question_answer

When a sheet of transparent plastic is placed between two crossed polarizers, no light is transmitted. When the sheet is stretched in one direction, some light passes through the crossed polarizers. What is happening?                             

Answer:

                A transparent plastic sheet is not a polaroid. So when two polaroids are placed with crossed axes, no light is transmitted, whether the plastic sheet is placed between them or not. But when the sheet is stretched, the polymer molecules in it make it a polaroid with its own polaroid axis, which may make some angle with the axes of the two polaroids. Now it becomes a case of three polaroids with the middle polaroid having its axis between the axes of the two fixed polaroids. That is why some light is transmitted in this case.