Why light has momentum even without mass?

Light (or photons) is massless. Yet, photons have momentum given by the equation
P = E/c. Where E is the energy the photon enegy and c is the speed of light.
The goal of this video is to gain a deep intuition behind it.
First to understand where the light's momentum really comes from. Second, to use that intuition to derive the equation without using anything quantum. But, by connecting all the fundamental equations of high school electromagnetism.
I first learnt about this from Feynman lectures. You can find his actual derivation in the last paragraph of his Volume 2, chapter 34 - "Relativistic effects in radiation".
www.feynmanlec....

[@Mahesh_Shenoy]

5 FAQs (and counting) and references! First and foremost, here is the source. www.feynmanlectures.caltech.edu/I_34.html#:~:text=We%20now%20appreciate%20that%20light,%CF%89%2Cp%3D%E2%84%8Fk Check out the last paragraph. Now, let's get to some FAQs 1. Wouldn't protons experience a force in the opposite direction? No, when charge flips (from negative to positive), the velocity due to electric field also flips. Hence, the magnetic force direction stays the same. Another way to see it is, F = q (v X B). If both q and v become negative, their negatives cancels out. So, the force direction is independent of the sign. 2. Can EM waves push neutral particles, like neutrons? Neutrons are made of quarks that have charge. So, if you consider that and the fact that force direction stays the same for both positive and negative charge, it should be able to push it. But, I think it would be stretching it. Classical physics is wrong. And we really shouldn't be using at the quantum level. But, the point was to not sell it short. It is still a powerful tool to gain some intuition. My perspective is to use classical physics as a tool to generate some insights. Without these, it would be hard to study any physics. 3. Why would velocity flip when E field flips? What about electron's inertia? We are assuming the electrons are damped oscillators. Wait, how in world can we imagine electrons to be oscillators, let alone be damped oscillators? I am yet to understand that myself. But, I just took Feynman's word for it. :D. [If I try to understand every single nuance, I will never publish any video on such topics. So bare with me]. But, here's the excerpt from Vol 2. Chapter 32, Paragraph 3 👇 "We use a model of an atom or molecule in which the electron is bound with a force proportional to its displacement (as though the electron were held in place by a spring). We emphasized that this was not a legitimate classical model of an atom, but we will show later that the correct quantum mechanical theory gives results equivalent to this model (in simple cases). In our earlier treatment, we did not include the possibility of a damping force in the atomic oscillators, but we will do so now. Such a force corresponds to a resistance to the motion, that is, to a force proportional to the velocity of the electron." 4. Comet tail is caused by Solar wind, not from Sun's light! There are two comet tails. The ion tail (which I didn't mention) is indeed caused by the wind. But, the second tail - the dust tail - is apparently caused by the sunlight. (Radiation pressure). Here are a couple of resources that dig deep into this articles.adsabs.harvard.edu//full/1968ARA%26A...6..267B/0000267.000.html www.sciencedirect.com/topics/earth-and-planetary-sciences/comet-tails 5. Aren't electric and magnetic field 90 degrees out of phase? No! Any EM wave should always have E and B field in phase. Please check out this amazing video that explains this misconception kzbin.info/www/bejne/jWLGhaOngp53l7csi=T2buT-rhWLQGDDZx I will update this list as I see more FAQs. You folks rock. You push me to think and research more! Love it ❤

[@gyro5d]

Mediated to center of everything is Nothing. Nothing has Zero pressure, where the Aether pressure field heads = Gravity.

[@-danR]

A neutrino has no magnetic field and no magnetic moment. Why would it have momentum when it (rarely) bangs into another particle? A 𝛎 with enough energy will even blow a nucleus to bits if it hits a quark dead-on.

[@michaelharrison1093]

Another question that has turned up a lot (and I have tried to answer each time) is in regard to the E and B waves being in phase. Many people have commented that they question if they should not be 90 degrees out of phase? The fact is that fot a traveling EM wave then the E and B waves are phase aligned, but for a standing EM wave there is a 90 degree phase shift which then changes the force from being in a unipolar direction to being oscillitory. You might want to do a video explaining why this difference occurs for traveling Vs standing EM waves

[@AveragePearEnjoyer]

​@@-danR m = 1.4x10^-36 kg

[@owenwilson25]

NO, a comet's tail is blown by the Solar Wind not light, and a shadow effect that can amplify the visual affect as light gases condense in the shade rather than continuing to expand while exposed to strong sunlight.

[@wayneyadams]

1:33 Feynman blows everybody's mind. I have never seen someone who can simplify complex topics like he can. He is probably the greatest teacher of Physics of all time. His language is simple, like saying things bounce around as he makes hand gestures rather than saying vibrations.

[@wayneyadams]

@@IsaacNewton818 I have eclectic tastes, political commentary, Physics (my M.S., which I taught for 33 years), Chemistry (my B.S., which I worked at for 9 years), magic, railfanning, flying model airplanes, painting, woodworking, etc. It's a good chance you will see me on dozens if not hundreds of channels.

[@everythingisalllies2141]

Except that time when he was asked to explain how Magnetism worked. He was actually clueless but pretended that it was the person asking the question that was incapable of 'understanding". This a a common fallacy of logic.

[@wayneyadams]

@@everythingisalllies2141 There is always one person who has some contrary comment to make about any comment. I could write, "It's a beautiful day today." and a yahoo like you would have something negative to say.

[@everythingisalllies2141]

@@wayneyadams Is that your best defense of Feynman? You obviously have not watched that interview. I can't help it if famous people cant afford to admit that they just don't know something. But having "A story" to explain something is not the same as having a rational story. The point is, that people are taught to just accept what people like Feynman say, and they don't bother to consider if its true or rational or not. Einsteins mad beliefs are a great example, probably the most silly claims ever made, and everyone just laps it up without thinking.

[@wayneyadams]

@@everythingisalllies2141 I don't need to defend Feynman. I take him at his word since he probably was unable to dumb down magnetism question to a level where the questioner could understand his answer. Why don't you give me the link to interview and I will watch it myself and decide.

[@scottfranco1962]

The problem is: Feynman is deceased. How are you getting replies from him?

[@THE_FORESAKEN_GAURDIAN]

Defenitely something to do with edo tensai...

[@rishabhsingh2389]

😂

[@Blade.5786]

Just hire a medium

[@paulklee5790]

His energy is conserved… obviously.

[@umapatibhandarifunallover1832]

Heaven

[@itcantbetrueable]

45 years ago high school physics taught me that photons had momentum but not mass. Thank you for explaining how this is possible and bless you for your enthusiasm 😊

[@satyambehera413]

how old r u

[@pythondrink]

​@@satyambehera413 at least 60 years old, I guess

[@pythondrink]

I was never taught this in high school

[@loodstroh4634]

Yes but does photons really exist?

[@pythondrink]

@@loodstroh4634 wdym by this question?

