# Newton’s Prism Experiment

(mechanical sound effects) – [Voiceover] In this video,
we’re going to look at the relationship between
white light and color by recreating a portion of
Newton’s prism experiment, as presented in a letter to
the Royal Society in 1671. But first, a little bit of background. At the time of his experiment, the prevailing theory was that white light was a color of light,
and that other colors could be created by modifying
the white light, somehow. For instance, this red piece of plastic would be described as
changing this white light into red light. They also had knowledge
about how light behaved at the boundary between two materials. For instance, a planar boundary, they knew that the ratio
of the sine of the angle on each side of the boundary was fixed for a given set of materials. We now know this was
a form of Snell’s Law, where the ratio of the sines of the angles is equal to the inverse ratio of the refractive indices of the materials, where the refractive index of the material is related to how fast
light propagates through it. This expression allows us to predict what’ll happen in that planar boundary as we change the angle of instance. It also allows us to deal
with more complicated shapes, like this triangular prism. It’s just a matter of geometry and keeping track of the angles. Newton was working on
designing lenses for telescopes when he decided to
investigate the phenomenon of prismatic colors. Those are the colors that occur when you pass white light through a prism. You obtain a triangular prism, and you pass some white light through it, and he saw a rainbow,
just like he expected. Then he noticed something, in the direction that
the colors were spread, the pattern was much
wider than it should be based on the system geometry if light obeyed this fixed sine ratio law. He did some experiments. He separated out individual
colors in the spectrum and passed them through additional prisms, but what he came to realize
was that all the colors in this spectrum are
their own form of light, and they all experience a
different refractive index upon travelling through these prisms. This led him to the conclusion that the white light entering the prism wasn’t really white, it was a combination of all these different colors. And that all the prism was doing was separating them on an angle by this varying refractive index. This was an interesting conclusion, but doesn’t really prove what’s happening because we’re still relying on this prism to make these colors. What we really need is an experiment where we can form these
colors from white light without a prism, and at
the end of his paper, Newton suggests just such an experiment. You start with the same
system you had before and then you place a lens in the system. We start with out screen close to the lens and we see the same
spectrum we saw before. Here is the light passing through the lens and up above it, we see the light that’s sort of skipping the top of the lens. As we move our screen away, the colors begin to
overlap until at one point, we see a band of white light. As we continue to move
the screen further away, we see the same spectrum
that we started with, but with the colors now reversed. As we move the screen in this experiment, there’s nothing to cause
this change of color that we’re observing. The only thing that’s changing is the overlap of the colors. We can conclude that when we
perceive this white light, what we’re really seeing is a whole bunch of colors added together. It turns out that you don’t actually need all of these colors to trick
your eyes into seeing white. If you’re watching this on a TV screen or a computer screen at home, what you’re seeing as white is actually a combination of red, blue, and green. But for our purposes, we’re seeing the sum of all the colors in the input spectrum. Okay, that’s pretty neat. We start off with white light, we form a spectrum of color, and then we use a lens to
combine it back into white light. But it only really combines
it into white light at one spot, if we go
further away from the lens and closer to the lens, it’s
still clearly a spectrum. Is there a way to combine this white light so that we get a beam of white light sort of like we had at the input? It turns out, the answer is “Yes.” But it’s a little more
complicated than you would expect. A lot of books draw this system, where we start with out original prism, then we put a second one
in, something like this. To our eyes, this looks like it’s working, but it’s not, really. All that’s really happening is, the white hasn’t had
enough time to spread, so it looks like it’s white, but if you add a very
sensitive instrument, you’d be able to tell
that there’s a change in color across this. You can see it more clearly by eye if we place this prism further down. Over here, it’s clear that there’s a change in color across
the width of the beam. If you really want to
make a beam of white light from this colored spectrum, you can follow the method
outlined in Newton’s Optics. This comes from his last
that we had before. Then you add a lens to the system, and you want this length to be roughly twice the focal length of the lens. At some distance away from
the lens, open another prism. And this distance, again, should be roughly twice the focal length. We adjust the prism, and what see is a reasonable
approximation of white light. You really should build this system with a much larger focal-length lens, and should build a much wider system to get a really good separation between these colors, here. And a very clear white beam at the output. But for this video, this’ll work. Thank you for watching. I hope you found this
material interesting. If you’d like to learn more about Newton’s optics experiments, I’d recommend two resources online. One is the Project Gutenberg, where you can find a copy
of Newton’s book, “Optics”. The other is the Newton Project, where you can find a copy
of most of Newton’s papers.

