Total internal reflection | Geometric optics | Physics | Khan Academy

[@jrjubach]

i love how he hopes we find it "reasonably interesting," lol. not "incredibly" interesting or even "very" interesting. just "reasonably" interesting. :D

[@jrjubach]

@Enrique Duran Mynenko yes

[@jrjubach]

@Enrique Duran Mynenko You just asked me five days ago bro.

[@omaralsaheb9737]

Alive?

[@heluvsahona]

@@omaralsaheb9737 bro 😭

[@CubanSauce]

Man, why cant i have teachers like this? Mine just sits there and talks like i can imagine what the .....*.... he is talking about. Thanks.

[@bagyaaluthge1185]

Same💔

[@MrAlbashiri]

once again, I don't know what would I do without your videos. so much love to you Mr. khan

[@mileymy22]

1:26 to 2:45 is what i found most useful, thanks mate

[@NoahElRhandour]

0:38 i love that you always have such good examples to explain such phenomenons. this has actually something to do with the wave character of light. the example with the car is perfectly fitting. the light reenters the medium it just left due to its diagonal micro movements and looses speed. reentering the fast medium again, it made a curve.

[@sarahholland5980]

Sal, you are a lifesaver! Summer classes have us learning this whole playlist in 3 days and it's going to make up around 25% of the final. I was so stressed but 3 hours of sitting down and watching this playlist actually makes it manageable. Thank you, thank you, thank you!!!

[@SkatingAT]

Thank you, Mr. Khan! You are the one who helps me to escape from my boring physics lesson!

[@guiltypleasure5176]

I swear no one teaches like Khan Academy! This is amazing, I had been trying to understand this whole concept from other videos, but for some reason, all those teachers or speakers assumed that everyone is a genius and automatically knows what they are talking about so instead of explaining, they just carry on saying a bunch of words that I have never had of.

[@LAnonHubbard]

I appreciate the analogy of the car going from one surface to another. That's an easy one to remember.

[@SHAJ3304]

Thxs a million!! Khan Academy videos have been helping me for 2years now! Sal's the best at making complex things simple!!

[@freyasouter5329]

Thank you SO much! This has been immensely useful and makes far more sense than it did before I watched the video! Many thanks

[@Thebluedevil078]

Once you had explained total Internal reflection, I whipped out my scale and even tried it in practical....and it worked....Thanks for explaining in ruch simple words and making it understandable

[@laurensh3860]

This was the one part of my optics subject in school i never understood. Thanks for explaining clearly!

[@mathildeamz5182]

thank you so much ! I litteraly study in french and english is not my first language and i’ve learned more from this video than from class😭😭

[@Hello-qx4wm]

I need my teacher teach like you,interesting and easy-understanding

[@luisdarkangel]

Youve helped me in so many of my classes...... i hope you know a lot of people really appreciate this stuff. Thank you. Thank you so much.

[@shiksha1971]

Where have you been all my life *sigh*

[@zoeangermeyer3502]

This wil help me so much for my physics test tomorrow!

[@q_q123]

Thanks a lot. My teacher made the explanation complicated. This sums up what I need perfectly.

[@reiys97]

I found it reasonably interesting! Thanks! :3

[@AlphaNumeric123]

The core has a high refractive index and it is surrounded by cladding that has a very low refractive index. There is a "cone of acceptance" (where you seem to have gotten confused; the air to 'glass' transition is not fundamental to internal reflexivity) such that for snells law, rearranged and sin90->1 crit. angle = sin^-1 (1 / huge n). the argument approaches 1/inf. and sin inverse of zero in 90 degrees. That is to say, that only if light approaches at 90 angle will it escape. :3!

[@NikkiVee]

My teacher has been explaining it for the past hour and I had no clue what she was saying. I understood right away after watching this video!