[@robbannstrom]

Well, yes, "it's the magnetic field which gives rise to momentum", but that's only the case since the electron is being pushed - i.e. is *_caused to move up and down_* by the electric component of the EM wave which enables the force equation to come into play. It's the interplay betweeen the electric and magnetic fields in the photon / light wave which allow it to impart momentum on the electron. Having said that, this is the clearest explanation for this phenomenon I've ever seen, so a big thanks to FHP for posting this video! Great work, man!

[@DivineMisterAdVentures]

If you have a question about these as quantum mechanics, see my commentary for a possible solution about 20 comments up.

[@robbannstrom]

@@DivineMisterAdVentures No, I'll refer to the books on quantum mechanics I used while studying QM as part of an astrophysics degree. Thanks anyway...

[@georgioskatsillis2993]

I think he mentions your point at 17:40

[@i.b.blithe3263]

This was an excellent discussion of by Floathead explaining Feynman who in turn was explaining Maxwell... well done. Thank you Floathead.

[@acrylix3073]

Maxwell explaining Faraday.

[@everythingisalllies2141]

Shame that light still has no momentum, because it has no Mass, and no one has ever proved that Light is made of two waves, one electrical and the other magnetic. That claim is actually not even rational, and direct experiments cant support this claim.

[@cosmic_gate476]

​@@acrylix3073 Faraday explaining Archimides.

[@bardsamok9221]

​@@cosmic_gate476Archimedes explaining Pythagoras

[@sqlexp]

I say that this explanation is bs. E^2 = (mc^2)^2 + (Pc)^2 is fabricated just to gaslight people into accepting massless photons. For one, the equation fails for object with rest mass because it gives Pc = (mv^2)/2, i.e. P = (mv^2)/(2c), which is wrong. The last equation he uses only shows that E = Pc, which is true even for massive photons, and it is how the "patched" energy equation was originally fabricated.

[@ryanbaker7404]

Your excitement is contagious! I'm pleasantly learning a lot of new concepts from you, sir. Well done!

[@ArwenAreYouOK]

But his physics is poor, and induces an authority figure - generally a fallacy, but sure, for narrative sake, I’ll give it a pass but you can’t deny the shocking absence of imagination. Think about it, it’s just a back and forth - where the beginning, middle and end are like a template pasted three times over with the old black swan psychological bias thrown in that isn't even appropriate here because the uncertainty in the physical phenomenon is not adequately rare to solicit that very explicit example.

[@arjunarun9147]

@@ArwenAreYouOK quit yapping you don't know physics.

[@keithwilliams2547]

After all these years, someone finally explains this! You are quite a teacher!

[@chrisoakey9841]

I think your first problem is the assumption that light has no mass. Remember it acts both as wave and particle. Not just wave.

[@_ranko]

@@chrisoakey9841 It's not an assumption, it literally has no mass within an incredibly tiny uncertainty range. Just because it's a "particle" (which it technically isn't based on QFT), doesn't mean it has to have mass. You're the one making an assumption here.

[@chrisoakey9841]

you must truly be part of mensa. not an assumption, it has no mass, would be an assumption. if you cant even fully figure out if it is a particle or a wave then it seem pretty stupid to suggest we know if the whatever has mass. after all, it has momentum. it is affected by gravity. its just the light speed equation that heads to infinity that goes no mass. its either no mass or the math doesn't quite work as we know right now. but since it isn't fully categorized, let alone understood how it travels sure, im the one making the assumption. does work, probably has mass. but since we still are using "photon" as a concept because we know so little, maybe it doesnt have mass. lets just accept without thought because einstein..... @@_ranko dont mind that general relativity doesnt quite work on the cosmos or quantum levels.

[@alonewanderer4697]

@@chrisoakey9841idk about the latter half, but i would like to point out that our current understanding of gravity is that it isn’t a force, but more a thing that curves spacetime that means that a photon doesn’t have to have mass to be affected by gravity, as it is not a force :)

[@chrisoakey9841]

@@alonewanderer4697 that is true, that the current understanding is the curvature of space time. however what force makes stuff change direction. space time is never defined. the ether concept seems to be disproven by nicholson morley ether exp. so to change somethings direction takes a force. so what in space time forces us to change direction? general relativity says time, but the force is the same on both sides of the earth. if it were time it would have a relationship to the movement of the earth around the sun. and therefore would be different amounts of acceleration depending on which part of the earth you are on and whether your spin is in the same direction as the earths, or the opposite direction to its rotation around the sun. also it would require the earth to be accelerating outward in all directions at the same time. not a speed but a continued acceleration of 9.8/s/s at sea level. so the curvature of space time says nothing that would create a force. just like if i draw a curved line on a table, when i roll a ball on the table the ball will roll straight unless i draw the line with a thick material that physically acts on the ball. just a curve doesn't curve the ball.

[@DFPercush]

Wow, that actually makes total sense! I've tried to explain this using just algebra before, and it never really felt satisfying. Amazing explanation. Your enthusiasm is contagious, too. :D +1 sub

[@brijeshpatel5017]

You and feynman bring unique and captivating energy to science explanations. Thanks for being so awesome!

[@Dekoherence-ii8pw]

OH MY GOD, AMAAAZING!!! 🙂 I've wondering about this for YEARS. Finally found an answer that makes sense. And it's COMPLETELY UNMYSTERIOUS. It just makes total sense!

[@sushantbagale.02202]

It can be also perceived from DeBroglie's matter waves concept which shows momentum=Planck's constant/wavelength

[@bardsamok9221]

Yes I'm surprised the quantum explanation was ignored, considering it's so key to understanding photons and physics. Perhaps he doesn't understand it, or why its important.

[@casualphysics840]

Hello! I just wanted to say a big thank you for being one of the best educators on khan academy! A lot of your physics videos have been really helpful to me this year and I can feel the effort and thought you put into making these videos. From the smooth animations and the analogies to the crisp delivery of the material, you really make sure that quality doesn't take a hit anywhere. You may feel like I'm flattering you but that's not the case, your contagious enthusiasm for the subject matter manages to sell anything & everything you teach in a way that sometimes even Sal khan struggles with! Keep doing what's your doing sire!

[@Mahesh_Shenoy]

Wow, the message truly made my day. Thanks for putting it so beautifully!

[@casualphysics840]

@@Mahesh_Shenoy You use sketchbook to make videos right? Are there any plugins you use to help with the process or are the extra things like animation added in post

[@fancy_panda_69]

@@Mahesh_Shenoy was going to say thank you but @casualphysics840 said it so beautifully. I haven't seen this video yet (seen some of your wonderful others) and as former undergrad in Physics, look forward to dusting off any special relativity knowledge, hiding somewhere in my brain, beneath the blanket of beer cars. ;P

[@Mahesh_Shenoy]

@@casualphysics840 Yes, sketchbook (with loads of layers). For this video, I did every single visual on sketchbook itself. Nothing else. The only post was zooming in and out at places. I do that in Camtasia. It's my screen capture + video editing tool. Camtasia also has baby animations that we can add in the post. I use it sparingly (didn't use it here). I hate editing.

