Why does light slow down in glass?
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- Опубліковано 27 вер 2024
- Let's explore the age old question. Why does light slow down when it travels from vacuum to any other medium?
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I think 1 thing is missing here: the actual speed of light in the usual sense is not the phase velocity, but the group velocity at the front of the wave packet (which determines when the first part of the wave packet hits something). The light wave didn't exist for all time, but the 1st part of the light wave reach the electron at some time, and only after that the electron can also oscillate. So even in the case of x-rays, the group velocity would still be the vacuum speed of light, but the refraction is determined by the phase velocity, which is why x-rays are refracted away from the vertical.
ua-cam.com/video/KTzGBJPuJwM/v-deo.html
Thank you! I was just about to make a comment asking what the difference between "apparently" moving faster, and actually moving faster is, since he showed the front of the wave actually being pushed forward past the front of the wave in a vacuum, and that didn't make sense to me. Although he did make sense of some other things, this was the missing puzzle piece.
Has someone actually checked the group velocity of x rays in glass? I'm sure someone has, but I can't find it.
@@alexjohnward The Group velocity of light will slow down in glass and water. X rays and Visible light will slow down the same amount, but their Phase velocity and the angle of refraction will differ based on wavelength.
@@alexjohnward Nevermind, I've been reading more about Optics, and the Group velocity is dependent on wavelength. keep in mind that dispersion is talking about wave packets spreading out, like the envelope is getting broader and may be moving slower than the Phase velocity of the oscillating waves inside.
(Wikipedia, Dispersion) "If a light pulse is propagated through a material with positive group-velocity dispersion, then the shorter-wavelength components travel slower than the longer-wavelength components. The pulse therefore becomes positively chirped, or up-chirped, increasing in frequency with time" So an x ray should move slower than longer Wavelengths.
(RP-photonics, Zero Dispersion Wavelength) "Many materials have only one zero dispersion wavelength within the transparency region, with normal dispersion below that wavelength and anomalous dispersion for longer wavelengths. The group velocity then has its maximum at the zero dispersion wavelength. There, a light pulse travels with highest speed. For example, fused silica has its zero dispersion wavelength at 1.27 μm. For other optical glasses, far shorter values are common (often in the visible range), and more than one zero dispersion wavelength can occur."
Why is it always the channels with fewer subscribers that have the best explanations? You could not have explained this better!
Do they give Nobel prizes for youtube videos? Because you're blowing my mind over and over again...
That's one of the best videos on the internet! I really appreciate your work, because we don't have this kind of depth in high school's physics (speaking from Brazil here), so it's really great to understand it properly!
I am glad you love it. That’s the goal of this channel. To provide deep intuitive explanations! :)
After watching your video its my time to showoff my knowledge in physics to my friends....i am sure that i blown their minds exactly like what you did to me 🤯🚶🚶💯
Haha, great to hear that! Go Varsha go :D
Me too
Wow!!..blown away ...thankx mahesh...u r the best educator ever i seen on youtube...no one explained that way,they spoon feeded on this platform about light
My mind was blown when I read it as well. Appreciate the comment bro :)
After 3 years I finally got my answer, I have been asking this question to my teachers for ages but they just said ' THE LIGHT SLOWS DOWN 🤓' and if I asked why then some of them said ' LIGHT COLLIDES WITH GLASS'S ATOM AND LOSES SPEED 🤓 ' theni get frustrated and asked them WHAT ABOUT EINSTEIN, HE SAID THAT SPEED OF LIGHT (ie C ) IS CONSTANT IN ALL SITUATIONS , then they just ignored me.😅
Thanks Mahesh bhaiya
( Btw I'm still in school 😢 )
I like how you actually wave your hand when you get into the hand waving explanation.
Wow. I found your videos just recently. I have an engineering degree from a long time ago and I wanted to understand special relativity. I have some textbooks. I’ve watched a lot of different videos. Your videos are outstanding. Thank you so much!
I just wanted to take some time to point out how useful your videos have been not just to my to my knowledge of physics but also my perspective on learning. It is easy to believe a subject or topic is boring and not worthy of learning just because of who is presenting the material, without taking into account that everything can be made interesting with passion and love for something. Thank you @floatheadphysics and I hope you continue to make videos
This explanation and insight was great. Thank you.
