Light is defined in previous article However, a wave is free to oscillate right and left or up and down or at any angle between the vertical and horizontal. Some kinds of crystals have a special property of polarizing light, meaning that they force light to oscillate only in the direction in which the crystals are aligned. We find this property in the crystals in Polaroid disks.In other words the two interfering waves must be same state.
The human eye can’t tell the difference between a polarized beam of light and one that has not been polarized. However, if polarized light passes through a second Polaroid disk, the light will be dimmed the more that second disk is out of alignment with the first. For instance, if the first disk is aligned vertically and the second disk is aligned horizontally, no light will pass through. If the second disk is aligned at a 45ºangle to the vertical, half the light will pass through. If the second disk is also aligned vertically, all the light will pass through