[@casualphysics840]

@@Mahesh_Shenoy Your layer work is really good :D

[@craigfowler7098]

I have degree in Physics and never really understood this point until now. Well explained and not to complicated either

[@NemoFilHimry]

I love it that you explain your way of thought, which is almost exactly like mine. That voice in the head that self-criticizes every claim, that asks all the time "but why". I too was frustrated by many explanations that only partially answer the question (like most explanations we encounter), but don't really answer the deeper question. This really gave me a deeper understanding, and that itch that existed because of those unsatisfying explanations finally itches less.

[@Mahesh_Shenoy]

I am so glad to see you resonate, buddy!

[@VersaceUnderwear]

@@Mahesh_Shenoy please reply sir, everywhere i see the energy of photon in place of the energy per second that we've got (which i guess is the power) and just momentum in place of momentum per second... so is it like we can use momentum transferred per second=energy transferred per second / c for photons too? ie momentum transferred by a photon=energy of a photon / c which i think should be correct because in this if we put the energy of photon as hc/lambda it gives us a predefined formula momentum of a photon=h/lambda take this question A radiation of energy ‘E’ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (C = Velocity of light) :- (1) 2E/C (2) 2E/C^2 (3) E/C^2 (4) E/C in this if with our formula (ie momentum transferred per second=energy transferred per second / c) do we solve it like, the change in momentum would be double the momentum the radiation has because it perfectly reflects 2*energy transfered by the radiation per second/c or take it all for photons like 2*energy of photon/c (while making the comment) the answers are same which means i was confused in what the question meant by "energy of radiation"

[@nigeldepledge3790]

Yes. This was indeed a surprise. I never realised that I had the tools to work out the momentum of light all along. Thank you for making this make sense.

[@joan4jays]

While all the high school equations were taught, the comet tail to sun relation was never taught 😅

[@Mahesh_Shenoy]

There are some things you learn in school. But, for everything else, there is KZbin :D

[@thecritiquer9407]

​@@Mahesh_Shenoy true

[@prapanthebachelorette6803]

They don’t help you link things together while you’re in school 😂

[@wjiuvdjsvhsnsm]

As a first year physics undergraduate. This video is inspiring to my special relativity final. ❤

[@omarazami7377]

I got my masters a few years ago and I stopped there, I think I want to go back. This video has pushed me in that direction. Feynman delivered and so did you.

[@sohamadak6811]

The enthusiasm in your eyes gives me immense joy. Always refreshing to see someone so passionate about physics

[@perkinscurry8665]

Finally someone has called BS on the so-called explanations using E^2 = (stuff) which have always struck me as mind-bogglingly circular. You've given a brilliant explanation that goes to the heart of the matter. Bravo!

[@optimusmaximus9646]

Love the enthusiasm! I have to say, if anyone get so excited about Lorentz's Law, imagine how excited they will be when they come across the relativistic form of the Lorentz force 👍

[@joe_ninety_one5076]

I enjoy your content, the questions that you ask and answer and your enthusiasm for physics. Apart from the solar wind issue, which has been discussed below, I had a few thoughts about this subject: 1. When drawing an electromagnetic wave you follow a near-universal practice of making the magnetic wave in-phase with the electric one. But, isn't the magnetic wave a result of the electric wave and determined by its rate of change. If so, they should be ninety degrees out of phase. Isn't this also the only way of conserving energy continuously (i.e. by the exchange of electric field energy with magnetic field energy components). Granted, the drawing is just a schematic, but does the pictorial representation affect the explanation in any way? 2. If the magnetic field carries the momentum as described then presumably a positron would be pushed in the opposite direction. Is this the case? I havent found an answer to this, but the Compton scattering formula does not contain charge explicitly, not does its derivation (see Wikipedia). 3. Electrons have inertia, so they don't move instantaneously in a field. They start to accelerate. If the frequency is high, they won't move much at all. If it is very low, they might gain a lot of speed. However, their direction will not be instantly reversed when the field is reversed, they will just be de-accelerated. So, there are a lot of complications in this interaction that your qualitative explanation omits. Is it the case that high frequency photons transfer less momentum to an electron because the electron's mass prevents it from gaining any speed? 4. If the effect can be derived from classical electrodynamics in this way, why wasn't Compton scattering of electrons by photons predicted and fully understood well before Compton received the nobel prize for it in the 1920s, over 20 years after the discovery of the electron? Maybe it was. I'm not arguing with Feynman, by the way, just a bit unsure about what exactly he meant

[@Mahesh_Shenoy]

Love the deep dive. 1. This is an incredible question. What I love about this question is it's actually counter-intuitive. But, it would only be counter-intuitive provided you know enough about the subject. So, the fact that it is counter-intuitive to you is a great sign. (it wasn't for me for a long time :-/). Physics by Eugene has tackled this in great details. Check out his videos. [His channel is famous] 2. Interesting question! And interestingly, the force on a positive charge would be in the same direction as well. Do it do it! 3. All classical derivations are bound to fail at some point. Because, at the end of the day, classical physics is just wrong. And you can't use it explain stuff in the realm of quantum. I think light momentum qualifies to be the realm of quantum. But, the deeper point is that that doesn't mean we sell the classical theory short. What I find absolutely mind boggling is that it is still excellent at providing intuition. 4. My history is rusty here. But, Compton effect is way more interesting. It's a type of inelastic scattering.

[@martinfenner3222]

Over 40 years ago my physics teacher taught us, the drawing of the electromagnetic field in our physics book is wrong, because electric and magnetic waves were shown in phase ignoring completely the 90° phase shift between them. IMHO this is a well known but not corrected fact in nearly all books i know of for such a long time. Not to mention that it's highly misleading about the nature of light and radiation.

[@shubhamkumar-nw1ui]

It is so fascinating to think that Light is a self sustaining unit. When I leaned about this my mind just blew away.

[@MostlyIC]

I really appreciate Joe's questions, I'll add another 5. this explanation doesn't seem to mesh well with light that gets reflected, as this explanation seems to require quite a long time and distance for the light waves to interact with the electrons.

[@L2p2]

Awesome ! This question was bothering me for a long while! Finally you have a video that answers it. Phew! I don't have to take grad school physics classes now just to find this answer. I have only a high school knowledge of physics and I have been trying to understand grad level physics by reading and using intuition to develop a better understading of physics. This channel seems to have the same intent but in reverse that it tries to deliver this understanding. If there are more peoplelike me out there then this will help them. Do keep up this work ! 👏👏👏👏👏

[@lauri268]

Amazing video. This feels way more intuitive than the E=mc^2 derivation that most textbooks use. Thank you.

[@Alex-nq7uh]

I can't explain how amazing this video was. You are such a natural teacher, nothing was left unanswered. I pray you go far so more people can see what you have to offer.

[@danielfarcas751]

This video did what 3 years of undergraduate theoretical physics could not, thank you 🙏

[@hatzisn]

Very nice video and well explained except from the Comets part where the Solar Wind and what this guy carries with him plays also an important role in the Direction of the tail of The comets or better said one of the two tails. Also a force is equal to thrust given to something divided by time it took to give it so since thrust has the same units as momentum according to thrust momentum theorem, you are correct.

