Crossed polarizers are best described as what?

• A. Two polarizers with their light-transmitting directions aligned perpendicularly so light cannot transmit through them
• B. A pair of analyzers oriented at 90 degrees to each other that block light
• C. A color filter for gemstones
• D. A method to measure refractive index by stress

Answer: (A)

Crossed polarizers mean two polarizing filters with their transmission directions at right angles to each other. The first polarizer makes light linearly polarized, and the second, oriented 90 degrees to it, blocks that polarized light, so little or no light gets through. This extinction is the defining feature. In gem testing, this setup helps reveal birefringence and interference colors in transparent stones, because anisotropic materials can alter polarization enough that some light gets through the second polarizer, producing observable effects.