@@stevenutter3614 I appreciate your comment that appreciated the prolonged thread of appreciation, as I realized how I assured the right spelling too :)
@youareonthetube1 Have I just seen a different video from yours? I did not hear the word "lie" in it. He does not talk about conspiracies here. All he is saying that some people in an effort to explain things to lay people (and themselves) are wrong or incomplete. Has your physics teacher when he talked about gravity explained curved space to you? I do not think so. In making things easier some people get too far with simplification and others have not understood the matter themselves that they are trying to explain. Science is about falsifying wrong hypotheses and explanations and that is exactly what this guy has done. Please tell me in what publications in scientific magazines you have spotted fraud and misinformation and proove to us what is wrong with it. Just saying that lies are getting spread without showing what and where is dishonest.
I still can't understand how this bending of light is any different from the gravitational lensing of light by massive objects (like black holes). That's due to gravity curving space time around it and light following the curved path. However, doesn't it hold true in this case too? May be glass being denser than air ( analogous to a galaxy being denser than vacuum), leads the space time around and with in the glass to bend a little bit (way smaller in magnitude though) and as a result we see the light through glass's denser gravity? (Similar to the Eddington's experiment to prove Einstein's theory of general relativity by seeing a star's apparent and not the real position in the sky due to its light bent by sun during a total eclipse. Similar to how we see the position of a coin placed at the bottom of a water jar to be slightly raised due to bent rays? And Einstein definitely used Maxwell's equations in his general relativity. So, couldn't this all be connected and we're understanding refraction wrong all this while? I don't know.
Vivek density and gravity are not the same thing; an extremely dense object will have identical gravitational force as a larger more diffuse object (as long as the mass/energy of the two objects is identical). One way to think of this is if the Earth is compressed to a size of roughly a 1cm diameter. Obviously it is extremely dense at this size, but it’s total mass/energy is the same. The space time curvature at the distance from 1cm Earth to the moon will be identical as the curvature from normal Earth to the moon despite the difference in density. Thus the moons path around 1cm earth will be identical to its current path around the Earth.
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!
Watch some of Leonard Susskind's lectures where he will give you a glimpse of how stuff really is if you have an appetite for more. You won't know how to do the math but you can follow his arguments as he goes through them and will come out spellbound.
Ditto! I'd honestly rather watch your videos than Neil deGrasse Tyson's or Leonard Susskind's! (Maybe because I'm more interested in quantum physics than astronomy, for the former, and because you work from scripts, for the latter.) Maybe not more than Sean Carroll, though. Oh, but if you could do a feature-length documentary _with_ Sean Carroll, that would be incredible!
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🇮🇳🇮🇳🇮🇳
Maybe mark deep dive videos similarly and only create them according to what interests viewers or creator. Keep the short ones as it keeps the channel alive and more input from viewers. Maybe a weekly deep dive to start?
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.
Yet, there is something wrong with his explanation! It simple don't work for TE polarized waves... So, he is replacing good explanations with a wrong one
He never said there was anything wrong with those principles, he only claimed and demonstrated why they are not the causal explanation of the phenomena.
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!!
@@alephii by TE do you mean transverse electric, any light with a transverse electric field? As in the electric field oscillates orthogonally to the direction of energy transfer? As in any monochromatic light in a homogeneous linear dielectric? I get you're trying to sound smart but you literally just tried to use the video's example as an example that wasn't explained by the video.
@@lachlanbunney6545 still, TE light also bends. The physics can't be different, I am not trying to be smart, just pointing out that if there is a flaw in the explanation then it is probably wrong!
@@lachlanbunney6545 By the way, a transverse electric field in TE doesn't mean that electric field oscillates orthogonal to the wave propagation, because that is obvious in the case you mentioned, but TE refers to the electric field transverse to the incidence plane, the plane that contains the incident and reflected light... The explanation is incomplete and probably wrong, would be much more precise to use the phase continuity in the interface...
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!
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
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!
34 years teaching science and marking hsc physics…and you never knew the answer to this question, nor in 34 years try to figure it out on your own in case someone asked?? What else don’t you know and never took the time to learn answers to basic questions?? YikeZzzzzzzz
Yes, I taught Science; geology, chemistry, biology & physics along with mathematics over the 34 years. You are obviously ignorant of a teachers work load to somehow think that you have time to find out & research every nuance of every subject that you teach. There was not a weekend that I was not marking assignments, tests or setting them. Apart from that also engaged in students welfare. Then you have a fool like you make the comment you make! @@AirborneAnt
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!
