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State clearly how an unpolarised light gets linearly polarised when passed through a polaroid. (i) Unpolarised light of intensity I_(0) is incident on a polaroid P_(1) which is kept near another polaroid P_(2) whose pass axis is parallel to that of P_(1). how will the intensities of light, I_(1) and I_(2), transmitted by the polaroids P_(1) and P_(2) respectively, change on rotating P_(1) without disturbing P_(2) ? (ii) Write the relation between the intensities I_(1) and I_(2). |
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Answer» <P> Solution :For obtaining linearly polarised light on passing unpolarised light through a polaroid.(i) Let unpolarised light of intensity `I_(0)` is incident on a polaroid `P_(1)` then intensity of plane polarised light TRANSMITTED by polaroid `P_(1)` is `I_(1)=(I_(0))/(2)` As pass axis of polaroid `P_(2)` is parallel to that of `P_(1)`, hence intensity of light transmitted by polaroid `P_(2)` is `I_(2)=I_(1)=(I_(0))/(2)`. However, if the polaroid `P_(1)` is rotated about its axis and the pass axis of `P_(1)` SUBTENDS an angle `theta` with pass axis of `P_(2)`, then `I_(1)=(I_(0))/(2)` but `I_(2)=I_(1)cos^(2)theta=(I_(0))/(2)cos^(2)theta.` If `theta=90^(@)`, then `I_(2)=(I_(0))/(2)cos^(2)(90^(@))=0`. (ii) The relation between `I_(1) and I_(2)` is GIVEN as: `I_(2)=I_(1)cos^(2)theta`, where `theta` is the angle between the pass axes of two polaroids. |
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