Polarization

Two polaroid sheets are used with an overhead projector show how light is polarized. Light passing through the first polaroid sheet is polarized in a plane. When a second polaroid sheet in place on top and rotated the light is blocked when the polarization angles of the two sheets are perpendicular. Place a third piece of polaroid sheet between the cross polarized sheets and rotate this sheet at forty five degree relative to either of the first two sheets. Light is now transmitted.