@@scottdc2105 "The conservation of energy only applies to anything with mass": Not true. Conservation of energy always applies . In the case of electromagnetic field (photons), conservation of energy is guaranteed by Poynting theorem: en.wikipedia.org/wiki/Poynting%27s_theorem Also note that my proof doesn't use conservation of energy but conservation of momentum. The conservation of momentum in electromagnetic field is guaranteed by the Maxwell stress tensor : en.wikipedia.org/wiki/Maxwell_stress_tensor
@@scottdc2105 A particle without mass can have energy and momentum. The classical formulas (p = m*v , E = 1/2 * m *v^2) are not valid for particles with speed near the speed or light or with the speed of light. Instead we need to use the quantum and relativistic formulas: p = h/λ , E^2 = (p*c)^2 + (m*c^2)^2
It is surprising that even people who are into science communication on RU-vid 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!
+Lakshya Goel You really arent going to get far in mathematics or physics if you keep asking why questions - the universe works the way it works, be glad it gave you a chance to experience it.
@@NinuRenee lol wtf! The whole point of science is to explain things, curiousity is what leads to discoveries. You are pretty much an animal in forest who doesn't know anything if you just say "it's the way it is, no fucking reasons for it to be" shut the fuck up if you can't understand things, don't demotivate people who actually want to find logic and explaination for physical phenomena....
@@affinix887 Maxwell's equations tell us "how" electricity and magnetism behave, they don't tell us "why" the equations are what they are. Science finds out and describes "how" nature works; it doesn't and cannot tell us "why".
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
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🇮🇳🇮🇳🇮🇳
0:29 OMG my comment in a RU-vid video for the first time ever. I'm so happy for some reason. But Thank You so much +Fermilab for clearing up our confusion.
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?
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. :)
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.
Because both initial components are actually derived from boundary conditions for M and E part. So this is only valid at entrance point. Further on, the wave propagates straight through that medium and both components are affected by the medium and as long as the medium remains the same, it behaves like perpendicular entrance to that same medium. Otherwise the light would curve in that medium which is not the case.
Apparently the ‘epsolom’ (sorry don’t know spelling) is bigger in glass than in air. This effects the perpendicular component. (I’m not sure myself why this doesn’t affect the parallel component too. Apparently it’s just the perpendicular component 🧐) Because of this, the angle of the perpendicular component is different to that of the parallel component. It is made shorter This creates the angle we see when light his glass.
He didn't explain it. 12:22 He showed E field entering perpendicular to the surface, thus the electrons in the glass lined up horizontally to cancel it, so he 'cleverly' deduced that the perpendicular E component got reduced in the glass. If E field entered at an inclination (which should be when light entered at any random angle), then by same logic, electrons in the glass should line up in appropriate direction to cancel it, so both parallel and perpendicular E field components should change.
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.
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.
What a hard question! I'm delighted that you have asked it. May I say it's all about the supremacy of geometry over physical mater. Any model that includes light waves or rays, and in particular the directions of these waves and rays is wrong by definition. Every such a model is by necessity a 3D structure displayed in an instantaneous space. It doesn't meter if these models were kinetically animated, they are still only the sequences of frozen 3D frames. BTW, the eternity could be the three dimensional only. To be able to answer your question one have to realize that there is no underlying reality of pictorial, i.e. geometrical, models and they should be looked at as if they were eternal objects themselves. However, there is no such thing as the 3D eternal model of light, or of electromagnetic extension in general. Light does have a peculiar direction which is always toward the observing, receipting, point. If you are interested in ... Respect
formolzinho a teacher once told me when I asked how long my paper should be his answer was that it should be like a skirt. Long enough to cover the subject yet short enough to still be interesting.
anyway I don't understand nothing because in genere physics today are made to don't understand nothing because instead to be something fun and relaxing is contrarity like a very long run of a deer in a forest. everything can be very clear if you want tolearn something but to learn something what is not so precious like a new form of energy bec ause this planet must clean herself from many forms of pollution. I heard light people don't knows what is it.
Methinks: "ha you obviously haven't heard of my analogy because it's simply fantas..." Dude: "number two, the marching soldiers anology" Methinks: "godamnit"
The one I remember being taught is the rolling barrel analogy. If you imagine a cylindrical barrel (more like an oil drum) rolling from pavement to grass at an angle, upon striking the grass first, one end will experience drag relative to the other and produce a torque similar to what Mr. Fermilab explained with the "rigid" lines of soldiers. It does replicate the geometry, but like Fermat's principle it provides no explanation as to why photons (which are often considered points or at least spherically symmetrical) would behave like rolling cylinders.