Glad you liked it
I truly appreciate your content that you put on youtube,,,you are one of the best teacher delivering quality content,,,please do post more videos including dispersion of light ,i would love to have it...
Thank you
This is a brilliant explanation of something I had never even considered. It's almost 60 years ago since I was in college studying Microwave theory, which covered a lot of the same ground - wave phases adding or subtracting - but it was on a space commuications course (NASA), and we didn't go into optics. I knew from general interest how light refracts in glass, and I had always accepted on faith that it is because it slows down in media denser than free space, but the idea that it doesn't slow down - it just takes longer to traverse a glass block of fixed dimensions - is a relativistic thing - and Relativity is not intuitive. But I didn't know that X-rays refract away from the normal.
I can't say that it is all plain and clear to me now, but I can, at least, follow the argument. So refraction in glass, then, is dependent on the wavelength of the wave being refracted. I can't see if it would be directly proportional (I suspect not), but I'm sure there is a fairly simple mathematical expression that relates wavelength to angle of refraction.
I've just subscribed and become the 565th person to give it the old thumbs-up, and I'll be looking for your other videos. Clear explanations of scientific concepts are few and far apart! I've only seen this one video of yours, but I put you in the same bracket as Feinman - and, incidentally, Eintein, whose book "Relativity" (ISBN 0-517-02530-2) is also a brilliantly simple, non-mathematical explanation of a subject so complex that when he first proposed his ideas on Special Relativity, only a few other scientists of his day could come to grips with it.
I'd like to ask some questions, if anybody can answer them ...
1) Are there transparent materials other than glass where the natural frequency of their molecules can be determined (eg water, or perhaps dense gasses), that obey the same refraction formula, based on frequency of the incoming wave, and their own natural molecular frequency?
2) Has the time for light to traverse a block of glass been experimentally determined? Does it back up this lecture mathematically?
Hello sir, I got truly fascinated after reading your comment. Like how the majority of comments here are of Indian high schoolers [ 10th grade, which I am in also now] so this is my attempt to solve the questions you asked.
1. The thing is that glass since glass in it's latent form has excess electrons [ which can be recalled from the rubbing of silk and glass rod ] so in the video, he does not clearly show the happenings for the formation of another wave outside of the light wave because I think that it is very complex to understand that part so for the general audience it has been kept as unnecessary headache to teach.
But the thing about glass is that it is uniform, so the late phases happen uniformly which leads to rarer to denser refraction. But in the case of say water or dense gas, then yes the laws of refraction says that the incident ray and the refracted ray all lie in the same plane, so the refraction formula is already there in the form of snells law, or refractive index according to the speed of light in vacuum.
Those things are in my own school textbook so it will be easier to explain the formula in regards to snells law since our curriculum does check the basics and easy to understand concepts only for 10th grade level since we have social science, biology, mathematics(mainly geometry, introduction to trigonometry and statistics) which just covers almost everything basic of our high school. Then in grade 11th and 12th[ Indian system of classes] we have choices of medical or engineering in the science field, where in the pre engineering classes we will be taught calculus, advanced trigonometry and other things In mathematics, while in physics and chemistry it is thermodynamics, kinematics, optics, electricity, atomic physics and much more, and in chemistry we are taught about the atomic structure, many laws, physical chemistry, and organic and inorganic chemistry to prepare us for the college courses.
So to sum it all up, I still couldn't understand the topics very well that have been taught in this video, cuz physics and mathematics requires a hierarchical system of understanding, cuz without the basics, you can't understand the system presented by mathematics and physics. So I would like to learn all of this in detail later on in my higher studies but that is all I can answer for now
@@VictorKashyap-ie3zq Thanks very much for your considered answer. Most answers I get are two lines long, or simply "lol" or some other thought-provoking wisdom of the sort.
There is another video that shows the wave interference in a better way, I thought, but his conjecture is that light is, indeed, slowed down in glass. Still, if you have time, I think the wave illustrations are good, and show much the same information as in this video. ua-cam.com/video/CUjt36SD3h8/v-deo.html
I saw another video that claimed that light could be slowed down to 38MPH! Look up "How to slow light" I can't remember where I found it, but I don't think it was on UA-cam.
