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.

@mikaelbiilmann6826

4 ай бұрын

kzread.info/dash/bejne/fYiuqaSDgNiwp7A.html

@Rationalific

4 ай бұрын

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.

Why is it always the channels with fewer subscribers that have the best explanations? You could not have explained this better!

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)

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!

@Mahesh_Shenoy

Жыл бұрын

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 🤯🚶🚶💯

@Mahesh_Shenoy

Жыл бұрын

Haha, great to hear that! Go Varsha go :D

I like how you actually wave your hand when you get into the hand waving explanation.

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?

I would say that the more intuitive way of thinking of the xray situation isn't that it pulls the wave forward, but rather it seems to because it delays it beyond a half wavelength so it appears to move the peak forward through a kind of wagon wheel effect

@Deuk

5 ай бұрын

To me this sounds more logical, otherwise we would be able to deliver information faster than light.😮

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!

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 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.

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

@Mahesh_Shenoy

Жыл бұрын

My mind was blown when I read it as well. Appreciate the comment bro :)

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

I love how u used topics that are familiar with everyone to describe this crazy phenomenon .Keep up the good work.

I suspect this is as good an understanding as possible without introducing the maths. Very well done.

I love how this topic has been covered by you, 3blue1brown, and Looking Glass Universe, and you each have different ways of approaching how to explain this complex phenomena. Thanks for doing this work and bringing such passion to every video!

Excellent work! Thank you!🌈

Thanks again for another great video. My 40 year old college degree is in EE, so I spent a lot of time thinking about sine wave addition. Your explanation made a lot of sense to me. Maybe those who don't have that background would think that one explanation is as good as the other. But without your explanation, I would have continued to be confused. None the less you did not address the change in angle, just the change in apparant speed of the light wave peaks. Would a spherical representation of the light leaving the electron help? I don't know. Thanks again for excellent clear videos!

You sir, are the utmost representative of intuition and simplicity, just like Feynman. I'm pretty sure if you were to be involved in research some 30 years later (teaching higher students), humanity would be thankful to your contributions! :)

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?

@rohanking12able

7 ай бұрын

Is it possibly since light has only it's own phrase of rephrase through space. Always moving forward

@dominicestebanrice7460

7 ай бұрын

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.

@joet9267

7 ай бұрын

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)

@Jeffhox

6 ай бұрын

@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?

@Jeffhox

6 ай бұрын

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.

Superb way of explanation... wonderful

Very good. The video from Fermilab got me halfway there but I was still unsatisfied because he didn't go into how the delay of the phase of the forced wave can vary depending on frequency. The x-ray thing too was surprising. I am now satisfied to the extent that I want - I don't feel like slogging through papers because I'm way too lazy for that! Thank you much!

@Mahesh_Shenoy

Жыл бұрын

Same here. I thought both the fermi lab and the science asylum videos were incomplete.

@craigtevis1241

Жыл бұрын

What about the Sixty Symbols video?

@craigtevis1241

Жыл бұрын

kzread.info/dash/bejne/dZ18sJKTh6ibks4.html

@lordofthemoodring

6 ай бұрын

@@craigtevis1241Ray Fleming has an interesting video worth checking out on this matter where he addresses what is wrong with the fermi lab video.

Do they give Nobel prizes for youtube videos? Because you're blowing my mind over and over again...

Boom! I know this feeling my brother! It is the joy when you understand something so complicated. It is the beauty of Science!

This explanation and insight was great. Thank you.

@Mahesh_Shenoy

Жыл бұрын

Glad you liked it

thank you so much for great explanation

Interesting. But how does this explain bending? And why metals reflect light so well?

I really liked your explanation.

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.

It makes sense how the light gets pulled back but why does it bend? You should something like light is going forward but an effect of coming back shows. Like when a wheel moves fast forward and it looks like its moving back or in a fan sometimes or a broken tv screen. Sorry it might be dumb question but wanted to learn more

Amazing!!!

Fantastic video! Best explanation I've seen!

Why does displacement take place though, lateral or longitudinal? That has always confused me.

There's a little problem in 16:40 time mark. It shows like the X-ray passing through the glass can reach the right side of the screen sooner than the X-ray passing through air. A more reasonable explanation is that the X-ray phase is delayed by more than a half wave per wavelength of propagation, creating an illusion that it was sped up less than a half wave. Hence, actually the X-ray propagates through glass even slower than ultraviolet light, which is slower than visible light.

@hamdaniyusuf_dani

Жыл бұрын

Let's say that the wavelength of the X-ray is 10 Angstrom, and the atomic spacing of the glass is 1 Angstrom. The phase of the X-ray is delayed by 7 Angstrom after penetrating the glass as far as 10 Angstrom. It creates an illusion that the phase is sped up by 30%. In average, each atomic layer of the glass delays the phase by 0.7 Angstrom.

