Question
  1. Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.
  2. The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index $\frac{3}{2},$ placed in water of refractive index $\frac{4}{3}.$ Will this ray suffer total internal reflection on striking the face AC? Justify your answer.

Answer

  1.  

When unpolarised light ray is incident at an angle such that the angle between reflected of refracted rays is 90°, then reflected ray is linearly polarised. In that case incident angle is called polarising angle or Brewster angle(iP or iB).

  1. For Total internal reflection $\Big(\frac{1}{\sin\text{i}_{\text{c}}}=\mu_{\text{DR}}\Big)$

$\sin\text{i}_{\text{c}}=\Big(\frac{1}{\sin\text{i}_{\text{c}}}=\mu_{\text{DR}}\Big)$

$\sin\text{i}_{\text{c}}=\mu_{\text{wg}}$

$\sin\text{i}_{\text{c}}=\frac{4}{3}\div\frac{3}{2}$

$=\frac{4}{3}\times\frac{2}{3}$

$\sin\text{i}_{\text{c}}=\frac{8}{9}=0.88$

Now, in this case

$\sin\text{i}=\sin60^\circ=\frac{\sqrt{3}}{2}=0.867$

$\because\ \sin\text{i}<\sin\text{i}_{\text{c}}$

$\text{So,}\ \text{i}<\text{i}_{\text{c}}$

So, ray will not suffer Total internal reflection.

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