[@Mahesh_Shenoy]

The next video will be the most challenging, yet. I want to show how to re discover special theory of relativity - specifically time dilation (although, you could re discover any other consequence as well) - using key concepts of classical physics and thought experiments only. No math! But, with incredible rigour! Will make it live next Thursday.

[@dbtest117]

The devil is always in the details we ignore.

[@mridulacharya8250]

exactly! Going through the whole thought process, the whole journey behind the discovery is all we should seek for...everybody in classroom should rediscover...that's the key!

[@bare827]

Can't wait 😊😊😊

[@petevenuti7355]

I'm confused, the way I understood what you were saying about momentum, does that mean the way it's imparted to a proton results in the proton moving towards the source of light‽ Not away like an electron?

[@charlesstewart4436]

Why light has momentum even without mass? The gist of your explanation is a moving electric charge has a magnetic field and when this is parallel to the magnetic field of an incident electro-magnetic wave the charge is repelled (as if struck by a body possessing momentum). NB in the scenario you are describing the electric field of the electro-magnetic wave is the field dictating the motion of the electric charge. Without this condition it's possible for other possible interesting outcomes. So far as E^2 = (mc^2)^2 + (pc)^2 is concerned this is the same quantity of total energy as is referenced in E = Mc^2. The latter equation is using M which means relativistic mass whereas the former uses m which means rest mass. The latter equation doesn't need to square terms on either side of the equals sign to achieve equality. Each equation can be transformed into the other as the latter is only more compact, while the former uses one term to represent the energy bound up in the mass of a body at rest and a second term to represent its energy of motion (relativistic mass captures in one term all the energy in a body). Plainly if a body is at rest we can see they agree as then m=M and pc=0. However Einstein pointed out these equations make sense even if m=o but pc does not, if we can find a particle which travels at c. Special relativity requires any such particle to have no rest mass but posses momentum p. I think physics buffs need to know both of these quite different reasons why/how we understand light to carry momentum.

[@shabang1330]

Thank you. That makes a lot of sense. A question, however. How does it explain the momentum transfer to a neutral object; a solar sail, for example? And what about a positive object like a proton? Wouldn't the magnetic force be in the opposite direction, toward the photon?

[@mrkoelle]

I was wondering the same things. I’m not a physicist, but I think I’ve got the answers for you. First, “neutral” objects like a solar sail are made of atoms that have a net neutral charge, but in fact are composed of an equal number of electrons and protons, so really they are composed of charged particles that light will push on by the mechanism explained in the video. Next you ask about positively charged particles like a proton. For these, because the positive charge of a proton is opposite to the negative charge of an electron, the electric field will push the proton the exact opposite direction as it pushes the electron, so if an electron would be pushed up, a proton would be pushed down. Now the magnetic field acts on the moving charge. As explained in the video, this produces a force that pushes an electron forward in the same direction as the light wave. For the proton, the direction of motion is opposite AND the charge is opposite. Either one of these things alone would reverse the direction of the force the magnetic field produces, but together these two things cancel each other out, and thus the magnetic field produces a force that pushes the proton forward in the same direction as the light wave. So, light pushes both an electron or a proton forward in the same direction. It might have been helpful if the video had explained this.

[@maulikaryan]

I want to ask from this from the video - What about electrically neutral particles like a neutron? Would it not experience any force?

[@prgnsean]

i just asked this same question. hope we get a response ...

[@mattgbarr]

Neutrons can be electrically polarised, so I'd assume that the large (local) electric field of the EM wave should allow for momentum to be transferred.

[@434mp]

No, the electric and magnetic field depend on a charge q, if that is zero the total forces are zero.

[@mattgbarr]

There is something that you are forgetting here. Neutrons are not fundamental, being Hadrons composed of three quarks which *do* have charge. Under a sufficiently high electric field the neutron should acquire an induced dipole moment; this imbalance of charge should (in principle) be able to interact (weakly) with light's EM field. In reality, a lone neutron should be pretty much transparent to light!

[@redrodtherebel6630]

According to Fyneman’s transactional interpretation of quantum mechanics, other particles simply don’t factor into the equation. Electrons only interact with other electrons, and photons are the process by which they do so, which means photons ONLY ever collide with electrons, and no other particles.

[@Osama_Malkady]

I was surprised when I saw the title of the video. 8 years ago when I was in high school I asked the same question to my physics teacher and suddenly he scolded me and now I got the perfect answer without scolding 😂😂

[@deformityy264]

The amount of energy you used making this video I had to subscribe. That's passion for science

[@thatdood17]

The only problem with this is that the magnetic field and the electron will be in the same plane for just an instant,so my highschool teacher said that its effects are neglected But then I realised,that the time in which the electron remains in the magnetic field is so short that the radius of curvature is infinite,which would then allow the particle to be directed along the propagation vector

[@vwcanter]

Hey, Floathead, you're doing an awesome job with these videos, keep it up. This is the part of the subject that is hard to come by- looking closely at what actually happens with the fields and the charges, and having a clear picture in your head, in addition to the mathematical relations. This is in fact why people liked Feynman's lectures so much.

[@monjilrajkonwar7057]

Great explanation. Your style is awesome. 👍

[@kingplunger6033]

This video is just absolutely great ! Glad I found your channel and I should finally check out Feynman's Lectures.

[@Mahesh_Shenoy]

Thanks man. Everyone should check out Feynman's lectures.

[@kingplunger6033]

​@@Mahesh_ShenoyJust ordered them in book form as I like physical books more than digital

[@mridulacharya8250]

@@Mahesh_Shenoy by feynman lectures u mean the pdf thats there on internet right??

[@Mahesh_Shenoy]

@@mridulacharya8250 Yes!

[@georgerevell5643]

its awesome an so original how you explain your own learning process rather than just state the solutions like a seasoned professor. Also how your not afraid to show you full enthusiasm for this amazing physics, it all adds a layer of mutual intrigue and personal connection with the audience.😎

[@leonhardtkristensen4093]

In a previous video you appeared to me to want to explain every thing with electricity and basically removed magnetism. Here however you need it for your explanation. In my oppinion they are both needed and equally important. By the way I have subscribed a month or so back after having seen a few of your videos as I find you quite good at explaning. I am a retired Electronic engineer and now dabble in trying to understand especially the part of Physics that has to do with understanding and explaning what I have noticed and experienced through my working life.

[@Mahesh_Shenoy]

Great call out. I think I got quite some heat for saying that. :D. In my defence, I did put some disclaimer at the end :D. I agree with you!

[@wayneyadams]

13:08 Falling down a rabbit hole means entering a place where there is no logic, i.e. an insane world like the one Alice encountered which is where the phrase originated. You are not following a rabbit hole when deriving equations or following lines of logic, you are doing the exact opposite.

