Diffraction grating | Light waves | Physics | Khan Academy

[@bboy14]

Khan academy needs to keep you on board, your explanations and commentary style is a treat!

[@Cooltaha]

such a clear and concise voice

[@fluffzxx9615]

I don’t get why in the normal double slit it would be smudgy in the first place, why?

[@albertvandrejer5003]

@@fluffzxx9615 because for a large numer of slits, the condition for constructive interference of all the superimposed waves is only given at very specific positions. For a double slit what you see is just the interference pattern of two waves, which will have areas of constructive interference, destructive interference and everything in between.

[@williamstephenjones3863]

Agreed

[@SAKA701]

Grate video, must say.

[@chrisbuckle6930]

Aly Azeemi great*

[@SAKA701]

Chris Buckle Ik dude, it was a pun :p diffraction grate-ing. YES IM THE LORD OF ALL BAD PUNS.

[@divyasingh9291]

Aly Azeemi ikr😂😂

[@SAKA701]

TOP COMMENT WOWOWOOW, FeelsGoodMan :D

[@the_golden_one4733]

Dont grate on my nerves

[@ponypony4695]

If only my teacher at university could explain this in the way you did... thanks, now it looks much more easier to understand ;)

[@LASTCHANCE-mi8zy]

says who

[@mr.j_krr_80]

10:55 "in between you'll get *darkness* " me: I know... *turns off light, sits at the corner and falls into depression*

[@yashgaikwad7516]

Mr. J_Krr_ :(

[@MJ-hq1ie]

A whole mood

[@splinter1817]

sed lyf

[@kushalchakrabarti240]

4:03 .. how about a third hole? This is where it gets interesting... LMAO

[@expectopetronum3851]

😂😂😂😂😂

[@abdallababikir4473]

Brother,😂

[@AbdulHamid-uw2oe]

Mouth..vagina...&...... The thid....

[@sarahholland5980]

you just explained a full lecture in 15 minutes, and beautifully and simply. bless you.

[@Integrelle]

2:12 "Why? Well, lets talk about why." LOL, reminded me of the GMM quote, "Lets talk about that".

[@ufo717212]

I just tried to reorganize your points in my own words as the following. At a magical spot, each light travel one wavelength further(or less) than its adjacent light. Therefore all lights results in constructive interference at this spot which is bright. At a non-magical spot, each light has a slight phase difference with its adjacent light. Since there could be hundreds of different lights from hundreds of holes, each light can always be paired with another light with a phase difference of about half wavelength. Thus each pair results in destructive interference. Overall they result in darkness at the spot.

[@kissmyussr1993]

Who are you so wise in the ways of science?

[@vandnashukla3598]

This is exactly how I tried understanding it.i took approximately half of the total number of holes and then each point in between the initial and final hole would pair up destructively with another.

[@Ahmed-vs1ui]

How does that magical spot even exist mathematically

"And in between these bright spots you will get darkness...which is grate."

[@fluffzxx9615]

I don’t get why in the normal double slit it would be smudgy in the first place, why?

[@epickirby101]

Fluffz Xx cause the waves won’t completely cancel out in between, partial destructive or constructive interference

[@zeenathunnisa3571]

Gosh!! Such an awesome and clear explanation. Jazakallah Khair.

[@Postermaestro]

This was very well explained. You guys at Khan are so good at making it easy to understand, which makes the learning process so much more fun and time-efficient!

[@cortwill4085]

OH... ME... GOSH!! IS THIS... ARE YOU... KHAN ACADEMY KIDS?!?!?!?!?!?!?!?!? I LOVE Khan Academy Kids so much! l couldn't even help myself but to get a game of you guys on my iPad! I like all the characters: Peck, Ollo, Kodi, Raya, and Sandy! But I think... Sandy's my favorite! Khan Academy Kids is all l play! Like, I literally don't want to play anything else on my iPad! CONGRATS!🎉 You get 5 stars!⭐⭐⭐⭐⭐ I wanted to give you 5 stars in the game, but it required a PIN that only Mum and Dad knew. And they won't give me permission to give you 5 stars. Here you go!:⭐⭐⭐⭐⭐

[@Lyoko-wy3si]

I barely understood the idea of diffraction grating until I watched this! Thanks for the help

[@simonhwang5624]

Right at 3:00, you say "draw a right angle", but if it's a right angle there's no way the two lines (minus the "extra part") are equal, because geometry: hypotenuse of right triangle must be longer than sides.

[@adityamathur5972]

Same bro, even I didn't get that

[@nononnomonohjghdgdshrsrhsjgd]

@@adityamathur5972 i was scrolling through the comments to find that question and some explanation

[@divyansh_kashyap2901]

​@@nononnomonohjghdgdshrsrhsjgdbecause the angle between both hypotenuse and one side is very very very small...approx 0⁰.. Cos0⁰=1=(base/hypotenuse)

[@Kolinnor]

I think he meant to draw an isoceles triangle.

[@chaosforever]

11:50 no this actually all made perfect sense, thank you!

[@4darekord]

crystal clear explanation man

[@annaszinyei]

You did such a great job explaining! So clear and easy!

