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Size: 2429
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| A sample of glass (or possibly polymeric) spheres collected from University Ave. outside Chamberlin Hall following the painting of the crosswalks. Typical sphere diameter 400 microns. | A sample of glass (or possibly polymeric) spheres collected from University Ave. outside Chamberlin Hall following the painting of the crosswalks. Typical sphere diameter 400 microns. |
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| '''''Important Setup Notes:''''' * ''''' ''''' |
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| 1. List steps for setup then procedure. 1. ... |
Darken room except for single spotlight. Place large sheet of white paper below spotlight, empty spheres on paper, and spread them out so that paper is more or less evenly covered. Stand so that shadow of head falls in center of paper. Observe colored halo surrounding head. {{attachment:Halo.jpg||font-size="1em"}} |
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| Discuss the physics behind the demonstration, explaining some of the various steps of the demonstration when appropriate. || {{attachment:Halo.jpg}} || |
Small spheres are excellent retroreflectors--that's why transportation engineers embed them in paint used to mark roads. |
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| The exact size of "small" depends on the index of refraction. | |
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| This is an example of Mie scattering. | |
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| One way to motivate an interest in Mie scattering (which is an advanced topic): when sunlight illuminates falling spherical raindrops, the result is a rainbow. However, clouds are made of more or less spherical droplets of water. Why do we not see a rainbow every time there is a cloud? The answer turns out to be that there is a significant difference between the scattering of light by drops of about 300 |
Rainbow Dust, 6A46.16
Topic and Concept:
Geometrical Optics, 6A46. Rainbow
Location:
Cabinet: Optics (OP)
Bay: (A2)
Shelf: #1
Abstract:
A sample of glass (or possibly polymeric) spheres collected from University Ave. outside Chamberlin Hall following the painting of the crosswalks. Typical sphere diameter 400 microns.
Equipment |
Location |
ID Number |
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Rainbow Dust |
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Setup and Procedure:
Darken room except for single spotlight.
Place large sheet of white paper below spotlight, empty spheres on paper, and spread them out so that paper is more or less evenly covered.
Stand so that shadow of head falls in center of paper.
Observe colored halo surrounding head.
Discussion:
Small spheres are excellent retroreflectors--that's why transportation engineers embed them in paint used to mark roads.
The exact size of "small" depends on the index of refraction.
This is an example of Mie scattering.
One way to motivate an interest in Mie scattering (which is an advanced topic): when sunlight illuminates falling spherical raindrops, the result is a rainbow.
However, clouds are made of more or less spherical droplets of water. Why do we not see a rainbow every time there is a cloud?
The answer turns out to be that there is a significant difference between the scattering of light by drops of about 300
Videos:
References:
From the transportation engineer's point of view: http://www.dot.state.fl.us/construction/Engineers/MOT/Presents/PavementMarkingTraining.pdf