[The (Late...) Fourteenth Blog] Light Interference.

[Bubble Pop by Hyuna]
An appropriate song, given the topic of this blog post. I don't actually like this song, but I had to. Hehe.

And to start this off, I apologize for this blog being so late. >_< [Hopefully it won't happen again.]

Now for the actual post:

Here we have a lovely picture of a gigantic bubble. [And an excited (or frightened...) child standing there on the side. Haha.] My friends took it when they went to the Children's Discovery Center way back when in...eighth grade.


As you can see, not only is the bubble enormous, but it is also adorned with pretty, shiny colors. Now, prior to being in physics class, I would see the colors and be captivated by them but not give them a second thought. I had no reason to know why they were there or how I could see them - they just were and I just could. [I never have been a very curious child...] But now I am able to explain to you the physics behind the appearance of those colors [or so I hope]. 


This color-producing phenomenon is known as thin film interference. When a beam of light travels from the air to the thin layer surrounding the bubble, it is reflected off of both the outer and inner surfaces of the bubble. When light rays are transmitted through the film before being reflected off of the inner surface, they travel a farther distance than rays reflected directly off the outer surface, resulting in a difference in wavelength between the two reflected beams. These beams interfere with each other, both constructively and destructively, resulting in the display of colors that we see. If the wavelengths are in phase, then constructive interference occurs and the color of that particular wavelength is reinforced. If the wavelengths are out of phase, the opposite holds true - destructive interference occurs and the color of that wavelength is destroyed. The colors that are seen are very much dependent upon the thickness of the film, given by the equations 2nt = mλ (constructive) and 2nt = (m+1/2)λ (destructive). With thicker films, longer wavelength colors (red) are cancelled out and blue-green colors can be seen, but as the film gets thinner, the shorter blue-green wavelengths cancel and yellow hues are more prominent. Eventually the film gets to be so thin that no colors can be seen and then pop! the bubble is gone. But it makes for a pretty sight while it lasts. :]