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CBSE Class 12-science Answered

Between two polaroids placed in crossed position a third polaroid is introduced.The axis of the third polaroid makes an angle of 30 degree with the axis of the first polaroid. find the intensity of transmitted light from the system assuming Io to be the intensity of polarised light on the first polaroid.
Asked by Rajeev | 21 Feb, 2016, 11:25: PM
answered-by-expert Expert Answer
The third polaroid inserted between the first and second is at an angle of 30° with the first.
So, the intensity of light transmitted from the third polariser is given from Malus' law as

begin mathsize 14px style straight I subscript 3 equals straight I subscript 0 cos squared 30 therefore straight I subscript 3 equals straight I subscript 0 open parentheses fraction numerator square root of 3 over denominator 2 end fraction close parentheses squared therefore straight I subscript 3 equals fraction numerator 3 straight I subscript 0 over denominator 4 end fraction end style
 
Now, it is given that initially the first and second polaroids are in crossed position.
Therefore, the angle between them is 90°.
Now, the third polaroid in between is at an angle 30° from first. So, the angle between the third and second is 60°.
 
Therefore, the final intensity from second polaroid is
 
begin mathsize 14px style straight I subscript 2 equals straight I subscript 3 cos squared 60 therefore straight I subscript 2 equals fraction numerator 3 straight I subscript 0 over denominator 4 end fraction cross times open parentheses 1 half close parentheses squared therefore straight I subscript 2 equals fraction numerator 3 straight I subscript 0 over denominator 16 end fraction end style
Answered by Romal Bhansali | 22 Feb, 2016, 11:16: AM
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