What is a rainbow?
Вставка
- Опубліковано 4 січ 2021
- This video explores the physics of rainbows by considering how light is refracted as it passes through water droplets. The formation of both primary and secondary rainbows (double rainbows) is explained, as well as the formation of the dark band known as 'Alexander's band'.
In his poem of 1820 entitled Lamia, John Keats complained that cold science had destroyed the magic of nature, conquering all mysteries by rule and line, and that Newton, through his work on optics, had un-weaved the rainbow. In this video I would like to show that Keats was misguided, and that by understanding the physics of rainbows, using only the basic tools of geometry and imagination, the experience of seeing a rainbow is enhanced, not diminished, and that the pursuit of scientific knowledge only ever adds to the magic and mystery of reality. It never subtracts.
References:
The Feynman Lectures - Richard Feynman
For the Love of Physics - Walter Lewin
Applied Project - The calculus of rainbows (www.stewartcalculus.com/data/...)
You can help support this channel via the Physics Explained Patreon account: / physicsexplained
You can follow me on instagram: / physics_explained_ig
You can follow me on Twitter: / physicsexplain1
Found this channel just now. Feeling lucky.
Glad to hear it :-)
I have now watched my second video and think the same. What luck I have to have encountered this content.
Same. This is awesome.
lucky day for me aswell
Yes, these videos are gems. Nice to see the new ones appearing and the view/subscriber count going up too ... might persuade _Physics Explained_ to keep making them.
I love the level of details you dig in your videos. Being an associate professor of physics myself I have listened, read and taught this many times. But the "enhanced intensity of rays" around max. angle nuance has always escaped my attention. Thank you for the quality work and keep it up! Best regards from Turkey...
Wow, thank you! I really appreciate the comment. All the best from London, England!
cheers from Turkey too , hocam nasılsınız ?
The obligatory quote: "...the science knowledge only adds to the excitement, the mystery and the awe... It only adds. I don't understand how it subtracts.”
― Richard P. Feynman,
Legend
This is technical knowledge with a whole lot assumptions and presuppositions lacking any sort of context of time and space of real life . Science is knowledge that stands the test of time and this is not it as technical knowledge is always changeable. You are just confusing technology and science as almost everyone does and perverting science in the process.
@@gledatelj1979 This is the only explanation of the rainbow that ever stood the test of time (or any other test, for that matter). This is science and technological applications are not even discussed. Before you come lecturing others on things you are incompetent of, learn to use punctuation and to write complete sentences.
I thought it was Richard Q. Feynman who said that. 😛
You beat me to it!😅🤣
Best physics channel I’ve ever seen. Lots of channels avoid any maths fearing to lose viewers ; others do not refer to the history explaining how theories were developed. And just these elements are necessary for understanding. And understanding increases the mind and brings joy. Thanks.
Starting a degree in physics soon (October) I must say I love your well made, articulated and presented videos. Especially how you show the maths, equations and thought processes for proofs; certainly helps me stay sharp in my physical intuition.
Thanks for taking the time to leave a comment. My aim when making these videos was that a bright high school student should be able to follow the logic and the mathematics. Too often the mathematics is omitted at school, and yet often (for me at least) it helps with the understanding. I am really pleased that you find the videos helpful and I wish you the best of luck in your physics degree!
@hugh mungous, agree, the maths is really important. Otherwise it becomes what I call "glossy science", which I read for years and never felt satisfied until I finally started studying physics formally. Good luck with your studies and hope you find it as rewarding as I did.
i really envy you, i studied physics 20 years ago, one of my brothers work at CERN projects and I decided to move to software engineering, but my heart always bring me back to physics videos lol. I want to share with you something I learn during my career, the really most important part is hard work, you will meet lot of smart people, some of them extremely smart, but those who will be successful are those who work harder than others, at the end hard work and constant will define who is really great. never ever stop attacking problems, even if they seems impossible at some point, just continue learning and attacking again, good luck.
Nobody has ever explained it this way... Amazing.. If only i could give thousand likes... Bravo
I appreciate that you take time to explain the subject in a deeper manner but still targeted for laymen like myself. There's not that many channels like yours in youtube
Thanks for the kind feedback, much appreciated
After watching this stunning presentation, I am reminded of Richard Feynman's comments regarding a scientist's perception of beauty in nature. "An artist friend holds up a flower and says, 'Look how beautiful it is,' and I agree. Then he says, 'I as an artist can see how
beautiful this is but you as a scientist will take this all apart and it becomes a dull thing'... Although I may not be quite as
refined aesthetically as he is... I see much more about the flower than he sees... beauty at smaller dimensions, the inner
structure, also the processes... It only adds. I don't understand how it subtracts."