Something that occurred to me about *_this_* video is that at 2:52, he talks about light going through a thin piece of glass, and he talks about the phase change of the wave that causes the light to refract, and the explanation "hangs together" - except that it moves from that virtual thin piece of glass into the next virtual thin piece of glass, but if it bends as he says, you would expect it to bend in each virtual thin piece of glass, so that it would go through the glass body in a curve, eventually getting lost in a spiral. Well, we know that doesn't happen, and I'm sure the lecturer (FloatHeadPhysics) does too, but whatever happens only happens in the first virtual thin piece of glass, where the light enters from a different medium (air, usually). It is dependent on the _interface_ between air and glass - not on what happens in the glass itself. However, I do agree that if X-rays are refracted *_away from_* the normal, then some other explanation than the speed of light has to be sought. I have asked a question on the other video about that.
To be honest with you, though, I don't think I'm equipped to argue this case. I learned microwave theory and semiconductor theory (atomic structure of insulators and doping to produce semiconductors) a very long time back (I'll be 79 soon), and I've partly forgotten, and atomic theory has moved on a bit also. Now, for example, they are starting to doubt the structure of atoms - they aren't a nucleus with electrons flying around them any more - everything is *_fields._* I dunno - but then - I don't have to. In 5 years, I'll probably be gone - and I'm OK with that.
I wish you well for your continued studies. I'm sure you'll learn much more than I ever did. As in the song by Louis Armstrong ...
"I hear babies cry
I watch them grow
They'll learn much more
than I'll ever know
And I think to myself
What a wonderful world!"
Just a thought - could this phenomenon (refraction, and the bending ot the beam) be illustrated in any way with a compression wave like sound? It would be a lot easier to study, and to visualise.
@@DownhillAllTheWay hello sir, tommorow I have my mathematics exam, so tommorow when I will get time then I will do my studies on it, because my syllabus has already been completed, so getting the chance to answer and research these has been feeling great and improving the knowledge.
The song you had written has given me an awkward feeling, not of remorse or sad or happy or grateful. Just an unexplainable feeling of talking to a person who is not scared of his death, or that me being a young guy has not experienced life so for me I will welcome death but after when I fulfill my desired time of life, then I will not regret much, just like you
I love how u used topics that are familiar with everyone to describe this crazy phenomenon .Keep up the good work.
bro physics with you is art ! No video explained why light is delayed in a convincing way except this one, you made the difference by going into the details with is great, the details really make ALL THE DIFFERENCE, it's like to show someone how a home was built brick by brick instead of showing him how the home was built floor by floor, the brick by brick explanation method is the best and actually you are the only one I found explaining
why the light slows "brick by brick" ( with great details). Keep going like this bro you are doing awesome work, and know
that it's DETAILS that always make the difference in explanation ( explaining step by step without jumping steps). BTW I also think the same way as you with intuition, I found myself asking to me the same question you asked to yourself and you thanked the same way as I tried to do !
Your understanding of physics is in another level
From my school life i was curious and also tried to feel , understand what is happening and how.. Bt due to proper resources i can't think like how i want.. Then i shift from physic department to engineering bt i cant forget physics from my heart
However u r a genius person like me😁😁
Back when I looked at the phenomenon of light of different colors being diffracted as it entered mediums that were optically more or less dense , it always annoyed me that the textbook answer , more or less , was that the optical light is " slowed down " as it enters , say from air into glass . I was annoyed because I knew that light cannot " speed up ", or " slow down " in a medium - it must always have the speed c ( c= speed of light ) relative to the observer . Your explanation goes a long way toward clearing that up for me . And very interesting as well .
Best and fastest and most intuitive.explanation I've found on internet about the ligth transmission through a material. Before your explanation I had seen unclear explanations from some other well known physics youtubers, and I was a little clueless. Thanks for your clarity and simplicity. I really appreciate it, since it's not easy.....
I still don't understand how this resulting phase change of the light causes it to bend 🤔
Also, shouldn't the electric field of the electron also affect light behind it once it starts oscillating?
Is it possibly since light has only it's own phrase of rephrase through space. Always moving forward
Agreed! And the "energy conservation dictates phase change" description ignores the energy transferred to the electrons to get them oscillating kinetically in the first place. And if materials can be considered as being essentially a vacuum in this (glass) case, why not in all cases - why don't all non-metallic amorphous materials transmit visible light then? Mahesh is brilliant but this video raised more questions than it answered.
