Plane-Polarized Light and 3-D Movies

We see in three dimensions because our eyes view the world ftom slightly different positions. Our brains synthesize a three-dimensional (3-D) picture based on the two different pictures sent to it by our eyes. Modem 3-D movies make use of this phenomenon to make it seem as though objects on the screen ate actually moving toward the viewer. 

Three-dimensional movies are filmed using two different cameras at slightly different angles to the action. Thus, there are actually two movies that must be shown to us simultaneously. To make sure that our two eyes receive two different perspectives, each movie is projected through a polarizer, which polarizes the two projections in directions perpendicular to each other (Figiue 10.6). 

If we were to watch the movie without the special glasses provided by the movie house, we would see the blurry combination of the two movies. However, the 3-D glasses consist of polarized lenses, with planes of polarization that ate mutually perpendicular. The left lens, polarized in one direction, blocks the image that is polarized perpendicular to it. The right lens, polarized in the other direction, blocks the other image. Oiu eyes are tricked into seeing two different movies, which our brain combines to form one 3-D image. The results of this process can be quite impressive  

Another example of chiral switching is that of the selective serotonin reuptake inhibitor (SSRI) antidepressant Celexa, which was introduced to the market in 1998 by Forest Laboratories. Celexa is a racemic mixture of (i )-citalopram oxalate and (5)-citalopram oxalate. While orrly the (S) enantiomer has therapeutic antidepressant properties, both enantiomers contribute to the side effects of the drug and therefore limit effectiveness and patient tolerance. In 2002, the FDA approved Lexapro, a new antidepressant derived from Celexa but from which the therapeutically ineffective (R) enantiomer has been removed. The benefits of isolating the active isomer include smaller required dosages, reduced side effects, and a faster and better patient response to the drag. 

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