Polaroid Sheets
Purpose
Polaroid sheets on an overhead projector demonstrate Malus's Law and the three-polarizer paradox. Students observe crossed polarizers blocking light, then see that inserting a third polarizer at 45° between them restores partial transmission.
Figure 1:
Setup showing the ring stand with a ring holding the upper polaroid sheet above the lower sheet on the masked overhead projector stage. Rotating the ring rotates the upper polarizer.
Figure 2:
Parallel polarizers: near-maximum transmission. The bright stripe at the right edge is light passing outside the upper polarizer through the mask opening.
Figure 3:
Crossed polarizers at 90°: nearly all light is blocked. The remaining bright strip is light passing outside the overlap region of the two polarizers.
Figure 4:
Third polarizer at 45° inserted between crossed polarizers restores partial transmission. The bright region shows where the intermediate polarizer changes the polarization state, allowing light through the analyzer.