CBSE Class 12 · 2017 · Delhi · Wave OpticsLong Answer

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(a) Distinguish between unpolarized light and linearly polarized light. How does one get linearly polarised light with the help of a Polaroid?
(b) A narrow beam of unpolarised light of intensity

I_{0}

is incident on a Polaroid

P_{1}

. The light transmitted by it is then incident on a second Polaroid

P_{2}

with its pass axis making an angle of

6 0^{\circ}

relative to the pass axis of

P_{1}

. Find the intensity of the light transmitted by

P_{2}

Solution

(a) In

unpolarised light

the electric-field oscillations are in random directions in the plane perpendicular to propagation; in

linearly polarised light

they are confined to one direction. When unpolarised light passes through a polaroid, the component of the field parallel to the aligned molecules is absorbed and only the component along the pass axis is transmitted, so the emergent light is linearly polarised.
(b) After

P_{1}

I_{1} = \frac{I _{0}}{2}

. By Malus' law at

P_{2}

(

θ = 6 0^{\circ}

I = I_{1} cos^{2} 6 0^{\circ} = \frac{I _{0}}{2} (\frac{1}{2})^{2} = \frac{I _{0}}{8}

I = \frac{I _{0}}{8}

CBSE Class 12 Board · 2017 · Delhi · Subjective

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CBSE Class 12 · 2017 · Delhi · Wave OpticsLong Answer

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