(Richard Feynman)
Another insanely good video :)
Keep up your amazing work!
Thank you the great explanation. I had an entire section of an assignment based around this topic. I have yet to find in depth explanations like yours, and i really hope you will keep making these videos!
Great content! Your explanations are perfect and filled with interesting details. You're doing some good to humanity !
Damn i was hoping to binge another channel
Whatever ill sub and wait
Good stuff man
Thanks for great videos!
I don't know if it matters to you... but when someone asked you to drop ads, you agreed for some reason and left only one slot. I believe you deserve more following and a bit more ads is the least we can do to support your work. Those who don't want to watch ads can always buy youtube subscription and enjoy the ads-free experience.
A very good balance bwtween the necessary mathemaical complexity and the simplicity of physica of rainbow formation. This video not only sufficiently explains the process of rainbow formation for a highschool grader but also provides clues for deeper studies into this topic. Great job!!!
Beautiful explanation - thank you!
Glad you enjoyed it!
Best explanation for this phenomena I've ever found. This video is amazing! :)
What a gift.
A truly enjoyable channel on UA-cam ... I point these lectures out to my son ... hoping enough is understood, that he would study more out of interest. Thank you ...
Zero dislikes exactly how it was supposed to be.
unfortunately there are 4 right now, I suspect they antiscience. (1.1k likes as of now tho)
I hope you know that people disliked this video because of this comment 🤣
This was the last video made so far and I only just discovered this channel >/* . Make more please! These videos are insanely good.
Thank you for this accurate description. Far too often, when rainbows are explained for non-physicists, it goes beyond being just inaccurate. It actually teaches some of the underlying concepts incorrectly. The most egregious might be that the bright bands occur due to Total Internal Reflection occurring at just one angle. With no reflection occurring at other angles. The truth is that, at every encounter with the water/air boundary, a small fraction of the light is reflected while the rest transmits.
Here is the non-physics explanation that I like to use (all numbers are approximate):
1) Rainbows are created by all of the light hitting a raindrop, not just light at one spot. So any explanation that draw just one ray of incoming sunlight is already inaccurate.
2) The drop reflects this light back toward the sun in a ~40° wide (from the center) beam, much like the mirror in a car's headlight or a flashlight/torch.
3) But there are two significant differences:
3A) The width of the beam varies with the color of light, extending out to 42° for red.
3B) Each color is much, much brighter in the outer 0.5° of its range.
4) This places the bright-red part of the beam between 41.5° and 42°, with (essentially) no other colors of light in that range. So we see a bright red band of color there.
5A) The bright orange band is between 41.25° and 41.75°. Half of it overlaps the red band, but there is some red under all of it.
5B) The bright yellow band is between 41° and 41.5°. Some overlaps the orange band, but there is red and yellow light under all of it.
5C) This continues, making each color toward the end of ROYGBIV appear paler that the same color in a spectrum, until we reach white light inside the violet band.
For double rainbows:
7) Because there are two reflections, the beam is reflects _away_ from the sun, and is ~130° wide.
8) The red band is still on the "outside" of this beam, and the overlapping occurs the same way. But because the width is more then 90°, the beam wraps around the top of the sky and is seen - _upside_ _down,_ not reversed - about 10° above the primary rainbow.
This channel should have more recognition!
hello, i can see you have a lot of followers who love your content, that is so cool, specially as you help to spread knowledge in physics.
Can you do a video about double slit experiment and the quantum eraser? for me is extremely fascinating.
Wow. Out-stan-ding. Your videos are incredibly good. Thank you for improving the world, you really make a difference!
Wow, thank you!
I think some cases of physics remove the beauty of perceived reality. Like when Steve Mould and the laser guy were looking at a laser interacting with a soap bubble, and it occasionally showered the room with hundreds of little dots. After some careful examination, they deduced that it was caused by the disco ball on the ceiling.
Jokes aside, nice explanation! I think I’d be interested in seeing a graph or at least equation that predicted the spectral radiant intensity at a given angle, to see how much each colour dominated. Because technically the Sun’s light is dominated by green light, but our eyes see it as white because it’s a broad peak. Though it’s probably just got an f(solar black body) multiplied in front of the equation in the first place.
You are doing a great work of vulgarisation again. Thank you for creating those fascinating videos.
Thank you very much for the understanding. the best explanation i've seen so far.
