Thin Film Interference (part 1)

[@CntrBrdr]

Whenever I see this phenomenon I think back to my classes with Wolfgang.

[@robin2080]

I remember when Dr. Logan first showed us this!!

[@bulleonevenement6904]

Great experimentation ! Thanks. Bulléon from #nantes, # France 🇫🇷🇪🇺😉

[@letseat1098]

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

[@lesshome5689]

Can you zoom in in to the part @ 2:43 where the air bubbles mixing with each other, i would like to have a closer look how colors mixing there?

[@stud000000079]

Why does disturbance or chaos occur at lower sections when the Top half of the film had become dark?

[@NatSciDemos]

Gravity is constantly pulling down on the soap film, so the thickness down at the bottom is increasing as the thickness at the top is decreasing. Turbulence and other complicated phenomena makes the film look swirly and non-uniform at the bottom of the ring.

[@wedmunds]

Does the entire film become thinner than the wavelength of purple light at the end?

[@NatSciDemos]

When the film appears dark that means that the film thickness is less than the wavelength of all the colors visible by the camera (and humans).

[@bibeklalkarn3494]

@@NatSciDemos so can we use uv camera for that part?🤔

[@Harukamirai1801]

Thanks for it It helped me

[@NatSciDemos]

Glad to hear that!

[@jupa7166]

What is the liquid so robust that it doesn't break even when extremely thin?

[@NatSciDemos]

It's just water, dish soap, and a little dash of glycerol.

[@emre1929]

Thank you all for responding comments !

[@shivohcn1684]

What is the reason for the appearance of blackness after a while ? Thanks in advance

[@NatSciDemos]

Over time the soap film in the ring gets very thin at the top due to gravity pulling down on it. When the thickness gets to be less than about 50 nanometers then destructive interference occurs in the reflections of all the visible wavelengths, and so we are able to see straight through the film to the black background.

[@shivohcn1684]

Thanks...but why it is all destructive interference why it is not able to show constructive interference

[@NatSciDemos]

The film has two sides--a front and a back. When incoming light reflects off of the front surface, the phase changes by 180 degrees relative to the incoming light (if you think of light as a sine curve, then the reflected signal flips upside-down relative to the incoming signal, so where there was a maximum there is a minimum, a minimum a maximum, etc). When the incoming light reflects off of the back surface, the phase doesn't change. When the distance between the front and back surfaces is small compared to the wavelength of the incoming light, then we are able put these two reflections together and they cancel out and we see no reflection.

[@shivohcn1684]

I am a btech 1st year student . thanks for providing me the answers

[@denzellnigel8372]

@@shivohcn1684 noob

[@MushroomStorm123]

Why is there no interference to get colored reflections when using thicker mediums?

[@NatSciDemos]

We see the effect when the soap film is thin because the reflections off the top and bottom surfaces are close enough in space for them to interfere with each other.

[@MushroomStorm123]

@@NatSciDemos So if i had a 1cm thick transparent layer and a light source that emits monochromatic light with same wavelength, it still couldn't interfere? Even if the light falling onto the surface would be spread out enough so that the reflection from both the top and bottom surface would guarantee to cross each other?

[@bass712]

Mithil sir 🙇‍♂️

[@racchitjain475]

So if we see this from the other side will it show colours? Since the Rays are being refracted?

[@NatSciDemos]

Here we're looking at colors that are reflected off of the front of the soap film when we shine white light on it. An application of this idea is the anti-reflection coating used on camera lenses. In that application, light with a certain color (wavelength) can pass through the lens more efficiently than the other colors.

[@akshatdholakia9275]

Who is a Allenian

[@AlexanderShubin555]

nice