that light had already seen the future. I guess it was really Variational principle in general, but the light thing caught him first.

I searched a lot for this question but no answer was satisfying me, but your explanation is amazing, I never ever even imagine that the knowledge of electromagnetism is behind the bending of light

What a spectacular video, the explanation, the graphics, the editing just perfect. If they taught science like this is schools, everyone would go for science

There are differing motives when explaining physics: 1. Describe what happens in a way people can remember WHAT happens. 2. Describe what happens in a way people can have a rudimentary understanding of WHY it happens. 3. Describe what happens in a way that only physics students can understand. I like that you took a middle ground between 2 and 3 in this video. Explaining physics to non-physics students is tricky business. :)

Absolutely Great, both the Explanation and the way it's explained. Thank you !!

I'm an RF engineer and this is one of the best electromagnetic videos that I've seen.

This video finally makes sense of Feynman's QED for me! I may have missed his explanation, but I never understood where the clock counting method came from.

Dr Lincoln, that video wasn't long at all. And thank you for the brilliant explanation! 👍

So many insightful comments. Glad to see so many people thinking

Never got this explanation ever before. Thank you sir.

Thamkyou for this video. I have taught this to my students every year for the last decade. I have found that if you use a car in method 2 , instead of a matching band it works much better, one wheel slips and slows as it moves onto the mud, the other wheel grips and pushes the car around.

I taught science & marked HSC physics over 34 years & although I have since retired from teaching; I learnt something that I didn't know. You are always learning & that is what makes life soooo inteesting!

Everytime when he says "Physics is Everything", that brings a smile on my face (being a student of physics maybe !)

Thank you! I love how you explain why the misconceptions are wrong.

I always loved to think about refraction in terms Fermat's principle of least time. Though I never really understood why would light obey this principle and know how to smartly change directions . Thank you for clearing things out

"Don't forget Uli's goodbye cake! 2:30pm" I don't know why that cracks me up. Dr. Don, you are freaking awesome!

About Maxwell's equations: "I let you the derivations because that's the fun part". Thanks !

Excellent presentation. Please keep enlightening us straightforward, with no bendings 😁😁!!!

This makes so much more sense and is so much simpler than any of those other "explanations" (none of which I'd heard before, although I never took a proper physics class; I did Chemistry in HS!)

Thanks for clearing up a misconception that was taught to me that I've been passing down to my students. Why doesn't the parallel component have to decrease, I missed that.

Thanks! Great video! Reminds me of what one of my professor told me long ago. Classical geometric optics is just Maxwell's equations + matching boundary conditions

I am really astonished as a physics teacher.Exellent explanation.i am highly satisfied.For the past 20 years I simply explained by mathematical expressions.Now prof explained with electric field concepts is seriously amazing

yes, finally a video that explains what is going on. I don't know maxwell's equations at my current level so I am glad you didn't just leave it at that and you actually took the time to explain what epsilon means physically.

Great video! I was always so damn unsure about those trivial explanations but this video explained very easily about that light phenomenon. Going through the wrong ones first made me remember about Dr. Richard Feynman and tomorrow is his birthday! 🎂🎉🎆

Q: Why does light bend when it enters glass? A: Because it is a pane in the glass.

I have been searching for this answer for the last 5 years ... Now I have finally got the perfect explanation 😍🥺

This might be my favorite physics channel! Awesome work!

Light bends because it is weak on the knees.

They never taught me this..glad to be here🤗

Exactly what I was looking for, Thank you! And the video is high quality, looks and sounds awesome

U are doing an amazing job sir!!!! Pls don’t stop making such informative videos

Very nice video. The example shown is for TM polarized light. Given that the boundary conditions are quite different for E and B, it'd be interesting to explain why we obtain the exactly same deviation for TE polarized light :)

I have derived those two results about perpendicular and parallel components in my electromagnetic field theory class but never thought it had so much connection with light bending...i wish my professors were like you to tell the real stuff and not making me derive these results for mere marks in exam.

Finally an explanation. Excellent video! Could you make one on how is it that we can stand above the ground and not simply pass through the atoms? I have heard about Pauli's exclusion principle but couldn't understand it well.

I am a new teacher covering the topic of refraction for the first time. ALL of my resources talk about the "Marching soldiers" theory. I thought I was going crazy. I ketp asking "But WHY?!" I really appreciate this explanation.

Thank you for the detailed explanation on the physical nature of what Epsilon means. I'm curious to know how the Tand Delta (or loss tangent) relates to this? Specifically I would like to know how does the energy in the field gets converted into heat within die glass. Thank you in advance.

Wow! I love how this channel approaches seemingly complex physics, with easy-to-understand explanations. The real mechanism for the bending of light is really interesting. But it creates several other questions: 1) As molecular rearrangements differ between different facets of a crystal, does this mean that different facets of crystals have different refractive indices due to different electric field environments? 2) Does this mechanism also explain total internal reflection? Or to be more precise, how does it explain total internal reflection?

You don't know what I feel. It's really awesome... Thank you so much for this explanation. Love from india

Very Good Video. I always enjoy your explanations. Oft times we don't understand the details (or the 'why's') of phenomena in the world that we have seen every day. Great Job!