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 !!!!
after watch 2 videos, i think electric part of light is not enough to properly explain reflection think about it. reflection need parallel and perpendicular part of electric field to flipped 180 degree AND material generated electric field stronger after hit by light to make electric field flipped someone can correct me if im wrong or maybe have better explanation :D
I think reflection is explained by the fact that light is changing magnetic and electric field not just one or the other, the change in electric field gives rise to magentic and visa versa , in the reflection case it the electric field goes to zero as it is completely completely reflective material and hence the change in electric is negative which produces magetic field in the opposite direction which then induces electric field in opposite direction hence reverse the perpendicular component of the field while not affecting the parallel one and effectively reversing the direction of propagation in the perpendicular direction.
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.
Yeah, that has always been a problem for me. I'm fine with learning equations and seeing that it works, but I want to know how it works, otherwise I'm not understanding a god damn thing. 'The sun shines' is not an explanation as to why it emits light. Might as well say god diddit and here's an equation that can calculate the angle when it hits glass.
Talking about radio waves: These can be bent and change polarization in electric fields - think antenna theori. So that should also be possible with light? Is there any examples of bending light or changing polarity shining it between charged plates?
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?
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 think it's because the beam's vertical electric field is moving against the intrinsic electric field of the material, whereas the beam's horizontal electric field isn't. I'm only guessing though, and I'll defer to anyone who actually knows what they're talking about.
He did not show it. But said that we can get there after some calculus. The so called boundary conditions between two media are shown in em.geosci.xyz/content/maxwell1_fundamentals/interface_conditions/derivation.html It uses the Maxwell equations mentioned in the video, but in its integral form.
@@saspinski That's the math. It doesn't explain the physics. You would think the charges in the material would get polarized by the parallel component. The dielectric constant is also just an approximation, because it assumes the material is continuous.
To fully appreciate this result, you'd need to read the electromagnetic theory. The electromagnetic theory says that light is an electromagnetic wave, it is nothing but oscillating electric and magnetic fields. Electric fields and magnetic fields satisfy a set of 4 equations, 2 for electric fields and 2 for magnetic fields. The 4 equations are different for different media or materials. But at the boundary of two media, both equations of medium 1 and medium 2 must be satisfied, because the boundary belongs to both the media. So the electric field equations in one medium must be equal to the electric field equations in the second medium. This is what we call a boundary "constraint". The electric field is constrained to move in such a way that the boundary conditions or boundary constraints are satisfied. It turns out the boundary constraints you get on solving the equations is that the parallel component of the electric field must not change, and the perpendicular component must decrease. Please not that it is ok if you fully do not understand this, this is something that is taught in undergraduate physics course.
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?
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 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
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).
Hi, I found your comment the other day and it seems like the answer I'm looking for but I've been having a hard time getting at what exactly is happening. I think what you're saying is, look at an atom at the top "layer" of glass that's been polarized by the light and turned into a dipole. This dipole will polarize its neighbors. The neighbors on the same layer should apply a force to stretch that dipole out more in the transverse direction, but their forces cancel. The neighbors on the second layer stretch the dipole in the normal direction, and this force cannot be cancelled since there is no layer above the first. This almost seems to work out, but if the transverse forces cancel out and the dipole remains polarizes in the transverse direction, that component of the electric field would also decrease
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.)
Least action of path integrals is a real and important thing, but it's pretty non-intuitive for a 12 minute video, especially where a lot is debunking common explanations.
Still, the Fermat's principle on its own doesn't explain anything. Feynman's path integrals are really not a common knowledge that would be used in "dumbing down" the underlying causes for light bending on an interface. Being a _part_ of one of the possible solutions doesn't make the Fermat's principle a correct explanation.
@@Tomas.Malina : > Being a part of one of the possible solutions doesn't make > the Fermat's principle a correct explanation. Um.. of course it doesn't Which is precisely why I made this point in my comment.
I was wondering about TE waves in the video explanation... For TE waves there is no perpendicular electric field yet the wave still bend... Did I miss something or the explanation is incomplete and fails for different wave polarization?
You have to wait... someone is in the back room inventing long math equations. The show will start in fifteen minutes and you will be dazed and confused. A great show !!!
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.
