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||<30%  style="text-align:center">[[PiraScheme#Optics|Table of Optics Demonstration]] ||<30%  style="text-align:center">[[OPEquipmentList|List of Optics Equipment & Supplies]] ||<30%  style="text-align:center">[[Demonstrations|Lecture Demonstrations]] ||


= Double Refraction in Calcite, 6H35.15 =
'''Topic and Concept:'''

 . Birefringence, [[Polarization#Birefringence|6H35. Birefringence]]

'''Location:'''

 * '''Cabinet:''' [[Optics|Optics (OP)]]
 * '''Bay:''' [[OpticsCabinetBayA2|(A2)]]
 * '''Shelf:''' #1
 {{attachment:CalciteView1A.jpg}} {{attachment:CalciteView1PlusPiOver2A.jpg}}

'''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°.

||<40%  style="text-align:center">'''Equipment''' ||<30%  style="text-align:center">'''Location''' ||<25%  style="text-align:center">'''ID Number''' ||
|| || || ||
||Calcite crystal ||[[OpticsCabinetBayA2|OP, Bay A2, Shelf #1]] || ||
||Linear Polarizer ||[[OpticsCabinetBayB5|OP, Bay B5, Shelf #2]] || ||



'''Discussion:'''

The mathematical description of birefringence seems too advanced for an introductory course, however the demonstration may catch students' interest. 



'''Videos:'''

 * [[https://www.youtube.com/user/LectureDemostrations/videos?view=1|Lecture Demonstration's Youtube Channel]]

'''References:'''

 * Hyperphysics  http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/biref.html

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