I did enjoy the journey around the raindrop. Many thanks for such vivid description of such a vivid natural beauty
I watch three of then now. It's excited to watch this channel series video
Awesome 🎉🎉🎉 please keep posting such conceptual and mind-blowing videos..
Best regards from India..
This was just the right amount of info needed to make this info understandable, great work!! My question is,can the primary and the secondary rainbows be reversed?if yes,would the "alexanders band" actually appear to be a brighter area?
Excellent video thanks! Could you expand it slightly to cover the change of curvature of the rainbow and why pilots remark that it is possible to fly through the bow as if it is a circle. As we are all addicted to animations now a video showing changing observer position would be very interesting. Thumbs up and subscribed.
Great suggestion!
Underrated video compared to your others.
You are an explanatory genius.
Hope your gets the recognition it deserves
didnt skip all the adds to show support...i really enjoy this
Much appreciated, thank you
I love this channel!
Glad to hear it!
It was at 10:38 when I had a eureka moment. So awesome! Thank you for sharing.
Great explanation!
Most comprehensive explanation of this incredible phenomenon in nature.
The best Physics explanations
Perfect timing. I want to learn more about physics this year
Glad to hear it!
That was genuinely incredible! 😲🌈
thanks dude , that was realy clear
Does this mean there are more rainbows at greater angles that just get too faint to see as the reflections get less and less likely? Or is there a reason our idealized raindrop can only reflect twice?
This was a surprisingly interesting video! It made me think of the chapter The origin of the refractive index in the Feynman Lectures and the Corpuscles of Light talks.
I've definitely seen triple rainbows. I reckon the intensity is just too low to perceive any more than that, though I can't say if there's another physical reason related to the geometry of the water drops.
Brilliant channel.
This is very well done.
Excellent content recommend to all to watch 👍🏻👍🏻
Much appreciated
I had always wondered what causes the secondary rainbow, and now I know. Thanks!
My pleasure
Excellent presentation!
Thank you kindly!
Highly underrated channel
It would be nice to see the picture of the rainbow through red and blue filters, and the plot of intensity of the light for different wavelengths versus the rainbow angle.
I agree, that would be interesting to see!
....and now I know!! Except for the math bits, that just gave me a headache but the clear explanation of the 'production' of a rainbow was great!....
Now to wait outside until there is a rainbow & my neighbours come out & are all, "Ooooh!" & "Aaaah!" & I can say..."I know why that happens!"
Thanks for the feedback, glad you got something out of it
Another excellent video! As a physicist, my appreciation of rainbows is definitely enhanced by this explanation.
Many thanks!
You can make a second video(part 2), which will deal with the wave properties of light, explaining the extraordinary rainbows.
Now rainbows are more beautiful. I loved it.
Awesome ! Thank you ! I knew only the basics of the rainbow so this is really nice.
I also knew that prismatic effects like this separate the colors but never thought about the refractive index changing with frequency. WHY is that ? I mean, is the permittivity and/or permeability of the medium (in this case, water) different for different frequencies ? I usually think of these two characteristics for speed of light or electromagnetic radiation in a vacuum. Or is it due to something else in a medium like water, glass, etc ? Maybe this should be obvious or not.
Thanks for the kind words. Regarding your question relating to refractive index, I would recommend watching the following fantastic video: ua-cam.com/video/R8nRfs7JCOI/v-deo.html
Ahhh... A new relevant word ! Dispersion ! Thank you ! I knew you would come through ! :)
Beauty is meaningless without inquiry.
Pithy but not true
@@jphanson Couldn't agree more.
Here is what I was hoping this video would explain but didn't, and if it did and I missed it I apologized: Why do I see one rainbow instead of a trillion little ones? I'm still unclear how I see 1 giant rainbow from a collection of droplets. Are the droplets close enough that they act like 1 giant drop?
I appreciate the content and subscribed. Thanks and keep the great content coming!
Awesome video.
Physicist here. I love you and your poem.
This is the best explanation I’ve ever seen on how rainbows are formed and why there is a secondary rainbow. I would like to ask the question, however, why, when observing a rainbow from an aircraft looking down on clouds, the rainbow angle is significantly smaller than 42 deg?