[@jimroth7927]

Will the derivation you described also work for positively charged particles? If not, the whole argument falls apart, at least for electrically neutral (non-ionized) atoms.

[@gordonlocke5937]

Another “Thought Experiment” might be to consider the effect on a single isolated positron in space?

[@carlosdgutierrez6570]

Unless we are talking about light with extremely small wavelength like x-ray and gamma rays, the photons of light don't interact with the nucleus of the atom, it only interacts with the electron cloud around the atom, it doesn't get to interact with the nucleus.

[@redrodtherebel6630]

Photons just don’t collide with positively charged particles. Only electrons.

[@redrodtherebel6630]

@@gordonlocke5937that’s actually pretty easy to work out. Just reverse the charge of the electron in the diagram, and it’ll have the opposite effect, with the magnetic field pulling the positron in rather than pushing it away, until it ultimately collides with the electron that emitted the photon to begin with and annihilates.

[@HopeRock425]

What about gluons, they carry momentum and have no mass or magnetic field.

[@OrichalcumHammer]

check the pinned comment if it answers your question.

[@ManishaGhogare-qw1wj]

If instead of electron there is uncharged particle then how it will transfer momentum

[@mbrusyda9437]

Photons don't interact with uncharged particles

[@redrodtherebel6630]

That’s the neat part, it doesn’t. Electrons only interact with other electrons, and the exchange of photons is the process by which they do so. Photons only ever collide with electrons.

[@parasharisir]

Does that mean, "electromagnetic waves do not exert force and hence momentum on neutrons?"

[@charlesfreeman4147]

Very interesting! Does this mean the momentum of light is dependent on the electrical conductivity and magnetic permeability of the material?

[@triaswinter296]

I have the same question, sounds weird to me

[@LogeshKumar-vs9uo]

Lambda = h/mv Where mv is the moment um Lambda=h/p P=h/Lamba...1 E = h×new...2 Where mew is the frequency of light And frequency =c/Lambda E=hc/Lambda Interchanging the terms we get Lambda = hc/E Where 1/Lambda = E/hc...4 Substitute equation 4 in 1 we get P=h×(E/hc) h gets cancelled out and we would get the term P=E/c

[@wayneyadams]

It is the combination of the forces generated by BOTH fields that gives light momentum. In addition, think about what happens when one mass exerts a force on another mass. Nothing actually touches in the laymen's understanding of touch, the force is the result of the repulsion of electrons surrounding the atoms. So, it should not be surprising that an EM wave exerts force on electrons.

[@oldskool1977]

Omg! Your voice is so soprano like a 2 year old little girl, especially when you get so excited over electricity and magnetism theories.

[@helbertrodriguez6449]

Ur energy makes me want to learn and learn. I also find this amusing and fun to try to explain n think about it then give it an explanation. I’m just really bad at math and I lack foundations that are essential for this topics. I don’t plan to give up I can learn and learn I wish my professors were like u

[@marcoponts8942]

If you have time, could you explain if it would be possible to do the thing the other way around? I was just thinking about Maxwells equations and yes, a moving charge interacts with a magnetic field, but a "moving" (time varying) magnetic field also interacts with the charge, so I feel like something is being left out in the explanation. I hope you can follow what I mean, even though it is not very well explained. EDIT: and the magnetic field is varying with time, so couldn't IT just create a "current" without needing the electric field at all?

[@tanmantacomama8851]

Wow! Had this question in class recently. What a beautiful explanation.

[@Nobody_114]

Hear is the kicker to Feynman's excellent explanation: in a video you published 1 year ago, titled "Why moving charges produce magnetic (B) field?", Einstein clearly explains that "they *don't* !", explaining how B-field between current-carrying wires is simply relativistic electric (E) field due to charge densities seen in the other wire. This begs the question that an electron reacting to the E-field in an electromagnetic (EM) wave should therefore be unaffected by the B-field inside the EM wave since according to the foregoing explanation, the electron should have no B-field even when it is in motion. So then, if it is not the B-field that affects the electron's motion in the direction of the EM wave, what is it? Surely Einstein would have a relativistic explanation for this, wouldn't he? (I'm being relativistically sarcastic :o)

[@Nuovoswiss]

I think this deserves a follow-up video on how the velocity of an electron induced by the photon's E-field varies in phase relative to that E-field (and by extension, also the photon's B-field). The imparted momentum of a photon can be 0 (transparency), E/c (absorption), or 2E/c (reflection). Or anywhere in-between for various types of scattering.

[@DFPercush]

That would be amazing. It was always a mystery to me why some materials are transparent to different wavelengths. I feel like all the explanations I've heard are kind of hand-wavy. All I know is that electrical conductors tend to reflect.

[@Nuovoswiss]

@@DFPercush In this video he depicted the electron's velocity as being proportional to the photon's E-field, (and also the photon's B-field having no phase lag behind its E-field). Consider a bound electron (in a covalent bond, as in an insulator) exposed to a photon. Rather than its *velocity* being proportional to the photon's E-field, its *displacement* would be proportional. Velocity and displacement are a quarter wave out of phase in sinusoidal motion, so the effect of the photon's B-field would cancel out and impart no (net) momentum.

[@robbannstrom]

@@Nuovoswiss True enough, but don't lose sight of the fact that many electrons in a metal are free electrons, forming a degenerate electron "gas", and it's the free electrons which will tend to be mostly freely accelerated by the electric component of the photon/light wave.

[@MecanicaCuanticaQRAGC]

"Momentum" is a disruption of our space into parallel (Plank lengths), which creates energy, as a parallel divergent effect, which determines the speed of light (without quantum decoherence).

[@Nuovoswiss]

@@robbannstrom Right, that why metals reflect light, though I'm curious where the extra factor of 2 comes in (a reflected photon imparts twice as much momentum as one just being absorbed).

[@sutters7251]

What causes light to move? What gives light its momentum and causes it to move at the speed it does? I’m feeling really stupid, I’m realising my education is sadly, lacking.

[@robertspence7766]

Look up a simplified explanation of Maxwell's electromagnetic equations in 1864. One result is that massless particles must move at the speed of light.