And yeah, almost forgot. This wasn't a long video. I really like good explanations. A good explanation deserves ALL the time needed for that. I wouldn't mind longer videos in the future if it is required. I'm subscribing cause I love physics and this channel makes me love physics even more.

Best simple explanation based on true theory. You're great!

Wow! I''ve often wondered about this, and how it was connected to Maxwell's equations, which I've studied (but won't say I fully understood). Thanks so much for the fantastic and simple explanation.

Waaaaay above my head, but I think I understand now why when it is dark outside, and I turn the outside light on, that is attached to the house and very close to the glass door, the angle the light hits the glass is so close and that's why I see a reflection of the opposite side of the room when I'm looking out the glass. Thank you!

This answers one of my party killer questions i asked for almost 20 years. Thank you! Is there a video explaining reflection?

Fascinating! I saw this right after the episode on speed in different substances. So cool, and it was nice to learn Fermat’s explanation, too, getting it in context with wave interaction.

Thanks, you answered a question itching my brain since a long time :) I discovered your channel via PBS Space Time, I like it, you have a new fan ;)

Great explanation! I enjoyed that you went to Maxwell's equations instead of just saying induced electric fields change the speed in the material.

This video is not very long, it is long enough.

Great job, I love this channel, knowledge on the highest level that I can fully trust. I've been looking for an answer for this question after watching last video but nothing convinced me. Now I know why :) P.S. I also like your sense of humor, and I'm the person that prefers logical explanations than equations :P

This presentation is quite excellent. Thank you

Thank you for all these interesting videos. A really appreciate the effort and passion.

In the animation, the electric charges of the molecules in the glass moves/reorient themselves according to the direction of the light, but light travels through my window from many directions at the same time. So please explain how each light beam can bend when it transitions from air to glass, consistent with the equtions. One would think the charges of the molecules in the glass gets confused by the bombardment of light travelling through it from various directions? BTW, I love your videos - sooo much better that what you stumble upon on the web.

There's a readable explanation of the quantum kind in Feyman's QED book. This video gave the best classical explanation that I've seen.

I wasted a lot of time trying to understand explanations in undergraduate physics books. Often it just was too contrived. Thanks to channels like this, one gets real insights.

I've been contemplating this so much! Thank you! 😁

Thank you for the lovely explanation. I have a couple of questions for you and would be grateful for your thoughts: 1. Why doesn't the parallel component polarize the charge/substrate molecules? I mean what's happening physically that prevents that, not mathematically? 2. If I pump in external charge to a substrate using something like a Van de Graaff generator, would it change the permittivity and hence the ref. index of the substrate?

Perfect explanation!!! Thanks for this video. Maxwell equations give exactly the needed framework to explain most of the phenomena. These completed with the boundary equations and field conservation principles are a really elegant way to solve complex problems.

This channel is well above my pay grade but I enjoy trying to follow along anyway.

damn. This was so much needed. I had been searching for this answer. I almost had given up on this. Before this, I had an impression that it follows the marching soldier analogy with the fixed line, the only difference was I assumed that fixes line to be electric field but finally got the correct explanation.

Thank you for a beautiful explanation! I’ve always been confused by people applying Snell’s law to the incidence of refraction, often by using an ATV crossing into mud similar to the marching soldiers explanation. But I always wondered how that would work, as it implies photons have dimensionality that allow one part of it to cross the boundary before the other. One question: how come as the angle of incidence gets increasingly small you simply get reflection, as in fibre optic cable?

Ok, this is a good classical explanation, but let's go back to Fermat's principle for a moment. In particular I'm thinking of the explanation given in Feynman's little book "QED" (which I recommend to everyone's attention). Now it's true that Fermat's principle (i.e. of "least time"), as stated in the video, doesn't actually provide an "explanation". But when combined with the path-integral of the wave-function of the light Fermat's principle simply falls out of the physics. (Now, I want to clear that my respect for Dr Lincoln is absolute, and I'm perfectly willing to accept that I'm missing something here. But i'm not sure what that is.)

Ima go out on a limb and say this video is timeless. It will inform, teach, and enter people's minds year after year upon one man's discovery of the hidden gem in the the galaxy of social media. Forever is forever.

Great video. I'm no mathematician/physicist etc, I have been out of University since 98 (man, typing that, I realize how long it is lol) and was able to follow your descriptions easily. Every time I'd say " Ok, but what about..." U would start your next sentence with"ok your probably asking..." LMAO u answered in turn every thing I could think of it want to ask. Great job thanks and keep them coming.

I've learned this derivation at university and I remember that a key part in the derivation was that it is impossible for the electric and magnetic fields to exhibit discontinuities except for the case of a superconductor. Could you explain why the fields need to be continuous and why they are allowed discontinuities in superconductors?

Best explanation ever... Physical intuition+mathematical derivation. Thanks a lot!

I don't understand Physics but I am intrigued by it. You just made it understandable. Thank you!

I had the quest for it since long. Thanks a lot!