This is the BEST explanation I've seen thus far!!! And I used to teach Physics for 20 odd years!!! And the fact that one can derive this result purely mathematically, using Maxwell's Equations, makes this a clear winner! This upload: *Why is light slower in glass? - Sixty Symbols* did a pretty good explanation using the idea of electromagnetic waves, but then it got bogged down with the chaotic and cumulative effects of the quantum electromagnetic nature of the wave's photons, interacting with the quantum electromagnetic effects of the atoms of the medium, as they too oscillate and produce such waves themselves as photons pass near them. Indeed, a new 'particle' to describe this phenomena: *the Polariton* was used in an effort to explain what might be happening in a quantum mechanical sense. I'm sure such effort have their merits, even though the maths involved must be INSANE so, this very simple approach in relative terms, using just the classical laws of Maxwell's Equations, for me makes this explanation the clear winner!!!
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.
@@joshuascholar3220 Yeah. The multiple solutions mentioned in this video actually *are* physically real, if they don't cancel out with other such solutions. If there's physical structure with details on the same order of magnitude of the wavelength of the light, you get diffraction grating, thanks to all those multiple solutions cancelling out differently. That's why optical disks are rainbow-y. Oily puddles get the same effect from how thin the oil layer is on top of the water. Man that's a good book. I need to read it again.
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.
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
It is because frequency of oscillating electric field is different for different colors, so you get different values of perpendicular and parallel oscillations, causing that slight change in direction for different colors (hence separating them)
I would just add that the plane of the exit surface of the prism is a factor. Leaving the glass through a surface angled from the entrance surface, the mix of photons that entered, exits on different vectors organized by frequency. With an exit plane parallel to entrance, like a windowpane, they take different angles through, but individually reverse by the same amount on exit, so they all end up back on the same path (as undifferentiated white light).
Because refractive index or the epsilon depends on the wavelength. For different color of light we have different epsilon so the extent of their bending will also be different. That's why they separate from each other!
After seeing your explanation many other videos also appeared in my feed telling the reason why light bends? Now I understand why it was more important to know the wrong explanations!😀 Thanks!!💐
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
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
At 12:05, shouldn't the charges move around in the opposite way? Positive must be downwards and negative upwards. BTW thank you so much, watching your videos really help me understand Physics better.
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.
YT should reveal the average duration and average number of times a video is viewed, backed up and o/w actively engaged. Thank you, FermiLab! Everything IS Physics!!
I had the same question raised in my mind and i read all three first explanations on various website and I too had the questions raised that its still not the complete explanation and this is the best explanation yet. But, as the final point depicts that the light's direction changed in glass as it had more densely packed electrons which resulted in an arrangement of electrons in the medium which created an electric field that opposed electric field of EM wave [light] which resulted in a reduced component of electric field of light. Since, for this explanation, electric field is developed in glass would make its one side [where light is incident] attractive to nearby negative charges and vice-versa on the other side [emergent]. If this were to be the true explanation of this phenomenon, it would also mean that if I turn light on/off very fast on single side of glass.....[light on] the charges will rearrange to oppose light's perpendicular component and and randomize when light is off. This means that charges were continuously accelerated and would hence develop magnetic fields due to light and glass will be magnetized. But since no such phenomenon has been observed, it means that this explanation is also so far not completely right. And if there is some mistake in my understanding of the concept that you explained please correct me and if not I would like critique response as well.
Lincoln's Huygens explanation misrepresents the theory. It's terrible, and it's because his wavelets originate only for each new wavefront impinging upon the interface. This is not Huygens idea though. Huygens ' wavelets originate at every point along the interface for each wavefront. The entire point is that all of Lincoln's extra wavefronts don't exist at all according to Huygens, because those are decoherent.
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.
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.
12:17 Isn't the arrangement of charges wrong? I mean if the glass particles were to generate an electric field in a direction opposite to the total electric field then the -ve ones must be above the +ve ones because only then we would get a field opposite to the total electric field.
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.
