Double Refraction in Calcite, 6H35.15
Topic and Concept:
Birefringence, 6H35. Birefringence
Location:
Cabinet: Optics (OP)
Bay: (A2)
Shelf: #1
Abstract:
Rotate crystal of calcite (also known as Iceland Spar) above printed text. Two images are visible; one remains fixed as the crystal is rotated, the other circumnavigates the first.
In the above left picture, see the "S" in "Spar" forms two images, which lie on a diagonal line running from upper left to lower right.
In the above right picture, the two images of the "S" now lie on a diagonal line running from upper right to lower left.
The fixed image is due to the so-called "ordinary" ray. The mobile image is due to the so-called "extraordinary" ray. (It's not easy to tell in the above pictures which image is fixed and which is mobile).
If a linear polarizer is available, it can be used to show that each ray is polarized, and that the angles of polarization of the two rays differ by 90°.
Equipment |
Location |
ID Number |
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Calcite crystal |
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Linear Polarizer |
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Discussion:
The mathematical description of birefringence seems too advanced for an introductory course, however the demonstration may catch students' interest.
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