Young's double slit introduction | Light waves | Physics | Khan Academy

We can see interference in action if we shine laser light through two slits onto a screen. Created by David SantoPietro.
Watch the next lesson: www.khanacadem...
Missed the previous lesson? www.khanacadem...
Physics on Khan Academy: Physics is the study of the basic principles that govern the physical world around us. We'll start by looking at motion itself. Then, we'll learn about forces, momentum, energy, and other concepts in lots of different physical situations. To get the most out of physics, you'll need a solid understanding of algebra and a basic understanding of trigonometry.
About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.
For free. For everyone. Forever. #YouCanLearnAnything
Subscribe to Khan Academy’s Physics channel: / channel
Subscribe to Khan Academy: www.youtube.co...

[@ThatDudeEddiee0]

I spent 1 hour in lecture and 1 hour in lab and was so confused as to understanding the constructive/destructive interference, the first minute at 40 seconds answered just that. BIG THANKS.

[@tamilachirajeshwari701]

Can u tell me definition of constructive nd destructive interference...🙄

[@IdunRedstone]

@@tamilachirajeshwari701 When waves of same kind in cross they combine to make one wave at that point. Like if a high water wave went into another higher one it would be higher at the point they cross because the water is being lifted up by both. Constructive is when the waves add together to make a bigger wave. [aka when they cross you add amplitude together]. However if one wave was in the other direction (negative) to the other (positive), if they were at same height (amplitude) but in those opposite directions they cancel out so there is effectively no wave at that point. That's why it's destructive. Constructive and destructive usually mean where the waves are either crossing at max height in same direction (constructive) to make new one double the height, or they are same but opposite direction so completely cancel (destructive).

[@KibyNykraft]

Everyone seems confused... Why is there no interference pattern on the first wall? How do we know the photons pass gently uniformly through the next wall slits in the same manner as through the first? Let's follow the classical mechanics here of early Einstein and of the the classical physics, assuming that the photons are discrete pieces of matter : Once they enter through the first slit from the candle or lamp, there is a second wall with another slit. It is only needed a small discrepancy from the light path to create an interference pattern on the wall number 2. What the case was in Young's early experiments inspired by Huygens who of course understood that there had to be an interference pattern, was just that he assumed that photon rays would pass uniformly through all slits. But that we don't know just out of nothing; it only takes a small variation of the light path to hit the sides of the slit in the next wall, meaning there will be small pattern of interference. Some of the photons would reflect from off the back of the first wall, already having a changed path while or if going through slit 2. And so forth and so forth. Aggregated with the already discrepant variation from the main ray. Thus it has to be a wider and wider pattern of interference.

[@muhammadtouhid998]

first time in my life, i have realized what the circular form of wave representation means, all after passing everything, huh

[@sahilyadav3783]

xD

[@akshayjagtap9338]

Exactly bro

[@nisha1180]

True

[@CorisWorld404]

Beyond incredible instructor!! He not only explains the right way but also shows you common misconceptions to avoid.

[@johnparks6936]

I went through so many videos... And this one finally did it for me!! Thank you so much. Here's what I couldn't understand: why were they showing waves as propagating lines when, in reality, they were like the sine and cosine waves with peaks and troughs? This videos answered that question and even explained where they would interfere constructively and where deconstructively, Beautifully explained!

[@MrWolfchamp-xi3cu]

Didn't work for me. Still don't know what destructive interference is. Can't even find any real life examples of it. Just never see it happen. Waves don't cancel, PERIOD. If i turn on two flashlights i just get more light. If i turn on two radios i just get more sound. NOTHING EVER gets CANCELLED!!!!!

[@OmriToren]

you're doing it wrong! you need one source of light (1 flashlight, radio, sun,...) and a screen with 2 slits on it (hence the name Double Slit experiment!) if you display that light onto a blank screen you'll see interference patterns! this wikipedia picture shows it animated upload.wikimedia.org/wikipedia/commons/3/33/Doubleslit3Dspectrum.gif -- if you don't understand the physics of it, look at the philosophy behind it! i find that easier to understand!

[@MrWolfchamp-xi3cu]

The interference is those blue dots on in the green of the pic right? plus what is the philosophy behind this?

