Answer to Question #193 in Optics for jolisa
A quartz plate, which is 1mm thick, is cut perpendicular to the optical axis. How to determine from which quartz - the right- or levogyrate – the plate is made, having before two nicoles and the source of: 1) monochromatic light; 2) white light?
1) If you put a plate of quartz, which is cut perpendicular to the optical axis, between crossed nicoles, and light the system with monochromatic light, it will let in the light; turning the analyzer to an angle less than 90º, you can turn out the light. If the observer has to rotate the analyzer clockwise, then the quartz will be dextrogyrate, if counterclockwise, then it is levogyrate.
2) If you light the system with white light, then the plate will seem colored. Rotational capacity increases with the decrease of wavelength. Therefore, if the analyzer is rotated in a clockwise direction, then for the dextrorotatory quartz the color will change in the direction of shorter wavelengths of the spectrum. For the levogyrate quartz the order of coloring change will be otherwise.
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