What is the principle used in the working of 3D glasses?
3D glasses are actually polaroids. They are not creating the 3D effects. The 3 D movies are filmatographed with two cameras help at two different angles just like we see with TWO eyes.
The two films are projected on the screen with polarized light with their plane of polarization in perpendicular to each other. If we look at the screen without ant 3D glass we will see blurred images only as the two pictures are overlapping each other and both the image are seen together by both the eyes.
3D glasses use Polaroid with the plane of polarization in mutually perpendicular directions. So, when we wear the Polaroid glasses and look at the screen, only one of the image will be seen by one of the eyes and the second eye sees the other image. This creates the 3D sensation, we are seeing the image filmed with the left camera with the left aye and that with the right camera with right eye.