[@luigiprz5319]

Hi, to keep angles, so green lines, the same, the purple lines should be parallel. We cannot approximate angles because the difference distance is much bigger than wave length. Correct me if I'm not right. It looks the same when draw is not precise but geometrically not. What if first hole will be perpendicular to bright spot and the x hole will be at the border of light point :) but you got good intentions it's the plus

[@haristufail2121]

Beautifully explained Sir.You should get a Noble prize.

[@FDGod99]

-_-"

[@FDGod99]

+Onkar Apte -_-"

[@gracepancalstatela4422]

I agree👍.

[@LogicalCod]

Nobel

[@harrisabdullah2278]

If there was a nobel prize for teaching

[@trailertrashtactics]

This guy is like a young sassy Sal Haha. Love it thank you for the videos.

[@4rthur4rmstrong]

All David’s videos on physics has been absolutely amazing!

[@oscarpalmowski9003]

best video on the internet about why diffraction gratings give discrete maxima. THANKYOU SO MUCH. I wish I cam across this video first

[@animeBHARATIYA]

The explanation is very clear, thank you

[@Aditya-f8t5z]

Thank you for making this video. 🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏🙏

[@RedBar3D]

Actually drawing them parallell seems to help understanding a whole lot

[@jinks6887]

really well explained thanks a lot ..love from india

[@smtusharibnesalam8688]

Its Great. Mind blowing. Top class video. Thank you very much for teaching this

[@MrRak18]

It helped me understand x- ray diffraction.. thank you.

[@workingemail1016]

Very well explained. Thank you.

[@RahulGupta-pf4yt]

Your style of teaching is remarkable.

[@alivira1558]

Never understood what the concept was before but this was like magic.. well done and thank you so very much.

[@mastersanjay7642]

Amazing explanation and content hat tip

[@sotirissarros3522]

many thanks man. it's clear that you really want to explain the subject and you do it perfectly!! well done!!

[@SohamChakraborty42069]

Beautiful explanation. One part I don't understand though. The angle theta is the angle between the perpendicular line joining the middle of the distance between the pair of slits and the screen and another line that joins the middle point and the point of interest on the screen. In diffraction grating, we are choosing different pairs of slits each time, so the middle point changes whereas the point on the screen remains fixed. How is the angle the same, then?

[@physestryshorts5214]

omg ..... no words for this lecture

[@ChanakyaVivekananda]

Mannnnnnnn This is such a good explanation!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[@BlueRangeTV]

Thanks, the Bulgarian student books don't explain this well at all! Finally understood it

[@mariamnaeem6963]

Wow!! Thank you for posting such a wonderful explanation! I was so confused that how wavelength is determined and you have cleared this concept briliantly!

[@kushalchakrabarti240]

This guy is great!

[@astroknight5]

Beautifully illustrated!

[@GoogleUser-ee8ro]

so clearly explained

[@MariaShchurova]

That;s incredible. Thank you for your work

[@MohdSameer-rx9gj]

Very very nicely explained.....!!

[@CalvinUlbricht]

very well explained video, thanks a lot, really helped me understand it better.

[@udays6170]

Beautiful explanation!

[@chrisjieyanglee5360]

thanks bro you've helped me alot!!

[@hokwanchan4142]

the video gives me a clear idea of diffraction.thanks

[@edit..x]

Super interesting ❤️

[@Cherrilady83]

God Blessed this man.. Tysm❤

[@faizanrizwan786]

so comprehensive! thank you!

[@TimeGrowing]

Hey man you just killed it's been one month on school teaching me,but I didn't understand. And you, just in 14m you make it easier than drinking water. Thank you so much.

[@wooluke7144]

Wow. Very Well Done. All Capitals Letters.

[@bithipaul6810]

Great video..sir..outstanding...

[@hoangphamcong9230]

realy clear! Love it

[@sayan_debnath]

Great explanation.. Thank you

[@jasonhng8135]

nice video about diffraction grating!

[@angikmukherjee1226]

You nailed it man!

[@kitanomarumilitoni9293]

I understood that very well. Great job sir thank u very much!

[@gracepancalstatela4422]

best explanation!!! Thanks a lot .

[@tom_something]

This is super clear, thank you. One thing I was wondering as I looked at this. Shorter wavelengths should, then, encounter these positive interference peaks at smaller angles. And I was trying to reconcile that because I know "blue light diffracts more than red light". But I looked it up, and in a diffraction grating, blue dots would be _closer_ together. I had assumed a diffraction grating would work the same as a prism or the sky. But nope. So the observation of dot spacing with regard to wavelength through a diffraction grating is totally consistent with the model you've outlined, which is really satisfying.

[@markren626]

This super amazing explanation made me think of the animation of 3b1b’s fourier transformation animation, the little dots moving on the sine wave and add up their values is just like the process of wrapping a metal wire around a circle and find its center of mass!

