27 Inteference & Diffraction - Thin film interference

[@StarShootex]

Big youtube channels like Khan Academy explained it well, but the formulas for constructive and destructive interference looked so wrong and I wasn't able to conceptualise what was actually going on. This is honestly the most helpful video I could find regarding this topic. Thank you so much!

[@CogverseAcademy]

StarShootex very nice of you, thanks a lot! You're welcome, good luck with Physics!

[@primumdiscenti]

@@CogverseAcademy Thank you sir, From one year after

[@SW-2010]

​@@primumdiscenti Thank you sir, From 4 years after.

[@adamabera]

This is the most informative video on thin film interference on KZbin. Thank you!

[@madspihl]

Oh, the clarity of the reasoning here is just brilliant.

[@sarowerrafin5168]

love the way he teaches

[@Tom-sp3gy]

This is the most comprehensive video on thin film interference

[@CogverseAcademy]

Thanks!

[@pronoysengupta8601]

his handwriting in reverse is better than mine normally! XD! Great explanation though sir!! :)

[@manvirsandhu508]

pretty sure its some program that reverses the image. hes not writing in reverse

[@maimoonamumtaz6376]

I think there is another mirror..

[@bijoykhanal7945]

😂

[@sccm100]

Thank you. You made this very clear. Also your other video on phase shift upon reflection helped a lot.

[@CogverseAcademy]

You're welcome :) Thanks!

[@salambostaji9315]

Thank you very much!!! This really saved me, I have an upcoming exam and I was so lost. This made everything so much easier.

[@CogverseAcademy]

You're welcome! thanks for watching

[@Bennet907]

After all i found a clearer picture of thin film interference, thanks a lot professor (⁠^⁠^⁠)

[@juranliu9445]

Lambda should be different in different medium. So I think there should be a coefficient of n1/n2 or something like that.

[@_John_Sean_Walker]

They usually use 1 for n1.

[@phucdeo5247]

correct. I think it should be lambda/n2

[@jayvyas1827]

Thanks for such a nice explanation!!👍👍

[@andrewjustin256]

You elucidated the topic in an intriguing way that beguiled me totally!! Thank you! By the way, what is your name, sir?

[@TheMex6991]

Why'd you stop making such great videos???!?

[@kalkidanberhanu7708]

best explanation for thin film interference

[@StudywithmeinPakistan]

Excellent. From Pakistan

[@StudywithmeinPakistan]

Can u share a behind the scenes arrangement, that how you make video by displaying on some glass in front of you.

[@alyxx001]

thank you!

[@tauraigombera]

This is super clear. Thank you!

[@CogverseAcademy]

TAURAI GOMBERA our pleasure, thanks for watching!

[@KrisEditz29]

Thanks you very very much sir, really beautiful explanation,helped me to get it right on the first time,thank you

[@CogverseAcademy]

Thanks for watching! :)

[@leticiaaguirre8126]

"well done m'boi" **mr.krabs voice**

[@nandanadileeep]

Thank you sir...your teaching is amazing .....🤩🤩🤩🤩

[@margoburova5792]

Thank Pythagoras, I finally found something that explains it well. I've read through four other souces and it seems like I'm to stupid to understand either of them. Anyways, thank you very much!

[@ژزر]

Thx❤ , I'm from Iraq and I have benefited .

[@maitreyeeguha6213]

For constructive interference, why does the phase change by 180 degree at the surface of the two interfaces of refractive indexes, n1 and n2?

[@SalahuddinRahat]

osthir bhaii

[@benxiao5966]

omg this video was so helpful

[@CogverseAcademy]

you're welcome :) Thanks for watching!

[@alpdemircioglu8899]

Simple and clear

[@الاستاذحسينعلييعقوب]

Thank you sir - - - can l say that we will deal with ( 1/2 lamda ) as a distance because it is added to L1 or. L2. Thnk you again sir

[@johngordon8513]

this is all awesome, however if you or someone could please clarify something for me. i understand that the blue ray will be inverted or phase shifted by 180 degrees. Why is 180 degrees = lambda/2 ??? is it because a full wavelength is technically 2(pi)??? like i think that its just because its a wave and one full cylce of any wave is 2pi, right? so its lambda/2 because 180 is 1/2 a full lambda??

[@CogverseAcademy]

The short answer to your questions is: yes. As the phase increases by 2pi, the wave travel one wavelength lambda in one period T. Thus, because when the wave reflects off an interface with a higher n value its waveform flips, its phase shifts by pi. Visually though, it looks "as if" it had traveled an additional distance lambda/2. Does that make sense?

[@johngordon8513]

@@CogverseAcademy yes, thank you for responding so fast!

[@maheshmeena8553]

Wonderful video

[@CogverseAcademy]

Thanks!

[@crushlux]

Hello, I have a question. Why haven't we use the n1 or n2 in both of the formulas ? Aren't we supposed to use them ?

