Optics > Polarization > Birefringence DCS# 6H35.50
STRESS BIREFRINGENCE
APPARATUS
two polarizers 202-21-E6
overhead projector 200
plastic protractor, fork
 101-34-D2
plexiglass disk or cube with C-clamp
 202-18-D6
strained glass in plastic mount 202-21-E6
plastic punch bowl
 108A
piece of glad wrap 202-02-G2
DESCRIPTION
Show various clear plastic objects between crossed polarizers on the overhead projector.  When flexed the plastic becomes anisotropic and therefore birefringent and bands of color can be seen.  The protractor shows colored bands without being deformed because anisotropies arise when the plastic solidifies when manufactured.  The colored patterns reveal internal stresses.
protractor between crossed polarizers
Place saran wrap between crossed polarizers and stretch along a direction 45° to the polarization axes to show that it becomes birefringent and allows a component of the light to pass.


NOTES
 
We have a commercial device (202-21-E6)  to do the squeezing and stretching of the items in the polaroid specimens kit.