Timeline for Destructive interference and energy conservation
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
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| Sep 25, 2022 at 11:53 | comment | added | anna v | l;ets tp this here, as we do not read the situation the same way. In the MIT video I link the energy goes back to the source, for example. In this case my opinion is that the energy goes finally to thermal energy, and I am trying to explain my POV with the ball example. For me if there is total destructive interference, black, the energy has to turn up as thermal energy. | |
| Sep 25, 2022 at 8:43 | comment | added | flippiefanus | In the context of the OP, you are saying that the reason that thin film appears dark is because the light is absorbed. Now you argue that it is because of momentum conservation. That is nonsense. Light is reflected off the interfaces with negligible energy loss, regardless of the fact that momentum is conserved. This is easily confirmed by experiment. | |
| Sep 25, 2022 at 4:56 | comment | added | anna v | @flippiefanus in the simple ball scatter, ball in x derection hitting wall and bouncing back in x directioin, it looks elastic, but because it returns with the negative momentum, of the original direction, it means that the wall must take up twice the momentum, so momentum in the x direction is conserved. | |
| Sep 25, 2022 at 4:50 | comment | added | anna v | @flippiefanus No, the ball scatters off the wall, it is not absorbed! But momentum conservation imposes the need of energy loss, and that energy has to be somewhere. The same with the light beam. | |
| Sep 25, 2022 at 4:32 | comment | added | flippiefanus | In other words, you are saying that all the light would be absorbed because of the momentum transfer caused by the reflection. Obviously this does not happen. | |
| Sep 25, 2022 at 4:13 | comment | added | anna v | @flippiefanus classically , as light, the scatter is with the whole lattice that makes up the film, the momentum arguments are the same for reflection. For momentum conservation the whole lattice should move with twice the momentum of the impinging and reflecting light, which implies energy loss from the beam that has to go somewhere, and I guess heat, unless the film vibrates, and then again it will go to heat | |
| Sep 25, 2022 at 4:09 | comment | added | flippiefanus | Your microscopic description would not give interference, because if there is momentum transfer, the scattered particle would become entangled with the scatterer. For light, it is better to use a linear model in terms of reflection and transmission. | |
| Sep 25, 2022 at 4:00 | comment | added | anna v | @flippiefanus If there is a scatter, and reflection is a scatter, there is always momentum transfer and because of this some energy lost (ball scatter on the wall) . That energy ends up in heat is all I am saying. ( relevant my answer here physics.stackexchange.com/questions/248726/…) | |
| Sep 25, 2022 at 3:53 | comment | added | anna v | @Not_Einstein I do not think that the return to the source can be mathematically described with classical maxwell equations. | |
| Sep 25, 2022 at 3:52 | comment | added | flippiefanus | This answer is not correct. The thin film does not need to be absorbing. So it would not have the ability to convert the energy into heat. | |
| Sep 24, 2022 at 23:34 | comment | added | Not_Einstein | How does the referenced video show the quantum mechanical dependence of light? | |
| Sep 24, 2022 at 22:40 | comment | added | FlatterMann | Can you give me an actual physical example of a thin film that is dark? If that was the case, then deep black would be the cheapest paint of all... we would just have to make a really thin layer of paint of any color. That is obviously not so. I think the question is based on an unphysical understanding of the properties of thin films. My guess is that it implicitly assumes that the dielectric constant of the material of the thin film goes towards infinity. If it doesn't, then the thin film will surely not look dark. It will become ever more transparent the thinner it gets. | |
| Nov 24, 2017 at 16:20 | vote | accept | user157588 | ||
| Nov 23, 2017 at 5:20 | history | answered | anna v | CC BY-SA 3.0 |