[@Eddieftwz1]

Thanks for this video, helped explained this better rather in class. Fully understood the concept behind critical and total internal reflection. - grade 10 student

[@lmychocolate]

waaay better than my teacher. I love khanacademy

[@suhasbangari7852]

I want to keep it simple. You do great!!

[@_Rick_Astley_]

7:24 is a glitch in real life 3:29 also glitch 7:39 another one!

[@tobiaspattison184]

You have carried me through my GCSE's

[@lorrix95]

thank you! this video better my understanding :)

[@timclouter5644]

Reasoning it out, your explanation from 0:28 onwards was fantastic - it just immediately clicked. Thanks for your help!

[@SamuelAshwin1805]

This is great! Havin a physics test tomorrow! This really helped me to understand what TIR Is!

[@marriyumh]

Oh my God, they never told us where the 1 comes from!! Thanks a lot! ^^ You're so awesome! :D

[@allanfernz9356]

super AmaZing.....I'd rather bunk college and sit at home and learn from you......You"re amazing!!

[@twiggygordon3980]

Learned more in 6 minutes than an hour with my college professor... thanks so much.

[@Mellybeans0919]

This makes so much more sense!

[@zaravx]

Thx!!! This helps so much I hope I wont fail my physics exam

[@classifiedlevel1047]

The way u explain is top man 👌👌

[@MrGMXander]

Great video for understanding reflection,refraction and critical angles!

[@kldCF]

Thaaanks , that was really helpful !

[@HadiExtreme]

Thanks a lot man! I have an exam tomorrow, and you just helped me understand Snell's law and the whole theta critical thing a lot better!

[@ahadsafdarku3962]

Wow dude it’s been 8 years now u would be doing a job now right?

[@_Rick_Astley_]

Dang now its been 10 years

[@Channel-xi2ll]

These videos are the only reason that I'm able to pass my physics exam.. THANK YOU SO MUCH!

[@miltonweinhold6859]

i love your voice and teaching skills Sal, thank you so much for taking the time to make these wonderful videos you are awesome

[@dwightschrute3712]

Is this what causes all reflection? Do mirrors, for example, have such high refractive indexes that they reflect all light?

[@purvai4701]

That is a very good question

[@shensley011]

ooooooooooooooooooohhhhhhhhhhhhhhhhhhhhhhhhhhhh 1:40 shoot I GET IT now!

[@kpupforlife3745]

Man you js saved my grade tysm

[@fiona4541]

thank you! It only takes me 8 mins to understand what total internal refraction is. I can't even figure out what my teacher is teaching before watching this video.

[@sanketdoshi3451]

right through d basics ! nailed it ! Sal u rock !

[@devika6431]

Thanks a lot..!! It was very helpful 😁..

[@punhoching]

That's a great programme... It helps me a lot!!!

[@mohamedahmed8996]

Thank you very much i have a test tomorrow and i didn't know how to do it

[@heroofhell522]

MODY 14 me 2

[@heroofhell522]

+MODY 14 me 2

[@Ethereal__Girl]

Most beautiful channel i have ever seen.❤

[@goodidea9230]

Thank u! This helps me a lot doing my school works! An amazing and engaging lesson!

[@metastag]

I love this guy's calculator 😍

[@danielcoleman7156]

Sooooooooo helpful, my exam is tomorrow and this is really going to help

[@selamalemayehu6212]

Thank you so much, you made this waaaaay easier Respect🙌🙌

[@omkarshintre5695]

This video helped alot!!!!

[@armaghan1196]

Sal Khan is the GOAT🐐

[@kushal8406]

Thanks you very much for the video I was facing trouble understanding total internal reflection...... Thanks a lot

[@hanaahmeti8256]

You're a life saver Mr. Khan. Now I know I won't fail my physic exam.Lots of love 💜

[@jacobreich7059]

sir you just saved my life

[@vl2378]

bless you sal

[@taylordeasley2358]

Thank you so much!! It all makes sense now!

[@rizonemalang]

what a concept of fiber optics wow amazing thanx alot

[@senarafernando6540]

Thank you so much, you really helped me for my test!

