What causes a rainbow

[@DrPhysicsA]

Well done. You are the first to have spotted that. I had read off the wrong values - the ones I quote relate to the angles of incidence. Yes the angle for red is 42.37 and that for violet is 40.65. I am very grateful to you for pointing this out and have added an annotation to correct it.

[@DrPhysicsA]

Refractive index is the ratio of the speed of light in vacuum to that in the material (in this case water). Light slows down when traveling thro water. Its frequency doesn't change but its wavelength does. So frequency and hence Energy (E=hf) are not affected by refractive index. However, the refractive index for red light is different from violet light. So if white light has a specific angle of incidence then the refracted angle for red will differ from violet - hence the spectrum of colours.

[@lomertamahon1]

Still, the best physics lectures on the internet.

[@DrPhysicsA]

Well all raindrops above the critical angle refract no light and all raindrops below the critical angle refract all colours (ie white light) so it is just those raindrops which happen to be at the correct angle to refract only some of the colours that count. The light passes thro very quickly. The continuous effect of the rainbow arises because light is passing thro all the raindrops which just happen to be at the correct angle as they fall.

[@DrPhysicsA]

Yes I have. The second bow is usually much less bright.

[@rsk75]

Brilliant, thanks for explaining in detail.

[@dongodilorica6037]

DrPhysicsA deserves more views. Thanks always for the great contents.

[@dalefmurphy]

Best explanation on KZbin!

[@ArcticAstrophysics]

Just to clarify, a rainbow is not actually a semi circle but an entire circle, only cut off by our inability to see through the horizon, and a rainbow depends entirely on your position, so if someone is standing several meters in front of you, they will see their own rainbow. So does this mean when there is a rainbow, there's essentially rainbows everywhere, but you can only see one depending on your position?

[@tracylouisepoynton]

Yes there are rainbows everywhere

[@maddman3598]

so tell me how is the raindrop magically suspended in space, or why is it not flickering from the different raindrops, because they are dropping fast and a rainbow can last a while.

[@jeffjo8732]

A wonderful explanation. With a couple of details that are not quite right. I'm not trying to point fingers, I'm trying to clarify those points. A trivial example is the use of the word "refraction." What DrPhysicsA means is "transmission," or "it crosses the boundary between the two media." "Refraction" means it changes direction during transmission. Another is the mistake he admits in another comment. 59.53° is the angle of incidence when red light emerges at the rainbow angle, which is 42.37°. But he calls this the "critical angle", which is an entirely different thing. That's where total internal reflection occurs, and it can't happen with rainbows. It is commonly used as the explanation for the bright bands, but that is wrong. So what causes the bright bands? When i=0°, the deflection angle is d=0° (that is, straight back). As i increases, d also increases, but the rate at which it does so slows down. This has the effect of making the emerging light brighter as your eye moves from the center of the cone to the edge, since a wider range of incident angles contribute to the deflected light. At i=59.53°, d stops increasing altogether, and begins to decrease. At that single point the light is, in theory at least, infinitely bright. This is a similar effect to what causes the dancing lines of sunlight on the bottom of a swimming pool or shallow lake on a sunny day. The secondary rainbow is caused by two reflections, not three. The interesting thing here is that the "cone" of light is pointed in the same direction as the original sunlight. (That is, i=0° means d2=180°.) The cone is about 130° wide, which means it wraps around the top of the sky. Red is still on the outside of the cone, but the cones is seen upside-down, with the "white" part above the bow.

[@leopardtiger1022]

Clear Clear beautiful explanation... Thank you.

[@Im-just-Stardust]

No matter how many time I heard that cow clock, im still laughing every time.

[@just_anybody]

Thank you for this. One question, if two people are at the same latitude and longitude but at different altitudes, is it possible that one will see the rainbow and another won't? Example: Person on the ground sees a rainbow. At the same time, someone in a plane 35,000' above passes directly over them looking in the same direction. Will the person in the plane see the rainbow as well or will the height difference change the angle significantly enough to make it invisible to them? Really appreciate the video, I'm not 100% confident in total understanding but you've helped me come close.

[@tracylouisepoynton]

I think no as it is also about the position of the cone and the reflection through and out of the cone . Higher up is in the dark matter spectrum so we'll see clouds and not actually notice or acknowledge dark matter. Dark matter is everywhere

[@Orangelina29]

It depends on his angle.... Maybe he will see a definite one.... A rainbow does exist only to your eyes. Depending on that definition.

[@Grinder-one]

Brilliant, thanks.

[@ambientmusic8401]

What causes a rainbow, ohh come on.. off course it's unicorn farts..

[@tracylouisepoynton]

Hahaha I need to rember this

[@yeslist]

Good thinking but doesn't the sun hit every rain drop from the same angle of its reflection?