I'm with you. My *guess*: remember the light bend towards normal only happens when the light wave is at an angle to the glass -- if the light enters the glass perfectly perpendicular to the glass, it propagates through the glass with no angle change. The higher the angle of the light entering, the more the turn towards normal -- and I suspect the difference in the number of atoms on each side creates the imbalance that results in the angle change. If you consider the lightwave just a fraction of a moment after it enters the glass at an angle, there's just one glass atom above it that starts oscillating, whereas it's already got many atoms below it that are oscillating, which if you did the vector math, the imbalance between the induced waves of the one atom above and the zillions of atoms below, causes both the phase change and angle change. That's why light entering at a more oblique angle sees a greater bend towards normal, less oblique sees less change, and with a perfectly perpendicular beam feels perfectly symmetric induced waves on either side (so it gets a phase change but no angle change)
@joet9267 i do think one of the things that was missing from his explanation, in order to simplify it, was that he is only showing one propagating wave but in reality there would be lots and what we see is the probabilities of all them and all their interactions combined which is what causes the change in angle. I say this because otherwise you would not see the same phase shift when light entered perpendicular to the surface of the glass. so the phase shift and the angle traveled would have to have different causes if it happend at all angles. But as i write this i realize that still would not explain why x-rays bend the opposite as light waves based on the imbalance of oscillation idea joet9277's idea and i'm still not convinced i understand this whole phonominum. What am i still missing or misunderstanding? anyone have further thoughts?
also, even non transparent materials are mainly empty space so why do they reflex light instead of letting light pass through mostly unimpeded. I would suspect it's more about the field interactions, which are way bigger than the matter itself, and orientations of the molecules themselves. I would love further help to understand this whole topic. i have clearly missed something or there is still missing information.
I always had this doubt in my mind that why is it said that light slows down or sppeds up because according to the Special Theory of Relativity, the speed of light is a constant, irrespective of the medium it travels through and then I would think what happens during refraction. I even asked my teachers but didn't got an answer. But now I know the answer just because of you! I really thank you soo much for this video and all the other amazing video that you have uploaded (also on Khan Academy) I just had one question, why does the light bend? The light wave just got shifted backwards due to the resultant new wave but why does it bend away or towards the normal?
"the Special Theory of Relativity, the speed of light is a constant, irrespective of the medium it travels through" Einstein never said that and it is not in the Special Theory of Relativity.
I have struggled with these concepts for years . Thanks to your explanations, physics has now become so much more interesting, and easy to understand.
I have watched so many videos trying to understand quantum physics but believe me you are the best .
Keep up the good work.
Superb explanation ever
Boom! I know this feeling my brother!
It is the joy when you understand something so complicated. It is the beauty of Science!
Not sure that the X-ray wave is pushed forward, that would be the wave influencing the electron before it gets there. Tather, the X-ray wave is so small that the influencing wave is pulled back beyond the crest of the wave, resulting in the phase of the previous wave appearing in the next wave. (if that made sense)
@jimjohnson394 It is not that the Xray wave gets pushed forward. It gets pulled back so much that it is forward of the NEXT cycle.
Excellent good job !
I can't believe how good this explanation is. Amazing
Yep, fantastic.
Great And Great Explanation!! Great Work!! the besttt explanation! Specially without maths, Bestt!
Ohh Wow What a great explanation ever Thank U thank u thank u very much I am very very happy now. I am having a confusion on it ❤❤❤😁😁 keep going.. 🙌👍👍👍
Than you for this cool video. It blew my mind also as you showed that with the conservation of energy you can guess the position of the secondary wave. AMAZING :)
But here 2 additional informations:
1. As the electron moves up and down it emitts the Photon with a phase of 90° later according to the displacement. So the blue wave (secondary wave) is in the minimum 90° behind the yellow wave (primary wave) up to 270° behind the yellow wave.
2. Optics books never explain the situation, what is happening during the time as the first wave hits the glas. It always describes a steady-state situation: The light wave already passed through the glas, as we see it here in you explanation. So the claim of beeing faster then light ist mathematicaly correct, but the information actually already passed through the glas cause the whole glas is already filled with a light wave. So no information is moving faster then light. Never saw a mathematical explanation what is actually happening as the first wave hits the glas.