[@lucindadewaal9511]

Thank you Khan Academy... You guys are always life savers !

[@nurinarifah9091]

helps me alot. thanks!

[@mayurkalsekar524]

The car example was brilliant

[@shroomish6462]

this guys a champion

[@immaculateson]

you are a GENIUS! Thanks alot

[@Xynomavro]

In our case -1 ≤ a ≤ 1 and b ≥ 1. And so, -1 ≤ a/b ≤ 1.

[@damidzcold4337]

Good

[@nikiytanaude3100]

Thank you SO MUCH!!!! This helped to explain the concept and reasoning of the critical angle.

[@yourdearestcas65]

thank you so much,you are the best Physics teacher in the entire world!! by a student from HONG KONG

[@abhimurali3911]

The best explanation ❤️👏

[@FireVortex720]

Cleared things up for me, thanks!

[@muhammadmuzamil4281]

thank you so much, man. my teacher has such a strong German or Austrian accent and its hard to understand anything thanks so much

[@Xynomavro]

A good point but sin(θi)/n cannot be greater than 1. No material has a refractive index of less than 1 and sin(θi) cannot be greater than 1 which means sin(θi)/n will always be between -1 and 1, inclusive. Hence, Snell's law is valid.

[@hsmrocks1fan243]

Thank you SO much for this!!!!

[@xXxlongboarderxXx]

This really helped a lot, I'm 14, i need to learn this in foreign German though :c this is going to be so hard xD

[@balqismohdridhwan4628]

NZVON where did you come from?

[@nalod2087]

Arolema Prarath wat

[@MunkesGamingDenmark]

helped me out alot. Thank you.

[@mrpikachua]

thanks, this helped alot

[@mihirshah3881]

Thank you Mr.Khan ,your videos are very helpful .

[@t.z8175]

Thank you ，that was really helpful

[@kudakwashe326]

thank you so much was very halpful😉

[@thegarbageman21]

@arenms believe it or not many people enjoy reading / learning. I read an article about khan and his academy in a magazine a while ago and he appears to be a very humble guy genuinely wanting to help others. He enjoys reading which is how he learned all this stuff. And honestly what he teaches is relatively basic stuff. Im a medical student and now that is mentally / physically draining.

[@sakinahassan2065]

Nice explanation 👌

[@Gasdemjewz]

4:50 u can just calculate it with ur calculator and put the unknown given as an X

[@icathene]

Nailed it.awesome explanation

[@indieca13]

i'm gonna mention this to my teacher so i'd sound smart. yes. thanks.

[@majopmful]

very good . Thank you so much.May Lord bless you

[@ArturoG21]

So is it safe to assume that regardless of the media the ray is initially in and the final media it is in, we can use the media with the lower index of refraction in the numerator, and the higher index in the denominator? Because there's been a couple situations where I get undefined errors in my calculator. For example when a ray goes from glass to air and I use the glass in the numerator and the air in the denominator because I'm thinking n1 = glass since it was in glass first.

[@Xynomavro]

I see what you mean now. Did you watch the video? It explains what happens when θi becomes greater than the critical angle - you get total internal reflections. Snell's Law is still mathematically valid, given a certain set of circumstances.

[@tirsoacuna1356]

Thanks a lot for this video! It's nice to see you're constantly uploading lots of videos. Many of them are so helpful! Thank you so much for keeping this channel up and going.

[@kevinlawrence17]

You explained it very well sir :D

[@amithavenepally8486]

Amazing , just amazing 👌🏻👌🏻👌🏻😬😬😬

[@idiosyncraticidiott5015]

Thank You

[@arabian-qv5wy]

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[@Hi-ny6iq]

Thank you so much

[@ryanltn]

thanks a lot!

[@Praveenkumar-cp2cb]

Thank you sir!!!

[@yashvardhan8982]

Man ,you are awesome