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(a) How does an unpolarised light incident on a polaroid get polarised ? Describe briefly, with the help of a necessary diagram, the polarisation of light by reflection from a transparent medium. (b) Two polaroids 'A' and 'B' are kept in crossed position. How should a third polaroid 'C' be placed between them so that the intensity of polarised light transmitted by polaroid B reduces to 1/8 th of the intensity of unpolarised light incident on A? |
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Answer» Solution :The third polaroid, C, should be placed at an angle of `45^@` with pass axis of POLARISER A, therefore, `I_A = I_0 cos^2 45^@` (Intensity of LIGHT coming from A). `I_A = (I_0)/2` `I_C = (I_0)/2 cos^2 45^@` (Intensity of light coming from polaroid) `=(I_0)/2 (1/(sqrt2))^2 = (I_0)/4` `I_B = (I_0)/4 cos^2 45^@` (Intensity of light coming from polaroid B) `= (I_0)/4 (1/(sqrt2))^(2) = (I_0)/8` Hence, the polaroid C should be at an angle of `45^@` with polaroid A. |
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