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(i) 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. 

(ii) 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 poiaroid B reduces to 1/8th of the intensity of unpolarised light incident on A ?

1 Answer

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Best answer

(i) 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 an unpolarised light is incident on a transparent surface, the reflected light gets partially or completely polarised/ the reflected light gets completely polarised when the reflected and refracted light are perpendicular to each other.

(ii) Let θ be the angle between the pass-axis of A and C.

Intensity of light passing through A = I0/2

Intensity of light passing through C = (I0/2) cos2θ

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