Total internal reflection | Geometric optics | Physics | Khan Academy

[@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

[@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 😭

[@mileymy22]

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

[@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.

[@zoeangermeyer3502]

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

[@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!

[@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.

[@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😭😭

[@SkatingAT]

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

[@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

[@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!!!

[@LAnonHubbard]

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

[@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!

[@suhasbangari7852]

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

[@Hello-qx4wm]

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

[@q_q123]

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

[@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

[@tobiaspattison184]

You have carried me through my GCSE's

[@laurensh3860]

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

[@shiksha1971]

Where have you been all my life *sigh*

[@lorrix95]

thank you! this video better my understanding :)

[@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

[@reiys97]

I found it reasonably interesting! Thanks! :3

[@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.

[@twiggygordon3980]

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

[@timclouter5644]

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

[@_Rick_Astley_]

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

[@allanfernz9356]

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

[@SamuelAshwin1805]

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

[@Channel-xi2ll]

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

[@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.

[@zaravx]

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

[@Mellybeans0919]

This makes so much more sense!

[@shensley011]

ooooooooooooooooooohhhhhhhhhhhhhhhhhhhhhhhhhhhh 1:40 shoot I GET IT now!

[@Xynomavro]

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

[@marriyumh]

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

[@metastag]

I love this guy's calculator 😍

[@arabian-qv5wy]

اشاهد هذا الفيديو عام 2022 ومر عليه 12 عام . اتمنى من يقرأ هذا التعليق يترجمة ويفكر في تعلم اللغة العربية لأنها رائعة

[@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

[@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.

[@danielcoleman7156]

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

[@armaghan1196]

Sal Khan is the GOAT🐐

[@MrGMXander]

Great video for understanding reflection,refraction and critical angles!

[@classifiedlevel1047]

The way u explain is top man 👌👌

[@kushal8406]

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

[@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

[@jacobreich7059]

sir you just saved my life

[@mayurkalsekar524]

The car example was brilliant

[@hanaahmeti8256]

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

[@Ethereal__Girl]

Most beautiful channel i have ever seen.❤

[@kldCF]

Thaaanks , that was really helpful !

[@shroomish6462]

this guys a champion

[@damidzcold4337]

Good

[@selamalemayehu6212]

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

[@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

[@vl2378]

bless you sal

[@devika6431]

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

[@taylordeasley2358]

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

[@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

[@goodidea9230]

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

[@lucindadewaal9511]

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

[@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

[@omkarshintre5695]

This video helped alot!!!!

[@senarafernando6540]

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

[@punhoching]

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

[@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.

[@nurinarifah9091]

helps me alot. thanks!

[@idiosyncraticidiott5015]

Thank You

[@Xynomavro]

n cannot be less than one. The refractive index of a vacuum is 1 and no material can have a refractive index lower than vacuum.

[@kudakwashe326]

thank you so much was very halpful😉

[@sanketdoshi3451]

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

[@abhimurali3911]

The best explanation ❤️👏

[@rizonemalang]

what a concept of fiber optics wow amazing thanx alot

[@Hi-ny6iq]

Thank you so much

[@mihirshah3881]

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

[@Gasdemjewz]

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

[@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

[@immaculateson]

you are a GENIUS! Thanks alot

[@ryanltn]

thanks a lot!

[@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

[@Ivory1340]

THANK YOU THANK YOU THANK YOUUUUUU

[@Coops99]

I don't understand why light totally internally reflects in fibre optic cables. The light is going from fast (air) to slow (glass), so wouldn't the light bend towards the normal (or towards the walls of the cable). I am assuming that the walls of the cable are glass?

[@FireVortex720]

Cleared things up for me, thanks!

[@mrpikachua]

thanks, this helped alot

[@Mr_Wayne93]

well explained

[@kayladaley624]

Thank u

[@indieca13]

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

[@hsmrocks1fan243]

Thank you SO much for this!!!!

[@Praveenkumar-cp2cb]

Thank you sir!!!

[@t.z8175]

Thank you ，that was really helpful

[@majopmful]

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

[@birdmanbird4374]

woah

[@sakinahassan2065]

Nice explanation 👌

[@ASSHOLELA]

i.e by snells law sinI/sinR = n, then R = sin-1( sinI/n), but what if sinI/n is greater than zero, then there is no such thing as Sin-1(x>1), and so Snell's law breaks down. But If snells law breaks down then how could it be mathematically valid?

[@ASSHOLELA]

I once asked my science teacher WHY snell's law faces a singularity at i = c and total internal refraction occurs and he was stumped!