@dozog

8 ай бұрын

I completely agree. Look how he gets there. (around @15:00) He says "there is another way energy can be conserved, that is if the blue wave is ahead of the yellow one" This is of course not physically possible. The effect cannot precede the cause.

@dozog

8 ай бұрын

I also don't think he uses energy conservation as an argument correctly. He first says the amplitude of the yellow wave remains constant because he assumes the glass has no absorption. And then uses energy conservation to argue the blue wave cannot be pi or 2pi phase delayed. Where does the blue wave gets its energy from?

Bro I love watching your videos. Please continue making more!

Thanks a lot for this explanation ❤

Very nice and complete explanation

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👍

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?

@ricomajestic

7 ай бұрын

"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.

Amazing 😍

I have a question about 10:12 where you say that it violates coservation of energy because energy is destroyed are we sure some of the energy dosent just transfer into momentum for the electron? Because if its shaking up and down once the photon hits it once it past wouldnt it just keep going after once the last peak stops interacting? the way i see it the osscilating fields cancel out this momentum allowing the electron to basically be trapped in the photon but one it leaves wouldnt it leave an impression in the momentum sense there will be a poin where the ossciallation stops? wouldnt this allow for a photon with weaker magnitude?

Super.... superbbbb brother. I gotta found your Chanel and watching almost all the videos up here.

I can't believe how good this explanation is. Amazing

Amazing explanation ! 👌👌🌹

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.. 🙌👍👍👍

Great And Great Explanation!! Great Work!! the besttt explanation! Specially without maths, Bestt!

Thank you for the wonderful explanation. Does the wavelength of visible light actually shrink in the glass ? Because this then would increase the frequency and create energy right?

@Mahesh_Shenoy

Жыл бұрын

Well, the perceived speed changes keeping the frequency unchanged. Thanks :)

Hi. Could you share some of the resources /reading material you used while researching this topic. Thanks. The video is insightful.

@Mahesh_Shenoy

Жыл бұрын

Check out Feynman lectures!

God has graced you with a very intutive mind keep it up

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 👀

@Mahesh_Shenoy

Жыл бұрын

No, I didn't explain why it bends. Wanted to do a follow up video which I never got to :D

@alexlewin9997

Жыл бұрын

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.

At 14'07, I don't understand but it seems that there is more periods in the signal travelling in the medium, like if the frequency have increased (it looks like phase modulation in signal transmission), is that possible ? Why can we explain the change of direction that does not appear in the figure ? Thanks for all :)

Why am i getting goosebumps whenever sir says boom! in this video 😂

@Mahesh_Shenoy

Жыл бұрын

Yea, why? :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.

You never actually talked about refraction. We can see that "slowed" visible bends toward the normal effectively shortening it's path in the medium (which I assume exactly compensates for the "slowdown". While the "speed-up" X-ray bends away from the normal effectively increasing the length of its path, again cancelling the effect of the "speed-up" So that the transit time across the thickness of the medium is that same as if the medium wasn't there in both cases. Right?

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?

Perhaps this could be extended to explain why glass is good at reducing UV rays? Well done

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

@whuzzzup

4 ай бұрын

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.

@dovahkiin2

Ай бұрын

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

Excellent video, from far the best one I found about the subject thank you really much, but please bro I still have a very small question, at 12:00 when we look at the green beam as you said it is behind the yellow one (its peak), but how can we interpret the small piece of green beam that is ahead of the green peak ( at the extreme right of the screen), what is it ? because when the yellow peak will reach the receptor the green peak won't reach the receptor but instead of the peak it will be this small piece at the extreme right, so do the yellow and the green beam arrive at the same time but in a different phase (like yellow will arrive at its maximum and green at its minimum) ? Please bro I have been searching for 2 hours but I didn't find...

@rfvtgbzhn

7 ай бұрын

Yes, he refers only to the phase, actually the blue beam is generated by the electron, so the electron starts to oscillate with a bit of delay and at the beginning the green beam is just the same as the yellow one and only after some time the electron will oscillate fully and the green beam will look like in the video. Also in reality the wave of the light itself will not start at full amplitude, making it even more complicated. But in general the start of the whole wave packet (which is what is usually meant by the speed of light) should be determined by the start of the yellow beam, so it can't be faster than the vacuum speed of light. But I still don't understand how it can be slower. PS: I just found out that the start of the whole wave packet (= the start of the green beam) actually also can't he slower, it is always exactly at the vacuum speed of light. en.wikipedia.org/wiki/Front_velocity

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.

