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Wave Optics — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsWave Optics3 Marks
Question
  1. Show, giving a suitable diagram, how unpolarized light can be polarised by reflection.
  2. Two polaroids P1 and P2  are placed with their pass axes perpendicular to each other. Unpolarised light of intensity Io is incident on P1 A third polaroid P3 is kept in between P1 and P2 such that its pass axis makes an angle of $60^{\circ}$with that of P1. Determine the intensity of light transmitted through P1, P2 and P3.
✓

Answer

  1. When unpolarised light is incident on the boundary between two transparent media, the reflected light gets plane polarized with its electric vector perpendicular to the plane of incidence.

The polarization is complete when the reflected and refracted rays are at right angles to each other. This condition occurs for an angle of incidence, ip, where tan ip = $\mu$

  1. Intensity of light through $\text{P}_1=\frac{I_0}{2}$

Intensity of light through $\text{P}_2=\frac{I_0}{2}\cos^260$

$\frac{I_0}{2}.\bigg(\frac{1}{2}\bigg)^2=\frac{I_0}{8}$

Intensity of light through $ \text{P}_3=\frac{I_0}{8}\cos^230=\frac{I_0}{8}\times\bigg(\frac{\sqrt{3}}{2}\bigg)^2=\frac{3I_0}{32}$

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