[@meartin]

Feynman rocks audience shocked😮

[@thesquatchdoctor3356]

And he's making sure he gets your wife's number for later

[@meartin]

@@thesquatchdoctor3356 yo wife in me dms

[@adb012]

Hi FloatHeadPhysics, I really hope you see this comment because it is important. I love your enthusiasm, but either I am missing something, or there is something fundamentally wrong with this explanation. (Note, imagine that where I say "electron" below I mean "positron" because for the sake of my own sanity I am taking electric force in the direction of the electric field, not opposite as it would be the case on a negative charge). You are kind of equating the direction of the electric field with the direction of motion of the electron (its speed). And that is wrong. As you mentioned, the electric FORCE is proportional to the electric field. But the force provides ACCELERATION (or, as you said, CHANGE in momentum), not speed or momentum itself. Same as in a mass-spring system, that the mass it at the right of the equilibrium point means that the FORCE and the ACCELERATION will be to the left, but it doesn't tell you whether the mass is moving to the right or to the left (i.e., it doesn't tell you the direction of the motion). If you have an electron oscillating (jiggling) around the equilibrium point, and consider only the electric field for the up-and-down motion, what you will find is that (in the steady state) the electron will be moving down when the up lobe of the eclectic field starts, and it will spend 1/2 of the up lobe moving down but decelerating until it reaches zero speed exactly where the electric field reaches its maximum, and form there it will reverse its motion and keep accelerating up hence moving faster and fasted back the the equilibrium, which it will reach exactly as the electric field goes back to zero. Then the down lobe of the electric field starts and exerts a downward force on the electron, but the electron has inertia so it will keep moving up as its slows down reaching the maximum up deflection and zero speed exactly as the down lobe of the electric field reaches its maximum, and so on. Now if you apply the magnetic force to it, half of each magnetic lobe (both up and down) the electron is moving up and the other half it is moving down, transferring zero net magnetic impulse. Now, OF COURSE that light (and hence photons) have momentum. But your explanation just can't be the correct one, unless I am missing something. I don't know what the correct explanation is, but I suspect 2 things: a) When the electron jiggles up and down it creates its own magnetic field, because an electron moving in an electric current and electric currents induce magnetic fields and, in particular, variable electric currents induce variable electric fields. I suspect that that electric field created by the moving electron will have something to do with the non-zero-on-average net force (and hence non-zero impulse) you are looking for. b) But I still suspect that we cannot get to the momentum of the photon just with high school electromagnetism. I suspect that we will still need relativity in some shape or form to make it happen. For example, a concept that was used years ago but now is largely abandoned is that of the relativistic mass (mass at rest times the relativistic coefficient gamma, which depends on the ration of the speed of the object vs the speed of light). If you apply a constant force to an object you will see not a constant acceleration, but it accelerates less and less as it approaches the speed of light, giving the impression that the mass of the object increases (only way in traditional Newtonian physics for the acceleration to diminish under a constant force). You need an infinite force to accelerate a non-zero object to the speed of light. That means that an object at 90% the speed of light has much more than 9 times the momentum than the same object at 10% the speed of light. Again, the apparent mass (or relativistic mass) is much larger than its rest mass. However, you can do the following: Take a mass at rest m0 and put it at any given speed v. It's momentum is not going to be m0*v but mr*v, where mr is the relativistic mass m0 times gamma. Now you can do the following exercise: What would need to be the rest mass m1 of another object that goes at another faster speed v1 so as it has the same momentum than m0 had at v? And you will be able to find it. It will be a lower mass, of course. If you keep doing that and look for the limit with v going to c, you find the following: The rest mass goes to zero, and gamma goes to infinity, so you get a zero-times-infinity indeterminate limit that has an actual limit. In the limit, you will have that a zero mass going at the speed of light with a non-zero and a non-infinite momentum will have indeed a relativistic mass mr. You will find one value of such mass for every momentum, because the momentum is simply mr*c. The rest mass of such object is zero (because remember mr = m0*gamma, and here we are in a condition where m0 is zero and gamma is infinite). These days apparently we don't use the concept of relativistic mass as much but we use other concepts like relativistic energy and relativistic momentum with equivalent effect.

[@Derrekito]

Aren't the directions of comet tails affected by other types of radiation (e.g., electrons and protons) rather than light? Edit: I looked more into this. The ion tail (or gas tail) is influenced by charged particles and points directly away from the sun. The dust tail is influenced by light and doesn't usually point *directly* away from the sun due to a combination of the direction the comet is traveling and radiation pressure (i.e., light momentum?) - anyway I hope I got that right.

[@gabrielpus-perchaud9063]

There is still something that I don't understand... This explain how light can push electron in the direction light is traveling, but matter is made of small electrons and massive positively charged nucleus right ? Following this reasoning, positively charged particules should be pushed in the opposite direction, and since nucleus are more massive than electrons, light should attracted matter, so where am I getting it wrong ?

[@Mahesh_Shenoy]

Check the pinned FAQ comment

[@gabrielpus-perchaud9063]

@@Mahesh_Shenoy thx !

[@hardpanchal2821]

Its always a good day when you upload, and OMG this was absolutely amazing! This took me to a another world, and the way you explain is already out of this world, FAR FAR better than anyone I have looked upon. I truly love physics and you are just increasing my love for it. Saying Thankyou is an understatement... I truly appreciate all your efforts, and I would absolutely LOVE more content on quantum physics and Relativity. Much Love!

[@holidayrap]

Perhaps light DOES have mass and we just don't have the instruments sensitive enough for it to be measured. In order to understand physics and all its laws we must accept the fact that we DO NOT know all of physics and its laws. Thus we must approach its exploration with a factual AND theoretical mindset.

[@paaabl0.]

What about particles without charge? Awesome video, btw. Amazing energy!

[@tyruskarmesin5418]

I don't think particles without charge interact with electromagnetic waves.

[@skat9000]

Matter is made of atoms and atoms certainly have electron clouds, so this explains 99% of classical Physics. For more exotic no charged particles, lets wait for next videos :-)

[@golden_smiles]

@@tyruskarmesin5418 Meanwhile photons can pass a momentum to neutrons.

[@compulsorilyconspicuouscat]

oh my gosh :O this was probably the best explanation i've experienced, i feel enlightened, and i want to read some of this Feynman fellow- and i'm not even a physicist, i'm a mathematician X3

[@KAZVorpal]

Your explanation about a comet's tail is problematically incomplete. The primary motivator of both a comet's ion tail, and its separate dust tail, is solar wind, not sunlight. Sunlight is a secondary factor, and only for the Dust tail.

[@larzcaetano]

A few questions arise inside my head every single time I see someone mentioning that light propagates due to the interaction between the electric field and magnetic field. If we go back to how things started, what we could actually measure was the interaction between two charges (or two charged bodies if you prefer). We then tried to generalize the entire thing by fixing up a charge Q in place and changing the other charge, Q'. By doing this you can see that F = (something)Q'. We can then see that this “something” is what we call “the force by unit charge”. This is called electric field and it, alone, doesn’t make any sense or can’t really be perceived (so as the magnetic field). It is a generalization of the electric force felt by a charge Q and Q', for Q, which is actually the phenomenon itself. Going back to how light presumably “propagates due to the electro-magnetic field”, it doesn’t really make much sense to think of it because there is only a single, hypothetically, charge there, which is the photon itself. This is why I try to think that there is something else which can explain how light really works. Defining it through electric and magnetic field is maybe just a coincidence, deep down… and ah, it works. Great video, as always.

[@eldunari6676]

2:03 I’m still in high school so my opinion means nothing here, but the way I see it, mass times velocity is a way to solve for something’s momentum, and not being able to solve for something’s momentum does not mean that there is no momentum. I think there’s a logical fallacy describing this. I haven’t even watched the video yet, just wanted to write this.