[@jackpistone8015]

Fantastic video

[@vincentarsenault6067]

I love this vid its perfect for my project

[@shikhakashyap5591]

Love from india🇮🇳 amazingly explained

[@prasadradhika]

In the video, phi was the max angle at which light comes out. On other websites it is not 60 degrees but around 42 degrees for red light and 40 degrees for violet light. Please explain.

[@king_51556]

apply raindrops can cause light wave to bend. what other substances can cause a rainbow to form?

[@Skellborn]

Fantastic Video! I finally understood what i've alway asked myself I'd loved if you hadn't skip over why there are these maximum angles for the different colors (60° max, 59,... for red, 58,... for violet) i suppose it has to do with total refraction, meaning light can enter the droplet only at certain angles?

[@shubhrajit2117]

Best explanation!!

[@roygbiv176]

Shouldn't the whole of the space inside the rainbow be violet then instead of white?

[@unphasedablazeray56]

(At 10:48 in the video) So the the reason why we can still see the rainbow in all it's glory is because of the perseverance of the perspiring radiation of the ray wave length into water molecules creating fractal luminous (4)envelop) of a developing rainbow at the right angle of perspective?

[@zaahidapatel1362]

We learnt that in optics at uni. ... anway what I find flabergasting is how everyone contends themselves with the understanding of a rainbow at a microscopic level .... think for a sec and apply that on a macroscopic level ..... we all concentrate on the angles and the colors ..... hey don't u realise that when light passes thru a prism ...for it to be visible it has to hit /touch /bounce back on a SURFACE. Yeah ..... there is no "surface" in the sky. ..... so what plays the role of a surface and allows light to be visible ON IT ...the same way we see the split up light coming out of a prism on a wall/piece of paper / surface ...... what's the "wall" in the sky ..????? A field ? The only field pre existing on earth is the magnetic field. .... how does the magnetic field act as a surface of "display" how does it "stop" light from moving forward the way a wall does ........ remember what maxwell calculated with his equations ........when he discovered that light was an electromagnetic wave (@arvin ash his video was quite informative)... ...let that blow your iq. 😅 Can the rainbow be another manifestation of electromagntism?

[@saskoilersfan]

How rainbows appear... How the moon disappears.. Taught me how to advertise on earths atmosphere... By using a human eye as earths atmosphere.. Do other planets that rule earth drop hints?

[@thebigfoot4456]

What about the 42,4°?

[@maaan8494]

Is it because of the earths curvature that the rainbow is an arch?

[@peterb9481]

So well explained.

[@TS-vh9rs]

6 O'clock Stories THE COW😂

[@YoussefMedhatAboutaleb]

Thank you, Have you ever seen a double rainbow?

[@NaturalScienceKid]

But what causes the light to be reflected twice within the raindrop?

[@DrPhysicsA]

The surface of the raindrop so you have the usual situation where light moving between water and air will partially be reflected and partially transmitted.

[@NaturalScienceKid]

Thanks!

[@Orangelina29]

Maybe different drops temperatures! 😜 Different sizes... Different layers....

[@7jboogie]

[@muchufoo]

Thanks for the video I never knew that light can be reflected multiple times in a raindrop. Does the refractive index also determine the different outputs of wavelength and energy?

[@lebranjomes8498]

Why can a rainbow become a full circle then?

[@rajeevsharma3767]

At first point it gets refracted,at second it suffers TIR, then how it get refracted again at third point even the angle of incidence is same in second and third case

[@vincentarsenault6067]

hey dudes wats up

[@valor36az]

Great explanation would have liked to hear how the mathematics was derived

[@punkylilkid]

I like the cone thingy

[@Orangelina29]

So there must be a shadow for the rainbow!??

[@cthroo303]

I thought water absorbed every color except blue that's why oceans are blue

[@Orangelina29]

No.... Not right. Water drops doesn't absorb any colors it only reflect depending on surround.

[@Orangelina29]

Technically it is black but yet it reflects the color of the sky.... And also as well sky is black but because of the atmosphere meroring of the morning as the cpace is dark..... Also reflect the color of the atmosphere leyers...

[@internationalremixes6440]

hey the cow clock again!!

[@Orangelina29]

❤️

[@2fungirlz]

Interesting tyy

[@nickrobertson5294]

NEEEEERRRRDDDDSSS

[@tracylouisepoynton]

A raindrop isn't sphere it's a drop. Didn't this change everything matamaticaly

[@Orangelina29]

Haah

[@Orangelina29]

Well technically it is not a raindrop it is water stuck in the atmosphere.... So it is certainly a spherical in shape!

[@saskoilersfan]

One day you'll figure out how I solved how to advertise on earths attmosphere...

[@rodericksibelius8472]

I think You watched the MIT Lecture of Professor WALTER LEWIN... hahahaha...

[@jeffreydemeulemeester1951]

That cow hahaha

[@martinhorak8475]

This is totally incorrect explanation

[@swampwiz]

Although there is a lot that is accurate here, there is some that is not accurate.