My own, admittedly, imperfect analogy is to think of crossing a chasm on a bridge made of swinging boards. The boards' swing frequency can not be changed and the runner's step frequency can't either. However, long legged runners swing their legs slowly and short legged runners swing their legs fast. So all runners have the same speed (lambda times f = c). A runner who swings his legs slowly may find himself hitting the boards when they are going back and so is always delayed. A fast swinging runner may hit the boards when they are swinging forward and, thus, crosses the chasm faster. It all depends on matching the leg swing frequency to the board swing frequency. If a runner's leg swing just matches the board swings he may end up not feeling the boards at all and his timeing to cross the bridge would be the same as with non-swinging boards (refractivity index of that bridge would be 1 for his frequency). If the board swings are just as fast as the leg swings, the runner may end up going nowhere and it could be said that he has been absorbed; as in red light not passing through blue glass. There's a reason why swings are always used to explain resonance frequency.

actually you are my best KZreadr

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?

@pleasejustlmb

6 ай бұрын

fr bro? if so what is this frequency?? please lemme know

Great video!

Great explanation thank you! To clarify, the light still reaches destination at time d/c right? As in I can’t cheat and a laser going through a glass rod wouldn’t actually win a race with a laser in vacuum - information can’t get to me in under or over d/c if I’m looking at the source through a glass rod.

So the phase shift of the induced wave depends on the light's frequency relative to medium's resonant frequency?

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 !

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.

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!

Well explained....in terms of wave but how about photon, particle perspective ????

When passing light, does the temperature of the glass remained 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?

Accurate interpretation, very nice. But how does this approach explain the refraction (bending)?

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.... 🤔

@nothingspecial9370

Жыл бұрын

It is visible in the animation.... May be (mostly) i am wrong but it gives me a little more satisfaction 😅

@Mahesh_Shenoy

Жыл бұрын

Not really! Mainly because, and I forgot to mention that, we consider the EM waves from the source to be plane waves!

@nothingspecial9370

Жыл бұрын

@@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.

@nothingspecial9370

Жыл бұрын

@@Mahesh_Shenoy or am i still wrong sir?

@Mahesh_Shenoy

Жыл бұрын

@@nothingspecial9370 plane waves have same intensity :D

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??

But if we use Maxwell's equation for light speed c= 1/√μ€ , which comes out to be different for different medium , Are they wrong ? Or do they include this effect and then tell the apparent velocity .

@Mahesh_Shenoy

Жыл бұрын

The later one. The ‘apparent’ velocity

Your explanation in general is correct and I congratulate you being one of the few giving the correct explanation but IMO not entirely. The laser visible light wavelength is too large to make the electrons inside the atoms (glass is a dielectric it has no free electrons) in the glass to oscillate similar to the photoelectric effect) . It is not a dynamic EM wave interference effect but simply the quantum electrostatic scalar matter field of the glass material compresses the wavelength of the light inside the glass. In the case now of the X-Rays there indeed we have oscillation of the glass electrons and light waves interference effect that changes the phase velocity (not group velocity c) of light inside glass which becomes effectively faster that c value (refraction index n

Excellent video, although I have a question, what happens with the waves "we see"? I mean, to measure anything, there must be light that comes out of the thing being measured, and approaches the thing that measures. For example, how do we know that the light is not doing something else, and it's the light that goes towards the measurement apparatus (e.g., our eyes) what "implements" the effect?

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.

14:10 - if the wavelength shrinks, the frequency increases, so each photon has more energy. This looks like it violates energy conservation, no? Unless the light intensity there is less than before and these two effects balance out? Is this what the explanation is here? 16:28 - also with xrays, this would imply causal action can now travel between events between which it couldnt without the help of xrays+glass. How do we solve this paradox? My explanation was that the very first part of the wave travels as if no interference happens, and the "speed up effect" only happens to the parts of the wave that follow. Because the electron's EM wave isnt actually ahead (in phase) of the incident wave, but is so far behind that it looks like its ahead. This would mean the very tip of the incident wave remains unaffected? No clue if this is right so please correct me The reason i said the electron EM wave cannot actually be ahead of the incident is because electrons take some time to accelerate once the electric potential at their position is changed by the incident wave. 23:04 - if the further-away electrons are not in the right positions wouldn't that mean that the blue wave isnt in the exact correct phase difference to the incident wave, hence there wont be equal amounts of constrictive and destructive interference. This suggests that things like the density of the glass (or any property that affects the arrangement of electrons) messes with energy conservation. Apparently the quantum version of this model is more precise in the details but i havent looked at it and i probably won't understand it. Just one last thing - Ive heard people say the group velocity is lower in glass but the phase velocity is constant. Is this true? If the light isnt actually slowing down (or speeding up), but the pattern of the wave is pushed back, then information should still flow slower. Imagine an experiment with a detector behind a block of glass, measuring the speed of information in glass. With visible light, because the electrons' EM waves lag behind, the tip of the incident wave will make it to the detector as if there wasn't glass, right? But what about after a while - wont information flow slower? For x-rays the tip also takes the expected time as if there wasnt glass. But for information in the rest of the incident wave - wont it make it to the detector faster than if the glass wasnt there? That's what the animation in the video suggests.

