Why does oil show so many colors?

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Discussion Overview

The discussion revolves around the phenomenon of color display in oil when exposed to sunlight, particularly focusing on the reasons behind the observed colors in both used and new oil. The scope includes concepts of thin film interference and light behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes the observation of colors in spilled oil and questions the reason behind it, considering that used oil is typically black.
  • Another participant suggests that thin film interference is the underlying phenomenon responsible for the colors observed in oil.
  • A further explanation is provided regarding how the crests and troughs of certain colors of light can cancel each other out, leading to the display of colors that are not canceled. This explanation is likened to the behavior of soap bubbles.
  • Participants discuss the relationship between film thickness, angle of light, and wavelength, indicating that these factors influence whether light waves undergo constructive or destructive interference.
  • There is a question about whether the same phenomenon occurs in both new and old oil, to which a participant responds affirmatively.
  • Some participants reflect on their personal experiences with noticing the colors in oil, indicating a sense of curiosity about why this observation was not made earlier in life.

Areas of Agreement / Disagreement

Participants generally agree on the concept of thin film interference as the explanation for the observed colors in oil. However, there is no consensus on the nuances of the phenomenon or the reasons for individual experiences regarding the observation of colors.

Contextual Notes

Some participants express uncertainty about the details of the explanation regarding light interference and its relationship to oil, indicating a need for further clarification or correction of their understanding.

jos93344
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I noticed that when i was working on my car today that when i spilled oil on the ground in the sun it looked as if it had a bunch of colors in it. I know that used oil is black and black absorbs light. So why does it show all of these colors?
 
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Thin film interference.
 
The crests and troughs of certain colors of light cancel each other out, so the oil displays all the colors that aren't canceled out. I may have something wrong there but that was my understanding of it, same goes for soap bubbles if you were wondering about those too.

Also please correct me if I have said something wrong here.
 
Entropee said:
The crests and troughs of certain colors of light cancel each other out, so the oil displays all the colors that aren't canceled out. I may have something wrong there but that was my understanding of it, same goes for soap bubbles if you were wondering about those too.

Also please correct me if I have said something wrong here.
No, that's more or less the right idea. Wikipedia actually has a decent explanation:
http://en.wikipedia.org/wiki/Thin-film_interference
Much of the article might be a bit technical but the pictures should give a good idea of what's going on.

Basically, whenever you have a thin film of something like oil, light reflects off both the top surface and the bottom surface of the film. If you have a specific relationship between the thickness of the film, the angle of the incoming light rays, and the wavelength of the light, those two reflections will destructively interfere (cancel each other out). For a slightly different specific relationship of those three quantities, the two reflections will constructively interfere (add together to produce a stronger wave).

For any given film thickness and angle, certain wavelengths undergo constructive interference and others undergo destructive interference. The constructively interfering waves will have the strongest intensity when they get to your eyes, so they mainly determine the color you see.
 
So does it do the same thing for new oil and old oil?
 
Last edited:
Pretty much yes.
 
I just wonder why you didn't notice such thing until recently
I noticed early in my childhood
 
netheril96 said:
I just wonder why you didn't notice such thing until recently
I noticed early in my childhood

i did notice it a long time ago but, never thought to ask why it did it.
 

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