The Phenomenon of Refraction: Understanding the Disappearing Glass
Isabelle Morris
Award: Top 100
School: concord college
Teacher: bart wargos
Category: Contrived
Photo #19392
The Phenomenon of Refraction: Understanding the Disappearing Glass
In this demonstration, we observe two glass test tubes placed inside a glass cylinder. The test tube on the right is filled with corn oil, while the test tube on the left is empty and contains air. The right test tube appears nearly invisible due to the similarity in refractive indices between glass and corn oil. Glass has a refractive index of 1.5, and corn oil has a slightly lower refractive index of 1.48. This close alignment means that light passes through both materials with minimal bending, making it difficult for the human eye to detect the boundary between them. As a result, the test tube filled with corn oil effectively blends in with its surroundings.
Conversely, the left test tube, which is filled with air, is visible. Air has a significantly lower refractive index of 1.0003 compared to glass. This disparity causes light to bend and reflect at the boundary where glass meets air, creating a noticeable outline of the test tube. Therefore, the difference in refractive indices is key to why the empty test tube stands out, allowing for clear visibility.
The concept relates to H.G. Wells' story 'The Invisible Man, ' which explores the problems of a man who is precisely that. His refractive index would be equal to that of the air around him. Otherwise, refraction effects would slightly bend rays passing through him, leading to minor distortion effects in the image of objects seen through the man.
Detection by the retina implies that light energy is absorbed, so someone looking through the back of the invisible man's head would be able to detect the loss of energy where the light energy was absorbed – it's still a good story, though!
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