An unpolarized light of certain intensity passes through a combination of two polarizers whose transmission axes are at 30° and 90°, respectively, with respect to the horizontal axis. A third polarizer with its transmission axis at 60° with the horizontal axis is placed between the two existing polarizers. The ratio of the output intensities with and without the third polarizer is .
- 3/4
- 4/3
- 9/4
- 4/9
Answer
(3) 9/4
Solution
After the first polarizer: I02 (unpolarized light is halved)
[figure]
Without the third polarizer, angle between P1 and P2 =60 :
I= I02 2 60 = I02 14= I08
With P3: angle P1 P3=30 and P3 P2=30
I'= I02 2 30 2 30 = I02 34 34= 9I032
I'I= 9/321/8= 94
Answer: (3)