Q156 / 180 · KCET 2024 · Physics

Three polaroid sheets are co-axially placed as indicated in the diagram. Pass axes of the polaroids 2 and 3 make $30^{\circ}$ and $90^{\circ}$ with pass axis of polaroid sheet 1 . If $I_0$ is the intensity of the incident unpolarised light entering sheet 1 , the intensity of the emergent light through sheet 3 is Figure

  • Correct answer
    A
    zero
  • B
    $\frac{3 I_0}{32}$
  • C
    $\frac{3 I_0}{8}$
  • D
    $\frac{3 I_0}{16}$

Solution

Intensity of polarised light passing through first polaroid, $I_1=I_0 / 2$ Intensity of light passing through second polaroid, $I_2=I_1 \cos ^2 \theta$ $=\frac{I_0}{2} \cos ^2 30^{\circ}=\frac{3}{4} I_0$ Intensity of polarised light transmitted through third polaroid, $I_3=I_2 \cos ^2 \theta$ $=\frac{3}{4} I_0 \cos ^2 90^{\circ}$ $=\frac{3}{4} I_0 \times 0=0$

Hence, the correct answer is option: 'A'.

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