Interesting point of view. I'll need to think about it more, I'm not on board w/it, especially the xray theory but understand the thought. In my mind with xrays being much higher freq, the electron will only be 180 out of phase every so often, not for each wave. The video post; The Primer Fields Part 3 may interest you, maybe check out. The xray reaction has issues in the Primer Fields too. Excellent subject, look forward to having some extra time to think about it. Nice post. Look forward to reading the comments.
Ok sir, i get why light seems to slow in glass, but why does it actually bend? Like is it because it has to travel in longer time but with swme speed?
actually you are my best UA-camr
Perhaps this could be extended to explain why glass is good at reducing UV rays? Well done
I like the fact that you reply to all the comments. Btw your class 10th science video is helping me so much.😁
Awesome to hear that, Shail! :)
@@Mahesh_Shenoy oops! It's ‘Sahil’ not ‘Shail’ XD. I remember my friends used to write my name as ‘Shail’ instead of ‘Sahil’.
@@GodSahil that was autocorrect!!
@@Mahesh_Shenoy oh! XD. Np
God has graced you with a very intutive mind keep it up
Interesting. But how does this explain bending? And why metals reflect light so well?
You could have put diagonal electron waves in the picture to show how the lagging works or draw some kind of triangle to show the length difference. But that was the only part I had to skip to because I didn't understand it immediately. And the fact that I understood the rest what you said very well shows that nonetheless your explanation was really good. Great video👍
Great video 👍
Sir i think this was all about the speed of wave which you explained beautifully and someone has a good knowledge of interference can understand it easily but you did not explained why it bends? Or did I missed something 👀
No, I didn't explain why it bends. Wanted to do a follow up video which I never got to :D
I would be interested to hear if you have any similar explanation of the bending of light seen in gravitational lensing? Also why certain materials are transparent and others are opaque to light and why some reflect it.
21:07 can we just say that the electron in the mean position is in Direct influence of that electric field and the electrons above and below will get to the direct influence of electric field but after some tiny time delay.... 🤔
It is visible in the animation.... May be (mostly) i am wrong but it gives me a little more satisfaction 😅
Not really! Mainly because, and I forgot to mention that, we consider the EM waves from the source to be plane waves!
@@Mahesh_Shenoy i understand....
That's the main reason i said i am mostly wrong...
But we can perhaps say that the intensity of the electric field is more at the mean position than other positions which causes different acceleration to the electrons in different positions which may results in the case above in the video.... Probably 😁🙄
I literally studied only high school physics and currently in that phase preparing for JEE Which is in next 23 days..... And yes your channel helped me amazingly a lot in visualising the physics.
@@Mahesh_Shenoy or am i still wrong sir?
@@nothingspecial9370 plane waves have same intensity :D
Would wish you would use a pop-filter in front of your mic. The popping sound can become distracting especially listening with headphones. Very interesting videos. Love them.
The actual bending, not the slowing, is result of phase and vectors acting on the wave. Though the light can approach at one angle, the "shape" of it at any moment makes it more or less susceptible to being deflected. A tennis ball delivered to a single point from a single angle with different rates of spin. Replace the amplitude of the wave in the diagram with changing rates and direction of spin.
Superb way of explanation... wonderful
I love your video! Thank you for this work!
However, it opens new questions:
1) If the wavelength in glass becomes shorter then it should become shorter and shorter for thicker glass. And as far as I know, this is not what happens in reality. so, what is going on?
2) I was taught that photons deliver their energy to electrons only in packest of energies, shifting the electrons into different energy levels around the nuclide. So, how can the photos deliver just a bit amount of energy to the electrons?
Thanks again
2) You're mixing up two things. The quantization ("portions") of electron energy is a concept for the "orbit" the electron is in.
We don't change the orbit here, we just slightly "wiggle" the electron on it's orbit by it "feeling" the electromagnetic field that is the photon.
it need to get pulled back in every infinitisimal glas-strip, to continue the slower path. if it would stop to get pulled back it would go at c again
How the direction of light changes , is it due to phase change in medium
It's got to do with the wavelength shrinking!
@@Mahesh_Shenoy By shrinking you must mean changing. The direction of light changes due to any delta lambda, not just a shrinking one.
as an electronic engineer, I would call it retarded phase. In electronics, information can be transmititted by modulating the phase. I found this video very interesting.
Mahesh: You might be loosing me at this point.
Me: Mahesh, my friend, that's simply untrue.
