What is the direction (vertical or horizontal) of the transmission axis of Polaroid sunglasses? Give the physical reason for your answer.

Sunglasses are vertically polarized. This enables them to greatly suppress or block obliquely reflected light ("glare") from horizontal surfaces like bodies of water or car hoods, which is mostly horizontally polarized.

See http://www.polarization.com/water/water.html

The direction of the transmission axis of Polaroid sunglasses is usually vertical.

To understand why, let's first explain how Polaroid sunglasses work. Polaroid sunglasses have a special coating that contains microscopic vertical chains or crystals that act as a polarizer. These chains or crystals only allow light waves that vibrate in a specific orientation to pass through, blocking most of the glare from horizontally polarized light.

Now, when we wear sunglasses, we mainly want to block out horizontally polarized light, which is responsible for the glare we often encounter from surfaces such as water, roads, or shiny objects. By having the transmission axis of the sunglasses vertically oriented, they effectively block horizontally polarized light. This blocking reduces the intensity of the glare and improves our vision, allowing us to see more clearly and comfortably.

So, to answer your question, the transmission axis of Polaroid sunglasses is usually vertical because vertical transmission axis effectively blocks horizontally polarized light, which is the main source of glare that we want to eliminate.