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EEJ MAIN Physics QUESTION #7023
Question 1
Unpolarized light passes through polarizer A, then B, resulting in half the initial intensity. If a third polarizer C is placed between them, the final intensity drops to $\frac{1}{8}$ of the original. What is the angle between polarizer A and C?
  • $45^\circ$✔️
  • $60^\circ$
  • $0^\circ$
  • $30^\circ$
Correct Answer Explanation

Initial intensity $I$. After A, $I_A = I/2$. Since $I_B$ is also $I/2$, axes of A and B are parallel ($\theta_{AB} = 0$).

Insert C at angle $\phi$ to A. Then angle between C and B is also $\phi$.

Final intensity $I' = I_A \cos^2 \phi \cos^2 \phi = \frac{I}{2} \cos^4 \phi$.

Given $\frac{I}{2} \cos^4 \phi = \frac{I}{8} \implies \cos^4 \phi = \frac{1}{4} \implies \cos^2 \phi = \frac{1}{2}$.

Thus, $\cos \phi = \frac{1}{\sqrt{2}} \implies \phi = 45^\circ$.