## 100 thoughts on “Newton’s Prism Experiment”

1. celio gouvea says:

I still don't understand why the triangle shape (section of the prism) separate the colors and the rectangle or square don't, we can see only a refraction? In another words, how the photon knows the glass has different shapes and decide to take different directions?﻿

2. Daniel Z says:

Where can I get a prism like that?

3. Glamalicious says:

why am I even here?

4. Abidin Berk says:

That's pretty cool, best desk made video I ever seen about Newton's Prism experiment. (: Go ahead.

5. Willie Pep says:

6. 신혜준 says:

Why does the light become white when the light passes through the second prism? Can anyone tell me why?

7. Javinshki says:

Cool!

8. 510suess says:

is there any artificial source of white light that you know of that can be used to accomplish this experiment well? If so, what is it, and how would you set it up? I have not found a good way to adequately collimate light from an incandescent source. Thank you.

9. Tarwin El físico says:

Podrías hacerlos con láser newton prisma.

10. Sn.Balcı says:

Müfredatı sikiyim amk yansımalark öğrettiler bunu gördüm aklıma gelmedi acaba 1 sene geçti üstünden ondan mı ki ??

11. international Remixes says:

wow!!!! u know my eyebrows were raised

12. Pranav R says:

when the screen is moved is it because of the lens's focus length is the light again appears white or is it because of some other reason?

13. املى المعرفة says:

wonderful

14. The Beats says:

i was always wishing to see a actual spectrum from a prism

15. Dinesh Sahu says:

excellent

I to everyone who cant figure out how he got a beam of white light. Its clearly sunlight. its the best light for this and the beam can be created by a couple pieces of cardboard over your window. or just barley crack your curtains if you have dark enough curtains to block most of the light.

17. Oğuzhan Yılmaz says:

Aynı şekilde telefon el feneriyle öğrencilerine anlatmaya calışan bizim hocayı gördünüz mü işte eğitim farkı

18. Zhip_ 2005 says:

Interesting…

19. Zhip_ 2005 says:

😐

20. Sergi Jiménez says:

Yo entender…

21. Gaimz says:

Fascinating

22. Anitha Reddy says:

we get a great imagination when we watch and we understand

23. Raghav Rajpoot RR says:

Thanks sir

24. The Roblox Master says:

im only in grade 4 and i understated EVERYTHING SO EASY OMG

25. xd Aspéctz says:

26. K R Raju says:

Fantastic

Nice

28. Albeit_Jordan says:

Lovely video!

29. ali ali says:

Can we recollect the white light again from the seven colours?

30. Jay Andrew says:

So what would the color pattern project with a 2 dimensional square or round slit of white light? In looking at the sunlight projecting a curious pattern through the square shaped beveled glass on my front door this morning. Top down-violet, blue, white(center of glass is flat,1/2" beveled edges, 1/4" pane)yellow,red. Left to right looking with the light, red, yellow, white, blue, violet. WHY is red or violet not the initial edge color of the symetrical square beveled glass? …….with respective colors following as the square beveled glass thickens towards the middle? The glass is symetrical BUT the refraction is not. Anyone? Thank you

31. Brandon Pea says:

All I can now is think of Necrozma

32. Flávio Peloia says:

Ok now how to convert red light in matter?

33. Elvis Menezes says:

Can we use red lasers?

34. Sage 1123 says:

This is some screwed up crap. 2:00 it talks about how white light is made of 2 lights, because half work one way, and the other half work another. And solid proof that white light has 2 lights, like the sun as in one light and the moon as the second light and both above your heads. No proof what so ever to show how red, orange and yellow make white, just one end of the color spectrum.

35. NEETA DESHMUKH says:

At 1.48
Why does the refracted ray(before the screen is kept) is still white?why cant we see the VIBGYOR in mid air also?

36. Sajeel Munawar says:

pk maru dang SE prism rakneich nai aata

37. Make Me Scientific says:

Gr8 video Thanks #makemescientific

38. Jeffery Doud says:

Thank you!

39. hemal bosamiya says:

Fuck

40. Mysticroach says:

2:45 Rainbow Dick!

41. MIG UEL says:

We live under a dome🌈earth is flat

42. SAND says:

My friend my question is why rainbow appears in sky and our normal prism don't show that light in air??

