An unpolarised light is successively passed through two polaroids .Their transmission axis make 60 degree with each other. If intensity of unpolarised light be I ,then intensity after second polariser is 
1) I/2
2) I/4
3) I/ 8
4) I/3
Please explain in detail.


Asked by Kb Aulakh | 25th Apr, 2015, 06:18: PM

Expert Answer:

Let the intensity of the incident unpolarised light be I
 
begin mathsize 12px style If space straight I subscript 1 space is space the space intensity space of space light space on space being space transmitted space from space the space first space polaroid comma then Accoeding space to space Malus space law space we space know space that colon straight I subscript 1 space equals straight I space cos squared space straight theta As space the space incident space light space is space unpolarised comma space the space intensity space of space the space light on space being space transmitted space from space the space first space polaroid space will space become colon straight I subscript 1 space equals space straight I over 2 Let space straight I subscript 2 space be space the space intensity space of space light space being space transmitted space through space the space second space polaroid colon Therefore space colon straight I subscript 2 space equals space straight I subscript 1 space cos squared space straight theta straight I subscript 2 space equals space straight I over 2 space cos squared space straight theta Given space straight theta space equals space 60 straight I subscript 2 space equals space straight I over 2 space cos squared space 60 straight I subscript 2 space equals space straight I over 2 space cross times 1 fourth straight I subscript 2 space equals straight I over 8 end style
Therefore the  intensity after second polariser is I/8
Correct option is 3) I /8

Answered by Jyothi Nair | 27th Apr, 2015, 09:43: AM