[@manswind3417]

Quite a marvellous experiment and of great utility, as the instructor points out and I rightfully admit. However, as opposed to YDSE, wouldn't this experiment be a nightmare to actually execute? We are dealing in lambdas of the order of below microns here, so in the process of exacting our Ds across the wall, even if we miss the mark by a nanometer in making the hole we might mess up the whole pattern right? In YDSE we didn't have such a concern since there were only 2 holes so a slight error would only cause a slight shift in the interference pattern, but for diffraction grating wouldn't the error add up due to all holes and effectively yet a dark spot instead of a bright one all because of physical imperfections?

[@fahamidaani9597]

wow you explain it so easily

[@vardanhovakimyan7633]

good job, buddy! thanks

[@chaitanyavarma1747]

"Double slits are cool" Awesome 😂😂😂

[@bhaveshohal3390]

Excellent video.....

[@harshilkaswala1886]

awesome Vedic loved it

[@aashwinsharma1859]

Just understood the concept in 15 min which I couldn't understand in days. Great explanation

[@allaryyan6608]

wow..that is amazing, thanks alot!

[@navarundas1878]

great explanation..much appreciated!

[@poiuwnwang7109]

That makes sense to me, Khan.

[@abuhshadid5938]

You explained it just perfect.... You make some great videos on physics.... You really are a great tutor... It turns out that my teacher doesn't have any time to explain everything like you do... So I'm very much grateful to you, David SantoPietro...

[@bondlets2342]

Thank you so much! You guys are awesome!

[@tylerlitch3992]

What screen recording software do you use? I would like to know a good one that allows me to pause recording.

[@malezacaminante9577]

This videos are just amazing!

[@georgiaantoniou8410]

ELITE TEACHING SKILLS

[@adreekazafor2410]

i think i don't even need to go through the topic anymore thanks

[@vinaykumardaivajna2470]

Wow great thank you u guys are ....great...thank you so much.....

[@1Rise]

you explained the destructive concept perfectly and easy to understand.

[@intesar6341]

Thank you ... now its clear for me

[@lewiduressa]

This explanation is very clear. I read my physics book on this topic, and added with this video, it makes sense! Thanks

[@redrocz1]

great video!

[@rishabhattri6055]

Very well explained

[@banterbus4297]

thanks so much you helped me understand it so much better

[@antoniadukmenic627]

Thank you sooooo much! 💞

[@carolwang8647]

啊啊啊啊啊啊，下周就考物理了。希望能考好，好想去UCL

[@miyu6720]

khan academy saving my grades I FREAKING LOVE YOUUUU

[@wildmindentertainment2685]

Subscribed, very good explanation. We see stuff so superficially at high school that sometimes I must understand more graphically thr whole phenomenon and not just admit results as they would want us to do it.

[@sivasamymurugasamy3998]

wow...wonderful..

[@5vart5ol]

Dude! You really have to become a teacher! Cause the way you explain! You make it so it feels sooo interesting! Which it is! TEACH MORE!

[@smallbowl7143]

Thanks, but I'm slightly confused If d (distance between 2 slits remains constant), then at any time no more than 2 waves can be in phase. Furthermore in the maths used to find the equation dsin(theta) = n lambda, you say that the wavelength is the change in x and make a right angled triangle. As it is a right angled triangle the angle opposite the right angle must be the hypotenuse and therefore the two lines must not be the same length and the waves are still out of phase. If I didn't explain clearly then sorry but that's why I'm still confused

[@derdudernan]

Small Bowl I think I understand your question, so let me take a shot.. d*sin(theta) represents the extra distance light has to travel from one opening compared to another. The reason light from several different openings can be in phase is because that distance for those openings will be an integer number of wavelengths. So if the light travels say 2 or 3 or 4 or... extra wavelengths in distance compared to another opening they will still hit the screen in phase. Also, yes in the right triangle you talk about the hypotenuse is a little bit longer then the longest leg, it is assumed the rays are parallel when when leaving the slits, so it is an approximation. But since the distance between the slits is so small compared to the distance to the screen the angle is really small and so assuming they have the same length gives a good approximation, even on the scale of a nanometer. Hope I understood the question, hope that helps. Still attempting to understand it fully myself...

[@smallbowl7143]

derdudernan Since asking the question I studied more physics and came across small angle approximations. In very small angles it is assumed that sin(x) = x = tan(x) This is the reason it works as the hypotenuse is effectively the same length as the adjacent.

[@gausiyakhan6478]

Because of two coherent sources .in huygens theory every point are source .

[@yeonjin8]

First time watching an English explaination but still it's so good❤️👍

[@LanNguyen-iu3oe]

Thank you so much! your videos on diffraction and the slit experiment really helped me fully conceptually understand the process.

[@shashanksadafule]

How is path difference constant for consecutive waves. The theta is different for both of them

[@brianummel5602]

I agree. His explanation is wrong.

[@gabrieldobre8732]

The best explanation

[@smtusharibnesalam8688]

Where's the love button?

[@tajungnuksungpongen4339]

thanks your AWESOME....

[@DaDream6]

reflective grating vid would be dope

[@craetydonutkey1348]

For the deviated spot, i think if you just draw out all the possible waves on the same graph you could tell they are interfered destructively by their adjacent waves at each intersection. In other words, I think any space between the integer wavelength lambda will always be dark, resulting in discrete bright spots on the screen.

[@spookyaction]

good point