43. Hamza Zaki says:

LOOOOL THEY MADE THE DARK SIDE OF THE MOON COVER A REAL THING

44. M.Servet Tümkaya says:

What is ‘Tested, determined, examined’ here ¿

45. Molotov With Lux says:

#prismairwaves

46. Imrankhan Nagori says:

Nice

47. Gustavodlp says:

It would be cool if he blew smoke onto the beam to see the smoke illuminated in different colors and showing the light path as the colors separate

48. Cripple kid 090 says:

Great video

49. Humphrey the Elephant says:

Breathe, breathe in the air

50. Santosh Singh says:

I make the newton disc in my school exhibition and I am stand first in my class

51. Jyoti Rungta says:

Can we use torch light as source of light … Pls tell I have presentation in school .. pls

52. leo kogler says:

I think it is not an experiment, it is an evidence for different colours bundled into white.

53. leo kogler says:

Every colour has a different wave length, but bundled it only has one, the white one. – am I right in thinking this way ? Is there a theorem for that phenomen ? – please let me know. 😉

54. leo kogler says:

Perfect explanation, thank you.

55. priyanshu Raj says:

What is requried angle for formation of rain bow

56. School TV says:

very nice video

57. Fozi Nasir says:

That was very interesting and gas what I have the story of Isaac Newton making rainbows.

58. white devil says:

💩

59. white devil says:

sorry I have to send

60. white devil says:

😄

61. james swampy says:

it it possible to bend light 90deg without causing the light spectrum or rainbow affect

62. Rehmat Elahi says:

WHATS THE REASON BEHIND THIS EXPERIMENT RATHER BEING INTERESTING??? JUST ASKING

63. muneeb rider says:

Good

64. James Bogucheski says:

The same effect happens when light hits dense smoke at a certain angle.

Very nice

66. КАТЯ ЗЕФИРКА# says:

2019?

67. The IQ Zone 2 says:

You explained the concepts very fluently and the experiment is of great help to me. Thanks Sir.

68. big strong boss says:

nice video but those thetas are disastrously ugly

69. Rahul Hoque says:

Nice practical of prism

70. Mohd Bilal says:

Why does the light only disperse in prism

71. Daya Shankar says:

How make own prism

72. Safa Alsaed says:

ممكن تنزل لفيديو يكون مدبلج بلعربي

73. Sushma Chandra says:

Thank u for making this video .this video help me very much 👍👌👌👍👌😊

74. CIENCIA LÓGICA says:

Trichromatic theory of light composition, not only of color. There are only three photons

75. Elmer Jones says:

Can you tell me the make of the ray box you are using? Thanks!

76. Conquerer 44 says:

Me: Learning about colors and light at school

Me: How the fuck did you know!!!!

77. Earl Pierce says:

But explanation of whhhyyyyy???

78. Food4u says:

did you notice that …why no black color init. which color of death for stars in the sky..and dark is silance of universe.. the color whic not included in the light its dark and for humans its visulaized as night or death when we close our eyes. or finally zero code color.. so zero has its own value..without dark,light cant be specialized.. dark is very special color.

79. Thoughts and Themes says:

where to find the plano convex lens used here? Help

80. ovodot says:

Thank you for the simple and concise explanation. Did you use acrylic or glass prisms and lenses?

So how many colors are there?

I saw red yellow greenish and blue (violet)

So bored 😴😴😴😴😴

83. Fatema Tuz Zohora says:

Woooowwww

84. EDUCATIVE STATUS says:

How did u focus the ray of light so narrow line ..?

85. Michael Melling says:

Racism.

86. Akhil Garg says:

It's not white light dumbo, we actually perceive it as colorless light , this means light has no color and infinite colors at the same time. This means, 0=∞, we are in an illusion guys.

87. seyam shah says:

👌

88. perentee77 says:

So if you had torches that were the colours of the spectrum and shone them all at one spot you would see a white light?

89. Aleksandr Makhno Artamonov says:

I wonder if the light that the Moon reflects has the same spectrum with white and yellow shine than the Sun?

90. Davonkey2life _ says:

What this guys says is what I don’t understand

91. Davonkey2life _ says:

Now I get it

92. Gleb Tokarev says:

Don't be afraid to care

93. Neverknown says:

Wonderful 👍👏

94. matt waters says:

Maybe the wave frequentie of the white light gets disturbed by the prism and goes on in different waves with every wave an other frequency and that makes us see the rainbow, eventualy the waves meet eachother and form white ligt again only to be disturbed again and move on with again the different waves and frequenties

Just a thougt

95. Md Farookh says:

Need 1k more views to hit 1M views. Congratulations sir..

96. Animeetchi says:

Are there other materials other that glass that can be uses as a prism? If so Are the molecular arrangements similar?

97. Panas G says:

Interesting…