@ricomajestic

Ай бұрын

He is using the wave picture of light. He's not talking about photons!

How the direction of light changes , is it due to phase change in medium

@Mahesh_Shenoy

Жыл бұрын

It's got to do with the wavelength shrinking!

@runethorsen8423

Жыл бұрын

@@Mahesh_Shenoy By shrinking you must mean changing. The direction of light changes due to any delta lambda, not just a shrinking one.

Amateur question here: Can the mismatch in phase oscillation be because of the electron having mass and so the electromagnetic force from the photon needs to overcome momentum? Something like trying to oscillate a ball with your hand but with a spring in between? Im probably wrong about the analogy but would appreciate an explanation why. Thanks!

@JB-kf3zk

5 ай бұрын

He has another video that might help answer your question (explains why light also has momentum even though no mass): kzread.info/dash/bejne/lKqu1JSBksW2c5s.htmlsi=sC-wXUsmYrODF862

Wonderful explanation sir ❤❤🔥🔥

@nothingspecial9370

Жыл бұрын

I loved it.

@Mahesh_Shenoy

Жыл бұрын

Thanks, Omal!

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.

Sir thank you for the clear explanation of the speed of light in medium But i have doubt sir ,how the light bend in travel to rarer medium to denser medium please explain sir

I think where I'm lost is that this explains how the phase of the light changes, but not really where the front of the wave is. Your animations showed the front of the light getting pulled back or pushed forward along with the phase, but it's not explained why.

I like the fact that you reply to all the comments. Btw your class 10th science video is helping me so much.😁

@Mahesh_Shenoy

Жыл бұрын

Awesome to hear that, Shail! :)

@GodSahil

Жыл бұрын

@@Mahesh_Shenoy oops! It's ‘Sahil’ not ‘Shail’ XD. I remember my friends used to write my name as ‘Shail’ instead of ‘Sahil’.

@Mahesh_Shenoy

Жыл бұрын

@@GodSahil that was autocorrect!!

@GodSahil

Жыл бұрын

@@Mahesh_Shenoy oh! XD. Np

this was just perfect

A very good explanation, but there's one question. Why is the wavelength in a medium not the same as the wavelength in a vacuum? Since all waves propagate at the speed of light in a vacuum, shouldn't the wavelength remain unchanged after superposition?

@dmitriy4708

8 ай бұрын

It was explained in the video. The wavelength in a medium is a result of interference between the original photons and induced oscillations, so it gradually shifts the peaks of the resulting waves further back or forward (in case of x-rays), therefore apparent wavelenght is shorter or longer.

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?

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.

@Mahesh_Shenoy

Жыл бұрын

Aww! Glad you liked it!

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.

In the double slit we go from EM waves to one photon at a time, and using the wave-function of the photon getting the same (interference) results So what if I send one photon through the medium? Same results perhaps by treating it quantum mechanically?

@Mahesh_Shenoy

Жыл бұрын

A single photon doesn’t have a ‘defined’ path now does it?

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.

In my latest investigations then the electron absolutely has some thing to do with light transfer through materials. Carbon is the most light absorbing material I believe and that has 4 electrons in the outer shell. It is only the second shell from the kernal of the atom. They are probably relatively easy to knock free (carbon is also a relatively good conductor) but some how the energy given back out when the electron jumps back in is in the infrared level (heat). I believe the "Absorbtion bands" for carbon is well into the infra red area (2000-1500nm). Silver is supposedly the most reflective. It has one single electron in the outer 5th electron level that would be very easy to knock free and probably with an energy level that is in the light band. Absorbtion band should be around 430nm I believe and I think that is around green. Nitrogen (the most abundant gas in air) has 5 electrons in the outer shell 2nd shell has absurbtion between 200 - 700nm covering the light band but not nearly as dense as carbon. Oxygen (also a gas with low density is nearly the rest of the air) has 6 electrons in the outer shell and an absurbtion band of 50 - 170nm which is in the UV band. It appears obvious to me (and has since I first learned about Physics and Chemestry more than 50 years ago) that light is influenced by the electrons but I don't know exactly how other than electromagnetically. In regards to electron shell's then I am well aware that they are not in actual shell location but more like a fog like possition. I am only a retired electonic engineer but have put in some thought and have some experience.

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

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 ?

@Mahesh_Shenoy

Жыл бұрын

Really good question! Check out the video by Fermilab on this!

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.

@zyxzevn

6 ай бұрын

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.

So basically light traveling through a non vacuum is like running on a treadmill. You’re still running at the same speed, however you don’t travel as far since you get dragged back.

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?

Are you from khan academy😅😅😅,btw you are my best physics coach ❤ u

From where does electron get energy to oscillate? If electron is getting energy from em wave ,doesn't it effect original wave?