Thin Film Interference part 1 | Light waves | Physics | Khan Academy

[@papasgottaeat]

I got mad and almost threw my laptop out of the window when trying to visualize this phenomenon in an optics book. You saved me hard. Thanks a lot!

[@faisaleclair9293]

I thought i was the only one

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Why do I feel you

[@bhadrachatterjee9163]

Ahhh my man!! Same!!

[@edu_in_iitg]

I was the same

[@mackss9468]

I just wasted two hours trying to learn this and you explained it in 12 minutes. Thank you.

[@Nepeta-Leijon]

i love this side of youtube!! im in college for a music degree. i like science, but i dont take science classes because they arent required for my degree. watching science videos online gives me the chance to learn this stuff :D i LOVE it omg

[@limesther7000]

my textbook did NOT clearly explain why the path-length difference was 2t. Your explanation is so simple and clear. Thank you!!

[@Sgbll]

You are probably saving my physics exam. A big thank you for all the videos

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Hi from 5 years, 😄 What are you doing now in life?

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Hi from 7 yrs....what are u doing now😊

[@gabedarrett1301]

David has a talent for making complicated things easy to understand! Thanks!

[@soumyapriya6110]

Elon 😂

[@Marina-ke3km]

I have a homework question that is asking me to show that the reflection cancel each other out when ns>n1>n0, (vs

[@MrPoffersher]

Dat cliff hanger do.

[@goddess_ofchaos]

THANK YOU SO MUCH FOR THIS VIDEO I was struggling so hard, my professor could never have explained it better!!

[@citylovesme]

Same situation for me tooo 😭

[@nothere941]

David is my fav on the whole Khan academy

[@megan282]

I was preparing for physics exam, couldnt understand this topic even in my own language. This video really helped, thank you a lot. Btw, your voice is amazing. Good luck!

[@mha5289]

I was under the impression that you only get a phase shift if you are going from a lower index of refraction to higher. Doesn't that mean that we don't get a phase shift from oil to water because oil has a higher index of refraction?

[@soccerchinchilla]

I think you're right, but there is a phase shift from air to oil, and there isn't another one to balance it out so the condition is reversed.

[@MasterKey2004]

@Kaleb unknown maybe a bit too late

[@katerinasanticola8499]

But water has an index of refraction of 1.333 (4/3) and oil somewhere around 1.5. That means that since v=c/n, the velocity of the light wave in oil will be less than in water since velocity and index of refraction are inversely proportional if the constant c is constant (which it is, speed of light in vacuum). If water has a smaller index of refraction then a wave has a larger velocity in water.

[@SA-sq7sf]

well dats the point i waz thinkin' about

[@saleemsabid]

Katerina Santicola exaxtly 🙄

[@silverphoenix_1756]

blew my mind within the first minute. Always wondered what those colors were in bubbles.

[@MoatterAqeel]

Please set this playlist .... everything is here and there

[@JAndersonGhost0326]

The trick is if the wave bounces off a higher index of refraction, ie slower speed, it'll phase shift by pi. If you compare the two bounces, odd symmetry is odd integers of lambda and even symmetry is even integers of lambda.

[@ourtamilnadu9011]

Beautiful explanation.nobady can explain this concept in such a way, except you.

[@neurobiogirl]

THANK YOU!!!!!!!!!!!!

[@ray1351]

some of my friends were having issues understanding this videos but just incase anyone else is having any confusion - path length = wave length

[@yammay]

Sorry, late reply, but path length and wave length are NOT the same things. You can have many wavelengths (λ) in a path length, as the path length is the length from where the wave starts to where it hits the screen. Just wanted to put that out there for other people who see the parent comment.

[@vishwapranav721]

Holy moly thanks a lot!!!!!!

[@markjarc8621]

You got it wrong here. Extract from the article from wikipedia: There will be a phase shift upon reflection from the upper boundary because n_airn_ water. Water has smaller refractive index so it is faster medium than oil. (speed = c (speed of light) / n (refractive index)).