Anyway great content, even though I thought I might end up blaming you for taking away time from my gaming session, I just can't at this point. Yeah, I'd be super interested to understand dispersion of light using this concept, would help solidify the concept itself too.
Aww! Glad you liked it!
Question: If visible light bends downward through a medium and X-rays bend upward, is there a frequency that can travel unaffected through the medium?
consider the analogy of exciting one tuning fork with another tuning fork of a different natural frequency. Energy conservation constraints will require the excited tuning fork to ring at the same frequency of the exciting fork, but somewhat "quadrature" in phase. Amplitude of the ringing of the excited tuning fork will depend on the difference between the natural frequencies of the two forks.
Small mistake here.
Electrons (or electron-shell) in phase is actually different. An electron (-) moves towards (+) the positive field. More electric field makes it move faster. This gives an additional growing negative field. Exactly in phase with the blue wave we see.
Electrons in phase of the light will absorb the light.
Electrons out of phase, too slow for the x-ray light, will not be able to follow the electric field. They will accelerate opposite. At the highest electric field, they are decelerating instead of accelerating. And this gives the second blue wave.
Optics can always be explained with waves.
I think there should be a good animation of what is going on. So many people don't understand this.
But maybe 3Brown1Blue will do that for the new "Barberpole" videos.
Fantastic video! Best explanation I've seen!
I'm still catching up and this is perfect
Super.... superbbbb brother. I gotta found your Chanel and watching almost all the videos up here.
So many misconceptions; such a tiny keyboard. But I'll try.
First, atoms are not mostly empty. They are full of electric field, distoted by the nucleus. When electons are bound within orbitals, they have density everywhere in the orbital. They interact with themselves from other circuits, which is what makes the orbitals. The orbitals are the shape of resinances in a 3-d drum, like dropping a grenade into a swimming pool. There's also time to consider.
Second, _c_ is not the speed of light. It is the conversion constant between time and space. It is like how airplane distance is measured horizontally in miles and vertically in feet. The number of feet in a mile is like _c._
Third, light doesn't have a trajectory. All those bendy lines are a mental abstraction. The only real events are when and where the light is emitted and when and where it is detected and destroyed. Everything else is up for grabs.
Light doesn't even have a speed in the same way this device would if I threw it against the wall. That would only have a speed because it's big. Even then, it would be an approximate abstraction. But light doesn't stick to itself, so it cannot be big in the same way. It interferes with itself and can cohere into a laser beam, and if you pretend it's a wave, you can talk about the wavelength, but that isn't the same as the bigness if this Anathema Device. See the uncertainty principle.
These are hard to understand, because brains only have meatware to understand thrown cell phones and waves, so we can do that quickly. The equations of QM and QED and QCD are pretty simple, but it takes years to understand and even then minutes or hours to work through, often more. This can take so long nobody has done quite a lot of it.
Fortunately, there's a trick that sometimes works: Feynman's Sum over Histories. You just imagine all the ways light can go, at any speed, even back in time, and you add them up or average them in a particular way, and you get the right answer, mostly and approximately. There are an infinitude of these, so it is daunting. Fortunately, most don't count enough to matter, and Feynman figured out how to get rid of the remaining infinities. As he said, there's always a little dirt or a little infinity. This is why he shared the Nobel prize with two others.
That probably doesn't help much, so let's try basic ideas. The idea of light going at _c_ in a straight line works for a vacuum because there's nothing in the way. (There's a little, but you can get rid of most by putting two plates close together so there's less room for stuff.)
If there's stuff, like glass, in the way, that reasoning doesn't work. If it's opaque, which just means that orbitals are so close together it's unlikely the light will have enough energy to go through, game's over. You might think it could go around, and you'd be right. But with a transparent material like glass, the light that gets through still has to deal with the stuff in the way somehow. The rest is math you could learn if you want to.
Just remember that all these words and concepts like speed and position and particles and waves are just mental tricks to think fast. None is entirely correct, and some are wildly wrong, but they work well enough much of the time.
thank you so much for great explanation
Great video, I like your presentation. Thanks for this explanation but there is one thing that I believe that you have missed out and that is that the incident beam of light/X-rays, must lose the same amount of energy as is emitted by the oscillating electrons, otherwise the resultant wave in the glass block would have to increase in amplitude no matter what phase the electric field generated by the oscillating electrons.