12:47 I assume the re-arrangement of the electrical charge takes some time. So what happens with the "first" photon hitting the glass. Is it going in a straight line because of the not re-arrangent electrical charge? Or is the re-arrangement itself already influencing that photon since the re-arrangment itself needs energy to happen? How can that influence happen over a distance if the light is going by c? Greetings
@@TheAbizgreat10 as far as i know that actual light, or that specific photon will be absorbed by the atom, but now the atom is excited meaning it has more energy wont be stable at that higher energy level, so it will re-emit the photon, but that is not physically the same photon but just the copied version of the original, so it looks like light comes trough glass, but its just the effect of it what comes trough. photon itself in theory moves in a circular shape, which has its own wave like motion, but when light comes trough glass its a different kinda wave, its more classical physics kinda wave effect, that one atom reemits a new photon, than that photon will travel with 300.000 km/s but only until its captured by the nearest atom, then again atom is excited but not stable, reemits photon again, so the light travels 300.000km/s all the time when its actually travelling, but absorbing and re emitting takes time, and that will make it look like that light is slower now, but its just a kinda trick this wave effect is now similar to the sound wave, where the sound is not actually gong trough stuff, its just the effect of it appears the other end of lets say the glass door, so u can hear a person talking to u and u can see them trough a glass door, but how the photon is actually moving in vacuum is a different story , probably no one knows how s that happening on its own, cause no one knows what the electromagnetic field is physically
Here he has treated light in a "classical" manner, like a wave. The whole "photon" (particle) interpretation and analysis does not apply in this case. To understand it in terms of the direction a photon is moving we would have to use quantum mechanics equations and principles like the uncertainty of position-momentum.
I got a low grade in HS physics (optics) because I argued that the textbook explanation was wrong. It was Snell's law based on Fermat's. I said that explains HOW but not WHY. How light "knows" how to calculate those angles. And the teacher got upset. The he tried the marching theory and I asked why the photons are tied together to bend. Why they don't just go straight, aligned with other photon. Didn't make it to interference explanation. I was ready to say that's good only for a LASER coherent light. In college I found out this explanation. Witch doesn't work either. If you send light between two electrostatic charged plates it does not bend based on the electric field.
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!
unless the glass has isotropic properties, also parallel electric field should induce charge orientation on the horizontal axis, thus the parallel field should be dumped by the inducted field... but this violates continuity of the electric field on the interface... so where am I 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
That was a great explanation. Now I would like to know, why some materials let light pass, some absorb light or some reflect light. What is the physics behind THAT?
Matter is made up of atoms, atoms have electrons in specific orbit(al)s around the nuclei, each orbit has a specific and fixed energy gap with other orbits. Suppose there are two orbits with energy gap of E, and you supply exactly E amount of energy to an electron in the lower orbit, it will take it and will jump into the higher orbit, if you don't give that specific energy E, little less or little more and the electron will not accept it! Now, lights come in different wavelengths and hence energies, some lights will have that exact amount E and that specific atom (of that matter) will accept it (absorb) and will get excited... you send light of slightly different energy and it will just pass through (refract). By the way, all that refract, they reflect too, in general, they scatter light....
@@atanunath Hi atanu, I am confused with the absorption thing. Is absorption always related to transition? I ran into some thing about absorption to x rays as a function of the x ray energy. It says the absorption decreases with the x ray energy gets higher until it reaches a specific energy under which the inner electron transition happens and abrupt increase in absorption occurs. I knew that absorption happens alongside the transition of electrons, but is all absorption linked to electron transition? What happens during the decreasing region I mentioned above. English is not my native language. Hopefully I pass my idea clearly.
Excellent explanation, my only pet peeve is when they say that light 'bends' in glass when in fact it's really redirected. To actually bend light would take an enormous amount of energy (greater than light itself) to bend.
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?
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.
Sir, thank you very much for this. Really appreciated. I could never figure out how energy is conserved in this experiment. Can you please explore that angle? Can this problem be solved using the conservation of energy somehow? Also, how can diffraction of light be understood with the help of maxwells equations? Which elements of Maxwells equations predict diffraction of light? Sir, can you please do a real in depth episode on Maxwells Equations? Thank you.
In the "Lazy-8" dipole photon model I"ve used for 40yrs in optical designs Brewster's Angle occurs when a photon "Centers Up" on media surface & leading half shrinks to size of a slower speed, but trailing half (still attached) just touches the glass surface and SPLITs off to be reflected away~ worked for me as I designed 1st LandSAT scanner IF U place a wood spatula vertical in a micorwave oven that has a wire grid suspended off oven floor U can get an image of a 2.41" half-wave "Lazy-8" photon w/2 concentric diameters> One dia of 2.41" and a smaller burn image of a photon that's absorbed by metal wire proportional to speed of electricity traveling along the wire> Simple to do but it tells U when a photon strikes a conductor, it "Centers Up" on the conductor as it transitions to its slower velocity