[@odio_stationofficial3420]

❓❓❓But why is it even called momentum, it can't even touch, can't move something electrically neutral, like neutron, why then will momentum not transfer into it due to Momentum Conservation? E/c should then give speed of neutron....but we all know, neither of magnetic or electric fields are gonna move it...??????????????? Momentum should be unbiased for all particles right Mahesh? ❓❓❓

[@narfwhals7843]

It is called momentum because it can affect the momentum of other objects. How momentum of changed has always depended on the interaction. All things can only change the momentum of things they can interact with. Photons interact with charged particles. That's what "having charge" means.

[@jitendrarath5615]

conceptually explained. Nice

[@Urstrulyharsha.srk2277]

i watched many vids of urs from this channel and khan academy and they r amazing...ur the best sir...pls keep on dng vids...your vids are really interesting and amazing :)

[@DaHuuudge]

Great video! Question: if you shine light on a *positively* charged particle (say a positron or a lone proton), will the particle be pushed in the opposite direction of the light beam?

[@sebastianhenckel6440]

No! Check it out, the change of velocity direction and the change of charge cancel out in the cross product, so the positive charges also get pushed forward. This is important, otherwise no net moment would be transmitted.

[@ArwenAreYouOK]

Whoa whoa whoa. You got it wrong, like I don’t where to begin… The equation (E = mc^2) is often misconstrued as a formula for all kinds of energy. In reality, it applies to an object at rest, and it equates the rest mass (m) with its rest energy (E). For a more general case, including particles in motion like photons, the full equation is (E^2 = (mc^2)^2 + (pc)^2), where (E) is the total energy, (m) is the rest mass, (p) is the momentum, and (c) is the speed of light. For photons, which have no rest mass, the equation reduces to (E = pc). Momentum for particles moving at slow speeds is p = mv, which is an approximation for low speeds and essentially stems from the above equation when (c) is much greater than (v). Can’t you see it? Jeez. The speed of light in a vacuum is constant (c) but it can appear to travel at different speeds through different media due to scattering and absorption processes. However, its fundamental speed in a vacuum remains (c). Light is a self-perpetuating electromagnetic radiation. This is why it has momentum, despite having no rest mass. Finally, again: the point about (E = mc^2) is about “rest energy” & energy mass equivalence. It is not even an equation that you can chuck in numbers and calculate - it’s photons with no inertia. For particles in motion, including photons, the total energy includes a kinetic component, which in the case of a photon is its only form of energy as it has no rest mass.

[@Mahesh_Shenoy]

Thanks for that detailed explanation. Can you point out which section of the video did you find really wrong?

[@imnewtothistuff]

Can't YOU see it? Jeez, Light doesn't travel, it propagates. photons don't exist. There is nothing moving from here to there. There is no mass. To every action there Is an equal and opposite reaction, light propagates through the aether field, Just like sound propagates through the air. Nothing is moving from here to there.

[@ArwenAreYouOK]

@@Mahesh_Shenoy Nit picking dry math inconsistencies is boring and clearly some people don’t like that. And it’s because the synthesis of what you are saying is true but it’s affirming the consequent…like as an analogy - you can explain compounding correctly yet end up with the wrong rate of interest. You can also say equilibrium is the same as stability, which to most people is perfectly ok, but in mathematics, nope. But w/e I am drunk and squinting my eyes just to avoid typos. GN.

[@John_Skin]

Just asking because I'm interested, but isn't v=c In that case, wouldn't FB=Fe be correct as well?

[@thescouselander5531]

The point on comets is invalid because the solar wind consists of massive particles in addition to light so one cannot assume it's light moving the comets tail. Secondly, if momentum is described mass x velocity but an adjunct is added to take care of momentum in a wave this is describing something else vs the original definition. I would ask if all momentum is energy is all energy momentum? I'd suggest not and the reason light has momentum is because physicists are bad at semantics and are trying to describe things that are similar but not the same using the same word. Try a thought experiment maybe. Suppose there is a solar sail in deep space well away from the solar wind. We fire a powerful laser at it but what happens - does the sail accelerate or are the electrons around the atoms of the sail excited resulting instead in light and heat?

[@tanmoybhakat7912]

Love this explanation, superb video ❤❤❤

[@cozajeden]

The thing about comets. Solar wind, not light...

[@AdityaKadamMechanical]

Fi ally my doubt got solved after 14 years. Thanks Bro

[@Xayuap]

I would like it to find the number mathematically. ¿could it be done?

[@MichaelBristow137]

The problem with the comet explanation is that the solar wind is made of particles in addition to the light...

[@dulli41]

Actually I think this is wrong. It is because the charged parical is moving the most while the magnetic field flips and so the pushing and pulling forces cancel out. MAthematically this can be shown with a simple example: Looking at a planar E-M-wave traveling in the z direction with angular frequenzy w and wavenumber k: E(t,z)=e_x E_0 sin(k*z-w*t) B(t,z)=e_y E_0/c sin(k*z-w*t) Here the importand thing is that the ozilation of the E filed and the Bfield are in phase which they have to be to statisfy the maxwell equations. An electron starting at t=0 at the origin experiences the force F_e(t)=E(t,0)*e this leads to a exeleration via F_e=m*a -> a(t)=e_x E_0 e/m sin(-w*t) here m is the mass of an electron Integrating gives the speet of the electron at any time: v_e(t)=e_x E_0/w e/m cos(-wt) with this we can calculate the magnetic force F_m(t)=e (v_e(t) x B(t,0)) =e_x x e_y (E_0 e)^2 /(w c m) cos(-wt) sin(-wt) =e_z (E_0 e)^2/(2 w c m) sin(-2 w t) where in the last colum I used the probertys of the crossproduct and some trigonoic identity. Anyways this Force oszilates with twice the frequency of the E-M-wave around zero. Therefore it is a sensible thing to do to take the averige for calculating the resulting force. This is zero. If you want to say: yea... but what about circular polarisation. v_e is allway paralel to the magnetic field. So the magnetic force is allways zero. If I made any sign errors I am sorry.... but -0 =0 so the result stays true

[@jimmywatson7950]

Yes, you are right. The electric field wouldn't even get the chance to give an oppsite force. These fields are only present at a point. So when the first electric field strikes electron will move up and there will actually be no magnetic force acting because even the magnetic force was also present at that one point So my conclusion is that the electron will just move a bit diagonally I have not the mathematics. I will do it now lets see my assumption is correct or wrong

[@hashashash]

So if i shine a light on a proton, it will get sucked in?

[@akashpremrajan9285]

You can repeat the calculation with a proton, and you will still get the same result. Light pushes on any material that has charged particles. Positive or negative, does not matter in this case.

[@ianwilkins3009]

That's amazing thank you. The process of photons having momentum - such a beautiful and simple process, one I didn't understand before seeing this video. I just had some of those same revelations you explained. One question I do though still.... if a photon was to collide with a free moving neutron, would momentum still be transferred? (ie - a neutron or another charge-neutral fundamental particle ..?) thanks again, I love your enthusiasm.