The angle is still 42 degrees, it's dependent on the angle of the sun
You're right, those aircraft "glories" are less than 20 degrees angular width. Apparently they are formed in a much more complicated way than regular rainbows, and the details were only worked out in the 1970s. That's according to this web reference, but I couldn't find anything further: web.archive.org/web/20070814050142/www.polarization.com/rainbow/rainbow2.html
@@ps200306 I'm sorry, that's a great find. I'll leave my comment up so I look like a goof
@@incription , hey, don't apologise, we're all goofing our way to a better understanding... including the physicists themselves. One of _Physics Explained's_ other great videos on the Ultraviolet Catastrophe led me to a whole weekend of researching the tortuous history behind that idea. The physics books can leave you with a misleading idea that every idea arose fully formed in the mind of a genius, but the real history is always a messy case of many minds groping toward an eventual explanation. I really like that _Physics Explained_ provides a potted history as well as the science.
Very smart Isaac, capable of seeing the light in a visible way, and what it was made up of.
I just returned my lab report on water refraction and I see this, good stuff :)
Thanks!
amazing, dude!
Thanks!
very good video :)
Could you do a few videos on electromagnetism and the purpose and meaning of Maxwell's equations?
Fab. Triple rainbows often occur indistinctly, outside Alexander's ragged band :)
great video, I have a couple questions:
Why does it make a circle? And why is it not a straight line of red, blue, etc across the sky at particular angles?
Excelent !!!
I have never noticed the difference in intensity in the region above and below the rainbow before, until after watching this video. How have I never noticed it before in my life?
Wow..great video...you definitely deserve the pot of gold at the end of the rainbow!
Whats the frequency of invisible light (em radiation) that emerges exactly halfway between the primary and secondary rainbows, and does this frequency carry any significance? Great video, thank you!
Hi! Excellent explanation. However, I have a little doubt. Which is the difference between the frequency and the speed of light?
very very nice
Thanks man
Thank you
Very nice
Thanks!
Understanding only enhances the beauty.
Literally mind blown, never thought this way, love from Pakistan
I've watched most of the videos now and I think they are impressive in explaining in laymans terms some really complicate sh^H^H stuff. The delivery is good, but the varying volume distracting, could the audio be normalised? Oh, and please, please, keep up the good work!
beautiful :)
Hey, could you please explain the calculus part a bit better? How does that expression at 8:40 come up? I haven't taken calculus yet but I'm curious to know
UA-cam doesn't let me post a link. Do an internet search for "The Calculus of Rainbows" by Jesse Amundsen.
Here is a question for you, since the angle of incidence depends on part of the circle it hits on, how do we account for the displacement
The diagram at 5:00 shows that. Since all positions are fixed (the sun, the idealized droplet and observer), there's only one path that will make it all the way from the sun to your eye, where the incoming and outgoing beta angles are equal. And since beta is treated as a variable, it can take on any value in the range [0,90] degrees (if you want [-90,0] just flip the diagram.. its symmetric along that axis).
And of course you can extend the argument to a perfectly spherical idealized droplet in 3D by just slicing along the plane that contains the sun, droplet and yourself since light rays can be treated as one-dimensional beams in the context of classical mechanics (until suddenly they can't.. and then you need quantum mechanics to sort the mess out but that's well beyond necessity for understanding "simple" reflection and refraction).
a little advanced for me lol but still enjoyable and well-explained, if only I could focus more and had a more basic understanding first
If the speed of light really is constant then we'd never see a rainbow at all, would we? If it can't be slowed down [or sped up] then the various frequencies could never be separated from each other. That's what I'm getting from this video. My first question was "but how can light 'slow down' if it is a constant?"
Thanks for taking the time to leave a comment. As you correctly say, the speed of light in a vacuum is constant. What causes the light to 'slow down' is actually due to the interaction between the light and the electrons inside the water. For a fantastic explanation of what is really going on, I would suggest watching this old (but classic) video: ua-cam.com/video/R8nRfs7JCOI/v-deo.html
@@PhysicsExplainedVideos Cheers :) I like those older videos.
@@alflud Yeah, me too! They don't make them like that any more..
Reminds me of those Open University videos I used to watch avidly on the BBC as a kid. It then took me another 50 years to get a physics degree ;-)
Reminds me of this bestseller popular science book called "Unweaving the rainbow" by british intellectual and evolutionary biologist professor Richard Dawkins
Hi! Thanks for posting these interesting videos. I hope you not offended by my asking what your background is. The material you present is beyond my current level of understanding, hence I can't determine if what your teaching is incomplete and would appreciate to know what your credentials are. I hope you agree that this is a reasonable question and understand that I'm not 'trolling' in anyway by asking. Thanks in advance
Not at all. I have a PhD in theoretical Physics
OMG! Now I know what video to refer then kids are asking what the rainbow is 🌈
Came here as a pink floyd fan
Came out knowing about snells law and refraction, and still a pink floyd fan
rain drops or other suitable water aerosol drops are not circles, nor spheres, so dont get hung up on specific angles being realistic. it does though show some of the beauty of science.