[@xlogn]

+Mark Jarc its the sane thing elementery class rule when a light is in a denser medium the speed of light is slow as compared to that in vacccum

[@ChristianMay21]

He said "for the sake of argument"...

[@pranshkhubchandani8102]

Khan academy is best

[@sabutkharizona7095]

But what if the light come in a certain angle? How do you explain that?

[@abhisharma1728]

why there's a pi shift when the reflection takes place with a slower medium??

[@inspire191]

I don't if you are still wondering about it but the answer is Stoke's Law.

[@srirampatnaik9164]

@@inspire191 Isn't stoke's law related to viscosity?

[@inspire191]

@@srirampatnaik9164 yes it is..and then there is another law by Stokes which describes phase change experienced by waves in such conditions.

[@srirampatnaik9164]

@@inspire191 Ah okay thanks

[@swethav7299]

Also phase difference is half of lambda.. how??? x = 2nt cos r - ( 1/2 lambda)

[@psubham3015]

God bless you sir ❤️

[@ellablakeborough1282]

my textbook was literally useless in explaining this thx!

[@AdriansNetlis]

Just a note - seeing how you observe the ray in this scenario, it looks like they rray must be coming directly from the eye. Are we talking about emissive eyes? Otherwise the delta x would not be 2t, but instead 2t/cos(a) where a is the angle of incidence of light. Oh, right, my assumption is not accurate either since the light would change direction as being refracted, thus also changing path length.

[@alicebrus2703]

Make one on Newton's rings

[@achingaster1199]

Thank you.

[@YAC270]

Thanks mate!!

[@mashrafirahman2027]

Suggested by our buet topper Meftaul Alam Siyam.I'll show my comment to him when I meet him In Shah Allah

[@kanishkkaushik780]

Low to high, phase shift of Pi.

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[@danieltroconis6805]

Physics 130 exam? Lol

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you saved my life sir hehe ^^

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Yes he is still saving 😉😂😂😂😂😂😂

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[@markcavendish7148]

Best explanation on whole of you tube.

[@aniruddhavichare5425]

thankyou!

[@utkarshsingh695]

Jai Shree Raam

[@pmat2757]

Oil has a refractive index higher than water, if so how can light travel slower in water . there must have been no phase difference

[@junkyarddog723]

Here the vacuum really looks like space vacuum- *Totally black* 😊...

[@neelamacharya1979]

awesome!!!

[@orchoose]

I dont understand how exactly thin film filters certain wavelenghts , is it bc of phase shift? It it bc some wavelenghts get constructive int whan reflecting and destructive whan refracting?

[@anandapatmanabhansu]

Sir is the velocity of water is more than that of oil

[@MaeverickCall]

Let's call the reflective index as n. If n of oil is 1.1, n of water is 1.333, Light travels from a less dense medium, to denser medium will slows down. Just like moving your hand in air, compared to moving your hand in water. Whichever medium is denser, will slow down the speed of light

[@h7opolo]

2t is only accurate is you are considering only 90 degree interactions.

[@chrisb766]

Except oil is slower than water! So there wouldn't be any phase shift at the second interface.

[@ahmedibrahim9217]

how does interference occur when sun light isn't even a monochromatic light ?

[@wolfie6175]

Different colours show constructive and destructive interference on the basis of their wavelength at any given point . Read Concepts of Physics part 1 by HC Verma : chapter Light Waves if you havent already

[@ahamedakmal7104]

at 2:49 , how can wave 1 and 2 meet to interfere if they are parallel

[@blzKrg]

This is drawn in 1D, think about the waves as 2D as in young's double slit and then you would understand how they interfere.

[@ahmadsyamimarsyad6431]

So basically the wavelength is no longer considered as coherent sources as one is being shifted by pi?

[@edis9493]

What is to comment on the ray of light reflecting from the bottom surface in the water?

[@commonscience3418]

Nice video what is the scope of physics?

[@abdulmoiz6256]

thanks!!! :))

[@Nepeta-Leijon]

why does light shift 180° qhen reflecting when it reflects??