[@OmriToren]

yes! the blue would be the perfectly destructive interference (two troughs) the yellow would be the interference of one peak and one trough (+1 + (-1) = 0) and the green would be the positive peaks of light! the philosophy behind this experiment is thomas young trying to prove that light is a wave based on his experimental results. his argument is as follows: if my theory is true (A), then when i set up my experiment i will see the results that I expect (B). he does see the results of (B), therefore (A) must be true! this is a philosophical fallacy that results in his theory being confirmed (not proven) and is called affirming the consequent

[@MrWolfchamp-xi3cu]

One peak and one trough? No idea what that means. If the blue is the destructive then that means that yellow is constructive right since its brighter that green and blue?

[@AlonePlaying]

Dude, i'm from Brazil and I'm really thankful for this video. I wasn't understanding a bit of what my college's teacher was saying, you'll save my exercises. Keep doing a great job!

[@annearts5]

U learn that in college?? We have this is 12th grade in India.

[@amartyachoudhury8991]

Beautiful explanation.... especially that part where you explain how the wavefronts from the two slits interfere constructively or destructively; and finally on the screen... very helpful; thanks a lot

[@Silly825]

This gonna save me

[@TheGatoroberto]

Thanks ,good video and made very clear ... probably the easiest and most understandable explanation that I have ever found about this experiment

[@DeuceBoots]

"How 'bout the destructive points?...shoooot, you know how to do that. These are gonna be the half wavelengths." Love it. Thanks again Khan.

[@mugdhorozario4785]

Sir , The explanation enhanced my understanding. If I didnt watch this video , I would have lived under a rock with thousands of confusions So sir, I would like to thank you and would encourage you to keep up the good work for us , students.

[@fluffzxx9615]

Sar, full support sar

[@ihaveagoal4665]

@@fluffzxx9615 wow how funny, what a subtle racist remark to a student who is just appreciating a teacher for teaching him a concept

[@fluffzxx9615]

@@ihaveagoal4665 seethe harder

[@delusionalplatonist6077]

@@fluffzxx9615 you're sooooo funny bro 🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣

[@ishantripathi9707]

Oh boy! Oh boy! Oh boy! Man you explained the concepts so clearly and simply. Hats off!

[@aishwaryagorti8412]

This really helped me to understand what actually happens in the experiment... This was so helpful. Thanx a lot

[@sheriff5109]

Just take a minute and praise how satisfying the drawing on 4:32 is. Thank you sir.

[@KashafNaeem.]

Thanks this was first video i saw in this chanel and was good not boring

[@benisman]

This has been really helpful for my A-Level studies, thank you so much. I finally understood how to implement the constructive and destructive interference pattern formula w=λD/s

[@raghavpathania016]

Best of luck for tomorrow hueheuheu

[@MJ-hq1ie]

Raghav Pathania thanks bro

[@FelisChow]

Thanks for the lecture. Got me to viusalize the phenomenon .

[@josephgeraci7039]

Every time I think about this concept, it blows my mind that this is how the real world works around us

[@ydkathy5771]

ur ten minutes have covered the content that my teacher spent classes talking about with clearer explanation. Thanks a lot :)

[@maazali9456]

seriously i just understand the whole concept thank you very much.GOD bless you

[@majsterektv7528]

I just relized my teacher is useless as I always heave to learn from the internet

[@96mohormukherjee56]

Hahahaha same @majsterektv

[@e0413836]

Not sure it's the teacher's fault - realized and have! Oh there is only so much that can be built from the basic lego kit.

[@praharshsingh2095]

i dont even call my teacher a teacher

[@cnu9948]

Its your fault first did you ask the teacher or not

[@litinggoh1169]

​@@cnu9948 Maybe he asked his teacher, but his teacher doesn't even know how to explain / explain in a way that's to difficult to understand / repeat the same thing that's mentioned in the textbook. Because that's what my teacher does. KZbin is much better than some of my teachers to be honest.

