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An unpolarised beam of light of intensity l_0 falls on a poloroid. The intensity of the emergent beam is |
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Answer» `I_0/2` `I_0 prop E_0^2`………..(1) Intensity of transmitted light with amplitude `E_0 cos theta` (where `theta`= angle made by incident `vec E` VECTOR with the optic (or pass) axis of a given POLOROID) is, `I prop (E_0 cos theta)^2` `therefore I prop E_2^ cos^2 theta`..........(2) TAKING ratio of equation (2) to equation (1) Now, intensity of transmitted beam is the average of above intensity, Hence, `lt I gt =I_0lt cos^2 theta gt `( `because I_0`= constant) `therefore lt I gt =I_0(1/2)` (`because` Incident light in unpolarised and so `theta` varies between 0 to `2pi` and we know average value of `cos^2 theta` over this interval is `1/2`) `therefore lt I gt =I_0/2` |
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