[@Nepeta-Leijon]

like... what makes the light shift that way? (be as technical as you want! using obscure words will just give me more to learn XD)

[@wailamirza1084]

Look light shifts when going from a region of low refractive index to high refractive index because of the change in velocity because these two are inversely proportional to each other so when it moves to a region of high index it's velocity changes and when it's velocity decreases it bends from it's original path because of which if we compare these two the angle will shift

[@adityabilgundi]

MISTAKE...... ! actually the total path difference between the the ray reflected at the first surface and the ray reflected at the second surface should be = 2( refractive index of first medium )x(thickness of first film)

[@syedifraz2674]

you noticed he draw a triangle and called it an eye

[@AdityaFingerstyle]

Take a closer look

[@mrigank7977]

Syed Ifraz hevuh

[@letseat1098]

Sir, what are the factors affecting the thin film and how to protect the thin film?

[@habeshatechpro4350]

Stupid comment

[@swethav7299]

How is a light ray partly reflected and partly refracted?

[@ALFPAJARITO]

Dear khanacademy: If "n" can be any value why the film needs to be "thin"? That is, if the film is "fat" why will not be any interference? What is the limit value for "n" that suports an interference pattern? Thank you.

[@SaraKhan-jb3sr]

You may have probably got the answer, anyway let me explain something I read earlier. That when the film is much thicker than the visible light wavelengths, the effect permits nearly all of the spectrum to be seen and the resultant is Patten less and kinda whitish. On the other hand when the film is more thinner only certain colors are permitted and the result is usually one color or a mix of two till three colors which is more intresting and colorful pattern,used in various things.

[@ALFPAJARITO]

Dear Sara: Thank for you answer. Just one more question: in a bubble or oil layer you usualy can see almost all the visible colours from red to violet, so that means the film is enough "fat" to allow seen of all visible spectrum; that is all colours are permited and we still can see the interference (no whitish). I know in the practice if the film is fat you can not see the interference pattern, but still can´t understand why and I asume that an ecution can demonstrate that, could you please give your avove explanation in numbers or formulaes as an example I can understand? Best regrads

[@ankushraj9583]

Shouldn't the path difference be optical path difference and should be 2mu(t).

[@goodstudentsmarriedbooks6945]

I am from lraq... Thank you❤️❤️❤️❤️

[@s.mahapatra1275]

Thanks you very much!!!

[@garvitpandey6459]

Delta X for oil would be n times 2t, where n is the refractive index.

[@garvitpandey6459]

We consider optical path length not normal length

[@needywallaby2030]

Why no f body explained the pi shift before, bro here did it perfectly

[@Sriharika2305]

i guess delta x=2ut where u is refractive index of oil

[@vinayjawahar7983]

Why is it happening? Apart from rule.. :/

[@sinlingang8146]

Sorry...What is 'pie' shift?

[@FinLogan]

180 degree displacement in the x axis

[@adolphmatjukotja7096]

Sinling Ang... That simply means that the wave changes phase

[@mistsu1171]

it means that the waves are lagging 180 degrees behind the other.

[@rosh9318]

It's destruction a case in interference think I replayed you soon lol

[@ricen0odle]

holy shit thank you

[@James-yf8il]

Goat

[@themultigamer5682]

But speed of light in water isn't slower than oil thats majorly confusing. Y u do this.

[@purvai4701]

They literally mentioned the value of the speed of light in oil why do u think it ain't slower?

[@perceptron9834]

No angel no reflection 😅

[@yaduvanshi946]

Today attendance

[@arifffarhanrahdi9424]

The equation should be 2dn = m(lambda)

[@neethy1836]

OMYGOSH WHAT DO I WORRY ABOUT

[@stunningworld9815]

too dificult

[@enoki5843]

sir ... i think u πshift it wrong..sorry...but..am i right?

[@whenyoudiporeosinmilktheyb8329]

I am so lost

[@robiyonas1401]

you should have chosen a better diagram

[@vaishnavichavhan4245]

Nak ke nak me bat kr rhe kya🙄

[@adityadeveloper8775]

Very bad diagram

[@rumiratempest6279]

Tysm sir

[@richlovepherodin6250]

Thank you.