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(a) How dpes an unpolarized light incident on a polaroid get polarized? Describe briefly with the help of a necessary diagram the polarization 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 polarized light transmitted by polaroid B reduces to 1//8^(th) of the intensity of unpolarized light incident on A ? |
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Answer» Solution :(a) When an unpolarised light falls on a polaroid, it lets only those of its ELECTRIC vectors that are oscillating along a direction perpendicular to its aligned molecules to pass through it. The incident light thus gets linearly polarised. Alternatively,  WHENEVER unpolarised light is incident on a transparent surface, the reflected light gets partially or completely polarized/the reflected light gets completely polarized when the reflected and refracted light are perpendicular to each other. (b) Let `theta` be the angle between the pass axis of A and C Intensity of light passing through `A=(I_(0))/(2)` Intensity of light passing through`C=((I_(0))/(2))cos^(2)theta` Intensity of light passing through B `=((I_(0))/(2))cos^(2)theta.[cos^(2)(90-theta)]` `implies(I_(0))/(2)xx(SIN^(2)theta)/(4)=(I_(0))/(8)` (Given) `:.sin2theta=1` `2theta=90^(@)` The third polaroid is placed at `theta=45^(@)` |
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