[@whitetomato]

I think it wouldn't interact with the neuron, since it isn't charged, making it appear transparent.

[@manputty4u]

How do we explain momentum of light in a vacuum with no electrons?

[@amkessel2014]

Great video. Love your content, and an happily subbed now. BIG question about this explanation, tho. Wouldn’t the momentum transfer then be in the opposite direction (e.g. to the left in the video’s example) for a positive particle, like a proton? And so then wouldn’t the net momentum transfer be zero for an atom with neutral charge? To put it another way, does light only transfer momentum to charged particles?

[@Mahesh_Shenoy]

Check the FAQ. It doesn't.

[@ELYOUSFIWORLD]

But concercing the illustration of the magnetic field causing Momentum, if for example the direction of the electrom is down, and the magnetic field is on the right, then wouldn't the magnetic force be opposite to what you said ? You showed only 2 possibilities. I'm I right ?

[@OrichalcumHammer]

magnetic field gives direction, electric field gives energy. @ 17:40 Also check the pinned comment

[@atklm1]

Could've asked Feynman instead of momentum that what exactly is mass. It's energy. Photon is a disturbance in the electromagnetic field and is in itself a tiny package of energy. Energy cannot be created nor destroyed, but photon can turn into a particle with mass. Energy is not destroyed, but converted. Mass can turn into energy and vise versa. Energy and matter are different expressions of the same thing, just like time and space. Energy is relative, just like time. Energy cannot exist without time and matter cannot exists without space. Inside a black hole, energy turns into mass, time becomes space-like and space becomes time-like. All gravity is really curvature in time more than curvature in space. Since energy, matter, time and space are so entwined, even the most seemingly meaningless particles have their effects. Even neutrinos, while having barely any interactions on anything, do have mass. And no matter how insignificant, over great distance and time, they have a huge and important impact on shaping the large structures of the cosmos. This quantum vacuum bubble we call the universe surely is like a clockwork, a strange and complex machine.

[@Mahesh_Shenoy]

Will do a follow up on mass!

[@manojaggarwal2773]

Nice thinking, but photons do not have charge, and particles like neutrinos are not disturbances in the electromagnetic field yet they also have momentum. Neutrinos don't even interact with magnetic fields (directly at least). In fact, the magnetic field is actually the same as the electric field (the electromagnetic field) - they are not independent effects. The simple truth is that whenever energy is in motion - it has momentum. It has nothing to do with its mass. In fact, mass is merely a measure of energy - you actually don't need the concept of mass - it just makes things easier for us. We just perceive trapped energy as mass. E=MC2 is the wrong way to look at it, it's M=E/C2 - that is, Mass is a manifestation of energy, not the other way around. Energy (a particle for instance) is a disturbance in some field, and when that disturbance propagates, it carries momentum because momentum is just energy in motion. Another way to look at this is just as an wave carries momentum through the surface of the ocean even though no particle is moving forward - it's the disturbance itself that carries the energy (momentum).

[@DivineMisterAdVentures]

Great critique and co-analysis. You have a great intuition. I made a parallel argument from Quantum Dimentionality that I have worked to understand clearly about 30 comments up.

[@ChienChangChen]

I remember in your past video you said the magnetic field is actually electric field from view of relativity. Then how do you explain the magnetic field from the light by relativity? Length dilation didn’t work here.

[@DivineMisterAdVentures]

See my commentary for a possible answer about 10 comments up.

[@manharshah6483]

Hello, you are not showing E is out of phase by 90 degrees to H. During up of E the H will have part in the page and part out of the page making average push to electron zero. So your explanation doesn’t hold.

[@khmzrun1]

in EM waves electric and magnetic waves are always in phase

[@will.braveheart]

Question-In this video you seem to be referring to a photon (how can something without mass has momentu). But throughout your diagrams show a particle with negative charge (electron). Do photons experience the same effects of the magnetic field that electrons do without having a charge or am I missing something?

[@daviddanielfontaine8116]

That's what I'm wondering.

[@classictutor]

Thank you for your logic, intuition and derivation. They are excellent. One thing I would like to point out though is that there is not an imaginary electron and therefore an imaginary velocity nor an imaginary F(sub B or a magnetic force). So it seems to bring us back to the square one. Perhaps once the prop (electron) is used, then we would have to remove it and then the force has to arise out of the interaction of electric and magnetic fields, but that's hard to see in the electromagnetic wave of the light itself.

[@DivineMisterAdVentures]

If you like these as quantum mechanics, see my commentary for a possible solution about 20 comments up.

[@jimmywatson7950]

I am really happy that I have known this but the only problem with me is that why should the magnetic field and the electric field be dependent. Why can't we make a magnetic field independently and electric field independently and combine them so that they do not obey the equation B=E/c In simpler words, I want you to derive the equation B = E/c. It would be of great help. Overall, it's great, and I am really impressed that you put on so much thought on this. I also watch your videos from khan academy. I hope you will get the time to reply this comment. Thanks 😊

[@audiblevideo]

Math and Physics are not magic there are rules and things derived from those rules. The symbology is what throws most people off because its like learning a spoken language which has to be run through a number of translators so that meaning can be found in the mapping of what is already know and what is to be learned. You have done an excellent job of "translating" and showing the math and physics -- SUBBED

[@tomc6122]

Hi, Nice job with the explanation. You have nicely described the action of the electron interacting with a light wave. Perhaps, you have an equally enlightening description of how the light wave is transformed by it's interaction with the electron. Also, consider the possibility that the electron was only grazed by the light wave - as opposed to a direct impact.

[@mbrothers123]

This is INCREDIBLE; your personality is AMAZING and you make learning soo infectuous

[@wayneyadams]

F = qBv is the MAGNITUDE of the magnetic force, NOT the magnetic force which is a vector quantity. You need to be precise in your language, the vector equation DOES NOT become a scalar when taking the cross product (outer product).

[@DivineMisterAdVentures]

I left a detailed commentary that you should see and I would appreciate your comment.

[@wayneyadams]

@@IsaacNewton818 There is nothing evil here, it is simply an erroneous statement. Would you rather remain blissfully ignorant, or learn the truth?

[@evanwilliams7376]

Good video, the part I am struggling to connect is the fact that you assume that the electron is traveling in a specific direction based on the electric field but the electric field doesn't give it velocity it gives it acceleration. If someone can cennect this dot for me I'd appreciate it

[@Mahesh_Shenoy]

Check the FAQ pinned comment!

[@ItsHaruki]

Is this the reason of photoelectric effect?

[@tinglingchemistry]

U can't have pink dog btw🐕

[@UdayKumar-es7ft]

What if the electron is at rest initially??

[@rahulmeenaofficial]

Are you the guy who made the khan academy videos. Your voices sounded very similar.

[@Mahesh_Shenoy]

Yes. :)

[@rahulmeenaofficial]

@@Mahesh_Shenoy thank u you are the reason I passed my 12th board exams.🙃

[@LenBloch]

This is excellent, but it leaves me wondering about momentum transfer to uncharged particles, such as neutrinos.