Then what happens when the incident beam exits the glass block, it must have a reduced amplitude electric field. Presumably the energy imparted to the electrons results in a reduced amplitude of the beam on exit from the glass block. and this is what causes the reduction in perceived light level the other side of a glass window,, for example.?
Your explanation of refraction has really got me thinking, I am sure that my school physics said that the speed of light slowed down in a glass block and therefore had to travel a shorter distance through the glass, i.e. got bent towards the normal.
This has really got me thinking about all of this, so thanks, but I would really appreciate your help on this.
Awesome intuition
Glad to hear that!!
the trouble seems to be that reality and models interact badly. the reason they say in vacuum is because when we see it we have to deal with observation. but in models we get to round off and ignore stuff. but light is not in vacuum, not even in space because space has stuff in it.
you seem to have forgotten that light is not just a wave but also acts as a particle. so we cant just make up stuff and pretend things like light is really alas in vacuum. because light does not go through a wall. if it were in vacuum it would go straight through a wall. but it doesn't. the model says it doesn't slow, it combines waves which changes the transmission then the wave goes back to fixed after leaving the prism. but it doesn't because the parts of light were changed differently depending on the wavelength. so we end up with a rainbow. so if nothing happened to the wave, why the spectrum? but we assume they then continue without a change in speed. have we measure the speed after accurately enough to find a difference in speed? no. but our assumption through the model says no. so light is slowed differently for each wave and the glass is heated, the light reflects, but we say it continues on because of energy conservation. not to mention the electromagnetic etc.
V= frequency * wave length
To keep the lights velocity same, according to your demonstration, wave length reduces or increases (depending on the place of generation of constructive waves?)
So i think when new waves length get shorter thn the frequency/oscillation should get increased and vice versa. But it does not support energy Conservation.
Hey! and what about the light emitted in the same plane but to the left? it should also be considered for the conservation of energy, right? btw excellent video. Very well explained!
Accurate interpretation, very nice. But how does this approach explain the refraction (bending)?
When passing light, does the temperature of the glass remain completely unchanged or does it heat up? If the glass shows an increase in temperature, wouldn't that indicate absorbation and dissaption of energy from the light source?
Thank you. I really like your explanations.
I think in this case the induced wave gets delayed so much that it appears in front of the next peak.
Anyway, could you explain how destructive interference works? You know, if you shine the laser light on an object, split it in two and delay one half by half period. Then the common understanding is that you will not see the light on the object. How is that possible from the conservation of energy point of view??
Why does light bend though ?
Even if light moves in a straight line , it can get delayed ( just like it is shown in your animations ).Then why does it bend ?
Really good question! Check out the video by Fermilab on this!
This explanation cannot be complete, because it conflates the crests of the wave with the wave itself, and because it doesn't explain why a change of direction would result, which would require crests of adjacent waves to be somehow bonded to each other. I think the handwavey stuff after the 19 minute mark must actually be crucial to understanding the phenomenon.
I've never found the Fermilab video "Why does light slow down in water?" satisfactory either, in part because it avoids the question of whether the combined wave is technically light or not. Both possible answers lead to contradictions with physics as I understand it.
I'm still looking for a truly satisfying explanation of how the existence of refractive indices can be reconciled with special relativity, for example what happens if you apply Einstein's thought experiment about catching up to a light beam, but inside a dense transparent medium.
That is very insightfull. So between visibile light and x-rays, is there a frequency where light goes through the material completely unchanged? As this will depend on the material in question, there would always be a frequency for which this material is perfectly invisibe, right?
fr bro? if so what is this frequency?? please lemme know
Make a video on Mechanism of florescence.
Amazing explanation ! 👌👌🌹
Thus, there must be a frequency of light in between visible frequencies and x-rays where the light does not refract ....
Hey, I have a question.
If the waves are Electric Fields .. then how come does they feel a pull or push , which a inertial
property.
I understand due the interferrence of the incoming light and the emission from electrons, the resultant wave has a phase difference. However, I am lost on how the resultant wave speeds up or slows down. I imagine phase lead (or lag) does not change the speed.
this was just perfect
So the electrons' wave lags almsot the whole period making it seem it's ahead of the photon's wave?
But then what happens to like the first part of the photon's wave? If the electrons' wave lags almost the full period isn't the very front unaffected? Also it's not like the photon gets faster, it still has to slow down or go without changing its speed, the "faster than light" comes only from the fact that it bends the other way because in a MODEL where it'd imply it's ftl.
