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Unpolarized light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. The intensity of light beyond B is found to be I 2 . Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be I 8 . The angle between polarizer A and C is : 45 degree. is the answer Please explain how ?

Unpolarized light of intensity I passes through an ideal polarizer A. Another identical polarizer B is placed behind A. The intensity of light beyond B is found to be I 2 . Now another identical polarizer C is placed between A and B. The intensity beyond B is now found to be I 8 . The angle between polarizer A and C is : 
 
45 degree. is the answer 
 
Please explain how ?
 

Grade:11

3 Answers

Amit
405 Points
5 years ago
A poloroid only allows waves that are parallel to its axis. Now considering symmetry half of the waves will be perpendicular to axis and half would be parallel .. hence after passing through poloroid A intensity becomes I°/2.. Now after passing through B it is given Intensity is I°/2 .. hence A and B are parallel .. Now after placing C intensity after passing through C will be I°/2(cos²x) where x is angle between A and C .. now A and B are parallel hence intensity after passing through B intensity will be I°/2(cos²x)(cos²x).. it is equal to I°/8.. solve for x to get it π/4..
Amit
405 Points
5 years ago
Hope you get it.. For any doubt please feel free to ask anytime in comments...Thanks and regards..Tushar.
Ilovemy Username
20 Points
5 years ago
use mallus law
i=i1cos^2(fi)
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