How did they get white light back then? Is sunlight white?
Can you please make a video on tides.. I never understood why high tides appear *twice* a day during new moon... Even though both the objects (sun and moon) are in the same side...
Think of the whole earth (along with oceans) being stretched out into a rugby ball (or American football) shape. There's a bulge in the oceans at the sub-lunar point owing to them being closer to the Moon. But there's also a bulge on the far side of the Earth owing to them being further away and "left behind". That's the essence of a tidal force: it's the result of the variation in the gravitational acceleration with distance. Each point on the Earth then has to rotate through _two_ tidal bulges in the course of a daily rotation. Bonus trivia point: the tidal friction caused by ploughing through those bulges dissipates about 4 terawatts of power.
@@ps200306 i always thought earth and moon like a magnets (that can only attract, not repel) water like liquid metal.. as earth is rigid moon's attraction cannot deform it, but it can deform water.... with this mental picture, i always end up picturing water bulge towards moon, water bulging on the other side of the earth appears as if it bulged away from moon.......
may be we shouldn't draw parallels between gravity and magnetism....
@@santhoshwagle9857 , there's no repulsion. The water on both sides of the Earth -- and the Earth itself -- is deflected toward the Moon. It's just that the further you get from the Moon, the less the deflection. So the overall effect is to elongate both oceans and Earth along a line in the direction of the Moon. The Earth is certainly more rigid than the oceans, but not entirely so. It bulges some tens of centimetres toward the moon. That's called a body tide. And of course, the Moon also elongates toward the Earth in a reciprocal way. Because the Moon is so much less massive than Earth, the friction of that tide has a correspondingly greater braking effect on the Moon. That's why the Moon's rotation has been slowed down over the eons to where it is always pointing the same face at the Earth.
Try searching for "gravity two tides per day" on youtube. There are lots of explanations, though here's a simple one that's just a hundred seconds long: ua-cam.com/video/c4b5h0Voow0/v-deo.html
Every extended object that feels a gravitational attraction also feels a tidal force, owing to one part of it being closer to the gravitating body than the other. If you jumped out of an aircraft feet first there would be a very slight tidal elongation of your body, owing to your feet being closer to the ground than your head. If you did that near a black hole, the greater gravitational gradient would stretch you out like a piece of spaghetti. Comets that come close to the Sun are often torn apart by the tidal gradient, because they are generally not very rigidly stuck together. If you Google _Comet Shoemaker-Levy 9_ you will find pictures of it being tidally disrupted by the gravity of Jupiter in 1993. The "string of pearls" is a graphic image of that comet being pulled into many fragments before it eventually crashes into the giant planet.
@@ps200306 thanks a lot... Earth moving towards moon (in the video link) confused me always.. They have used similar explanation in other videos too... However, i kind of understood it now. I understand the deformation looks like a rugby ball because of gradient... Water deforms more compared to earth. So, If i imagine less-deformed earth-ball is inside a more-deformed water-ball, there it is, bulge o on the other side...
Thanks a lot for giving your time and putting efforts to explaining it to me...
@@santhoshwagle9857 That's it!
Mathematical 🤯‼️
Neil deGrasse Tyson inspired me to know about it but you, you explained it way better. Thanks
Somewhere over the rainbow... you'll see it's dark, somewhere over the rainbow... you'll see another one 🌈
This is such brilliance! Why on earth aren’t we examined on these kinds of things in school, rather than doing 10000 iterations of Young’s double slit experiment…
I was taught thin in school. I just forgot it again.
@@tedzards509 your curriculum is better than mine then thats for sure
your voice seems so familiar but I don't know where I've heard it before
Something that's always confused me about optics. How is the speed of light different in different material, and not a constant?
What we refer to as the constant speed of light is its speed in a vacuum. In other media it's always slower, though in air it's only slower by about three hundredths of a percent.
Absolutely prophetic description of rainbows!.. one important thing I feel you missed though is a detailed explanation as to why it's shaped like a bow. 😢
@@kirkhamandy I'd just have liked to see more detail about it in the video.
Given the deapth he went into I kinda feel somewhat cheated out of the 'bow' in rainbow with only that brief description.
I should probably add, though admittedly not to the degree given in the video, I do know how rainbows work.