I'll have to rewatch it to understand it better
Mahesh, I throughly enjoyed your other videos, especially about Maxwell's law and E=mC2 - great insight on the explanations! In this video, you made some big errors. First, you will not see the "bending" of refraction unless you are at an angle to the glass surface - perpendicular incidence, and you will not see this bending.
Second, apparently the velocity of light through glass and other media is lower than c in a vaccum. Light is not the same velocity in the glass, as you stated. Other comments have posted that and your comments in the video about that is wrong. Light apparently slows down in the transparent media - and I thought you had something very interesting, but on searching papers, light does slow down in other media, but how/why is the question you should have tried to answer in a video. I think you should to put a correction in your video - it is a glaring error. Own up to it please!
When the two waves coincide additively, it is the basis of a laser. Not completely by itself. It still needs added energy for that.
The speed of light in free space comes from the electric and magnetic properties of free space. Are these properties any different inside glass ? It would be strange if c, µ0 and ε0 were not in lockstep.
If the speed of visible light had slowed down going through glass , this would mean it could have a rest mass (as per your other video trying to understand E=Mc*c ) . So what does it mean by apparent speed of light if the speed of light remains constant at 'c' in any medium? If we are not measuring the actual speed of light when it travels through a medium what exactly are we measuring? You mentioned that atoms are 99.99999% vacuum so light will not be zig-zagging around , but then why doesn't it pass through opaque mediums?
From where does electron get energy to oscillate? If electron is getting energy from em wave ,doesn't it effect original wave?
This also causes problems with x-ray machines. Don't ever get a shard of glass inside you. The CT scan will not show the correct location.
Then, how do you explain regracive index as the ratio of the velocities
Thank you for the video. But I eas expecting intuition about approaching or going away from the normal. That part is not clear.
If the speed of light does not change, why is index of refraction (speed of light in a vacuum/speed of light in a medium) not always one?
so the exit wave from glass is forever changed from the input wave?
Sir , shouldn't the oscillating electrons produce electromagnetic waves propagating in both directions?
Great question! And that's reflection :)
@@Mahesh_Shenoy thanks😇
Why direction is changed in the above situation and another doubt is light incident on the water from the air medium at zero incident angle why direction is does not change ,explain sir
Have you considered that light may not actually be traveling at all? Therefore it has no speed to begin with. If light were a perturbation of a medium then what you are observing is an induced disturbance of that medium. The atoms, or electrons themselves could be a disturbance of the medium and don’t actually exist either. These atoms or electrons that matter is made up of are just disturbance of the medium and therefore there is no difference between matter and light, they are both just variations in the energy level and the type of motion of disturbance in the medium. The medium of course is the Aether.
6:25 why isn't the blue and yellow constructively interfering?
did you get it? after 9 months of commenting, or u still dunno?
9:15 there you go lol
god tier video
I know nothing but I was guessing in phase conservation would be yellow is reduced by blue amount since it would take energy to move the electrons.
That’s the only part I got lost on.
If the wave jumps forward for x-ray, is it possible to deliver information faster than light in this way?
Cool :)
When the light wave causes the electrons to oscillate, why will it not change? Don't we have already there "creation of energy"?
Great video!
Its amazing!.. But I hv an image to share my views..how can I do that?
Maybe you can share it somewhere and post the link?
docs.google.com/document/d/1zJqsNYVXAiRuky5DU9v8YTr47r8xS-MzUSLfKq7Nrak/edit?usp=sharing
Thanks :)
Sir it is said that a cell converts chemical energy into electrical energy. But I didn't get it that how this happens. Please describe the whole cell process.
Adding it to the list! Do check out galvanic cells
this theory could be tested and proved very easily. If you conduct the experiment but change the frequency of the incident wave, it should be possible to adjust the frequency to observe no refraction.
As far as i know, when light hits the glass, there is a momentum loss, which results with a phase shift, that we call refraction.. am i wrong?
If the way you tell is correct, the composite waves’ amplitude should have changed? Why didnt it? Or u just omitted the diff bc the electron generated one is so small in amplitude?
Besides fourier analysys can be of help.
The explanation is great for why light 'slows down' but to understand the bending you still have to use the analogy of a car driving through mud. I'm still confused as to why light *actually* bends when it slows down
Amazing!!!