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Wave Optics — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsWave Optics3 Marks
Question
  1. Show, giving a suitable diagram, how unpolarized light can be polarised by reflection.
  2. Two polaroids $P_1$ and $P_2$  are placed with their pass axes perpendicular to each other. Unpolarised light of intensity $I_o$ is incident on $P_1$ A third polaroid $P_3$ is kept in between $P_1$ and $P_2$ such that its pass axis makes an angle of $60^{\circ}$with that of $P_1$. Determine the intensity of light transmitted through $P_1$, $P_2$ and $P_3$.
✓

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, $i_p,$ where \tan $i_p = \mu$
  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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