[@barbros2023]

Already 2 mins in and I've learnt more than weeks of school. This teacher also doesn't sound boring and monotone. 10/10

[@melynx1159]

This helped me trillions! I learnt in roughly 10 minutes what I struggled to understand in hours of lectures. Thank you so much! ❤

[@yoanch0]

Bro, you have no idea how much this video helped me understand those things

[@geniusm3521]

The person, who understands best, explains best! perfect lecture about double slit experience. thank you

[@mannykhan7752]

I love this guys " tough love" approach to reaching. Would love him to explain human conception.

[@Telest0]

I wish I had a teacher like him...

[@sarmad1645]

this is so good im speechless!

[@johntindell9591]

i never had an intuitive understanding until i watched this video. The impact you are having on the world is deeply profound.

[@hashirkhattak9180]

You are the wizard of physics... Damn bro wow... Such an inspiration you are... 🔥... Lots of respect Love you

[@muhammadabdullahae2480]

Brilliant superb I could not understand it from many teachers but this let me understood

[@_boss_baby_]

Awosome video, Sir can you please make a video on plane wave and circular wave with diagram ,or if possible with some simulation

[@STICKSANDSTONED]

Wouldn't the properties of the slit distort the wave? WSZ

[@Hazel_61]

I don't know y all teachers take same amount of effort n passion to teach. Hats off n huge respect to all those teachers around the world who explain like this , students can understand in just 10 min rather than learning in 1hr .n it's just free.respect to this teacher n channel for helping us n making a difference. Thanks👍✌🇵🇰

[@savewater2840]

It's greatly explained. Thanks for this video

[@bettercallbhanu]

Best lecture on YDSE on YT. Thank you sir :)

[@bardotons]

thank you for speaking quickly and getting to the point!!!! great video.

[@nicotean8376]

anyone in 2020? 🙋‍♂️🙋‍♀️

[@keme_004]

2024😂✊🏻

[@HM-rc7nn]

A great explanation, for which I was looking for!! Thanks for such videos:)

[@made_in_Khaos]

Relearning this after half a decade, amazing video!

[@IsrarKhan-kb9hs]

Really helpful Jazakallah Sir👌

[@VG__]

8:20 thankyou for this clarity

[@devyanipalkar]

if you shake your head from left to right rapidly. the constructor points form a straight line to the bright spots!

[@ophiolatreia93]

I tried it and now I have a headache

[@somnathganapa5789]

Thank you for explaining the shape of the light waves before it enters the two slits! My textbook completely ignored how strange it looked!

[@shreyasmiliger1751]

I am from India and I love this Please keep continuing this...

[@christianpungo5210]

Now that all my college classes are virtual I can finally say (with evidence) youtube is just as good, or better than some teachers. Watching these instead of my prerecorded lectures from now on.

[@rakinhasan3833]

I couldn’t understand this experiment... But now I can understand this.. Thanks khan Academy 🖤

[@sreyasthejas4715]

thank u soo much for the video . one of the very best videos on interference out there.

[@huanganan700]

Thanks so much for perfectly visualizing the process of light diffraction. Always love Khan Academy😄

[@vamshikrishna323]

Iam a bit confused about this experiment..but with this vid my confusions just got rid off....thank u very much 😃 for uploading this video...

[@sharmass3756]

super explanation I got all my doubts cleared excellent

[@effectbest7532]

Thanks man this cleared all my doubts ....Well explained

[@LawGTSenpaiLaw]

My teacher’s name: Leci Things she’s good at: being useless and bragging thanks lol I’ve a test in 20 mins and I finally understand the experiment

[@beigeboi_7714]

Poor Leci :(

[@premedmelody]

This just blew my mind

[@rishimalhotra7331]

8:36 how did you know that i made the msitake of thinking that....😂😂. great video thanks!

[@YAC270]

I still didnt understand it? Can u elaborate?

[@unknown-ku4ri]

oh its so easy before watching this video every time i thought about this topic my mind was liking bursting Thank you so much.

[@adamdangelo7644]

You saved my life. Thanks

[@adthya9209]

best explanation of YDSE ever. period.

[@VG__]

I request you to change your cursor so it's visible where you're pointing while explaining. Thankyou for a crisp explanation.

[@harshgaonkar5834]

Is intensity same for all the fringes in double slit expt.?