[@CogverseAcademy]

you would use them to find lambda in the film. If, for instance, you were given lambda_air in medium n1, then n1*lambda_air = n2*lambda

[@crushlux]

@@CogverseAcademy thank you for your reply

[@misterprice100]

hi in first example I don't understand something.I knew that for oil on water (similar the first exercise where the n2>n1) the distructive eq. was equal to 2e=ml1, where l1 is lambda in function of the rifracrtex index n (l1=l0/n, l0=lambda in vacuum, l1= lambda in the matter). In this link there is an exaple of that I ve just wrote :online.scuola.zanichelli.it/cutnellelementi-files/pdf/InterferenzaLuce_Cutnell_Zanichelli.pdf - pag 436). Could you explain me why this difference ? Regards

[@andrewjustin256]

Would you please verify one aspect about it to be accurate that I had learned from one resource stating that lambda is to be divided with the index of refraction of the medium of whose thickness is being calculated; so, it means the equation becomes: 2t=(m+phi)lambda/n.

[@CogverseAcademy]

Yes, the lambda denotes the wavelength measured in the film. More details here: kzbin.info/www/bejne/h5yUnpqpd7yYrLcsi=FchsisuUfxQ_0LMR

[@dhruvkumarjiguda5415]

Don't you have to account to for the changed optical path for the second ray??

[@netwiz2]

I still do not understand why they did not destructive interference did not occur at first?????

[@曹原铭]

great video very helpful thx

[@ryu.l2264]

how about if n1 bigger than n2 and having 2 times of reflection in n2 medium?

[@mohammadasad5637]

So the wavelength is observed from the first medium, right? So lambda is the wavelength of light in n1. Correct me if I'm wrong. But I've seen many citing lambda as the wavelength in the thin film. But for instance if I consider the optical path length of (L1-L2) rather than the geometrical path length, then it would be = 2*n*thickness. And if the indented wavelength in the equation is considered to be that of the light in the thin film, then 2nt =(m+.5) (lambda of the light in air or first medium/n) NB: Considering the given wavelength in any problem is that of the light in first medium and n is the refractive index of thin film. Which really messes the equation:( Please check this out also: kzbin.info/www/bejne/jHSzepuan9OJeKc

[@fdl2]

Can you please explain why there is no phase shift when wave travels from film to air ? i know the fact is so obvious (n film > n air), but still dont get it

[@CogverseAcademy]

ox clement i looked around for a clear response as I figure someone might have clarified this already. Here is the link: physics.stackexchange.com/questions/32122/phase-shift-of-180-degrees-of-transversal-wave-on-reflection-from-denser-medium. Technically this goes beyond the scope of what is covered in this channel but hopefully it clears things up for you.

[@tquiz7526]

it took me some time but i get it , thx

[@rebeccafu2745]

I'm kinda surprised by his ability to write things from backward to forth...

[@JimmyCHOW]

but you frogot the wavelength will change in different medium compared with the one in the air.

[@CogverseAcademy]

Hi, here is a better version of the video where that is explicitly covered. kzbin.info/www/bejne/mqSrhXlqg5mnrLssi=_WXj2UKfO3FjgidT

[@kori4580]

I don't understand what "m" stands for in this setting. I know for the slits it means the maxima but how does that relate to thin films?

[@CogverseAcademy]

Marcus Aurelius m is an integer that determines the amount of shift between the two reflected waves. If you set the path length difference equal to m*lambda then your interference is constructive, if you set it equal to (m+1/2)*lambda then your inteference is destructive. Make sense?

[@kori4580]

thank you :)

[@bharatjoshi9889]

How did you know that phase shift is lamda/2

[@CogverseAcademy]

Hi, let me know if this makes sense: kzbin.info/www/bejne/h3Kno6iXfqaiibc Essentially as the waveform flips, its phase shifts by an amount pi. In terms of wavelength, that is equivalent to half a wavelength.

[@kobusingyeracheal2482]

@@CogverseAcademy That comes from the relationship between phase difference and path difference

[@jcv71]

Will this apply for holography?

[@vvvvvv-sd4pw]

Can anyone tell me what delta x actually means or does it now matter and the final equations are what’s to be used Edit: also, if there isn’t any phase shift at all, how would you do that?

[@ywy1628]

Thankewwwwww it helps a lottt!!!

[@shadyashraf1031]

what do n2 and n1 refer to ?

[@shadyashraf1031]

@Hasham Khan too late Ive failed the course .. thanks tho

[@shadyashraf1031]

@Hasham Khan lol I am kidding . I just find the man in the video hot and I wanted him to reply because I am horny

[@shadyashraf1031]

@Hasham Khan dude man up and have some respect for the elder

[@shadyashraf1031]

@Hasham Khan Yo dont make me put you on my list 🙄

[@shadyashraf1031]

My Vibration and Waves final test was super Hard that I got out with a fat ass C grade .. higher than most others

[@AK-fn7ro]

why lamda divide by 2 why not 3 lamda divided by 2

[@CogverseAcademy]

AK 47 47 47 because the lambda/2 shift only occurs upon reflection on a surface with a greater index of refraction. There is only one such reflection here.

[@AK-fn7ro]

Thanks sir now its clear to me

[@selmanawel7556]

Besttttt

[@misterprice100]

... pls see also this example in that link: kzbin.info/www/bejne/oqG2eHZrbNOmnZI. Something seems wrong. Let me know how do you think. Regards