Two polarizing filters have their transmission axes crossed at so that zero light is transmitted. When a third polarizer is inserted between them with its transmission axis oriented at to both, what fraction of incident unpolarized light of intensity emerges from the combination?

Answer and explanation

Correct answer: B.

  1. Step 1: After the first polarizer, intensity is polarized along .
  2. Step 2: The second polarizer is at : .
  3. Step 3: The third polarizer is at , which is at relative to the second: .
Answer
.
Why not the others: Zero assumes the middle polarizer has no effect (ignoring state projection); omits the first or last projection step; squares the transmission twice.

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