[@munshaatatiq1435]

Can you please add subtitles in your next videos? Thanks in advance

[@qiuk5988]

Thank god, someone is able to explain this properly since my prof is hella horrible

[@beyondemotionsvibe2408]

Bro, thank GOODNESS YOU EXIST!

[@HoussamBenhallam]

You made my day ! Thank's a lot

[@k95channel]

thanks for your helpful explanation!

[@GurpreetKaur-rw2ts]

Superb sir pls make more videos related to physics

[@DinaHelmy]

Thank you!

[@bluecloud3059]

Thank you so much. The best video for explaining Young's double slit experiment.

[@virtualgirl7697]

Now its very easy to visualise and reason.thanks😊

[@roboticsresources9680]

such an excellent video..the concept is explained so clearly....best for K-12 students

[@sharmass3756]

yes

[@PeaceboneGotFound]

THANK YOU for explaining this so well!!!

[@Inovb]

That's explained very well thank you.

[@mgpvii]

I saw a video on this from Neil DeGrassi which points out the most interesting, incredible, unexplainable part of this as that if someone observed/watched the experiment the pattern would just be two slits on the opposite wall. If no one observed it, then it would be as explained in this video. It happens every time and no one can explain it. Observing changes reality.

[@zahrashahabinezhad]

Absolutely fantastic videos on this topic. I finally understand this. Thank you!

[@guillaume6373]

amazing!! thank you very much

[@RealEverythingComputers]

Thank you so much! This video was very helpful

[@Rubi747HVY]

Thanks for clarifying so well.

[@mathewjoseph738]

this vedio is very effective......

[@-fish-3316]

Very clear explanation! Thank you!

[@niveyoga3242]

Best explanation I've ever heard!

[@pratiksaha2592]

Thank god Sal didn't taught this topic or else I don't think I could have understood so well..............Thank you so much Khan Academy for uploading this video.

[@bhruseantv3461]

it was really helpful...thank u for such a great vedio...

[@095-anamaykashyap2]

well explained ... definetly helpful for boards and jee

[@okhan5087]

Wonderful explanation

[@marwaebrahiem7485]

Thanks allot for the exaplenation

[@Medusaogre]

Best explanation I've seen.

[@Aliens797]

amazing explanation! thank you for the review!

[@32kirby32]

Perfectly done

[@annearts5]

4:12 he didn't have to join all the dots and make a line which makes the bright spot, if y'all noticed optical illusion does it for us! This is insane

[@STICKSANDSTONED]

Does the double slit equation account for the thickness of the wall? Slit distance, slit width, slit proportion...can you adjust these to find phase? And how does it look visually.

[@wasteyourtime4961]

God bless khan academy

[@lordepixz6364]

This video was really helpful! thank you

[@001khokhar]

Excellent explanation of a very conceptual topic

[@kiranrq9387]

Wow!!!! You are a hero! I just woke up and stressed about how these wave interfere, but you made it like a piece of cake 😊 thank you very much. I still have a question about diffraction. Say the slit gap is exactly same as one wavelength of that particular length. After it is diffracted it spreads out, so does that mean that same wave’s wavelength increases as it moves forward ? And the same amount of waves go through that slit each time? As I have seen water pressure increases through holes. Does pressure make the amount of water flow increase too? Or again it is just as it spreads out it’s wavelength increases? Pleaseeeeeeeee help

[@biogasmsr3321]

this is a question "young double _slit experiment is performed with 589 nm light and a distance of 2 m between the slits and the screen . the tenth interference minimum is observed 7.26 mm from the central maximum. determine the spacing of the slits .

[@TheAnonymousUchiha]

Just asking but is the answer approximately 1.6 mm?

[@madmythic123]

Isn't the intensity of the bright spots same in the YDS experiment?

[@rakshanabala5062]

Well....... i have heard something like that too.. But i think it is the fringe width that remains the same and not intensity. The width of the primary maxima is the same as all the other secondary ones. Because the intensity has to vary at points farther away from the slits . While in diffraction the bright spot in the middle is the largest and the size goes on decreasing from that.

[@bestmartialartsfightingsce9813]

Thank you ❤ you are life saver

[@akashneelsaha8300]

This is so amazing

[@gboyawesome1159]

Thank you so much I understand it now

[@MysticMD]

Wow i understand now. Thanks !