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  • (a) Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface. (b) The figure shows a ray of light falling normally on the face AB of an equilateral glass prism havin

(a) Show using a proper diagram how unpolarised light can be linearly
polarised by reflection from a transparent glass surface.
(b) 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.
  

 

 

 
 
 
 
 

Answers (1)

a)
 
         When unpolarized light is linearly polarised by reflection the amount of polarisation depends upon the incident angle. At a particular angle (Brewster angle) the polarisation of reflected light is maximum.
Polarisation by Reflection is explained by Brewester's law which states that the tangent of polarising angle is equal to the refractive index of the medium. Moreover refracted and reflected rays are perpendicular.
 \tan i_{p}= \mu

b)
  
Given that,
            the refractive index of the glass prism = \frac{3}{2}
            the refractive index of water = \frac{4}{3}
From figure the angle of incidence of the ray on the face AC is 60^{\circ}= i
The total internal reflection takes place only when the angle of incidence is greater than the critical angle ic.
Here relative refractive index of glass

\mu = \frac{\frac{3}{2}}{\frac{4}{3}}= \frac{9}{8}
condition for total internal reflection is

\sin i_{c}= \frac{1}{\mu }
= \frac{1}{\frac{9}{8}}= \frac{8}{9}= 0\cdot 89
Therefore critical angle

\sin i_{c}=\sin^{-1}\left ( 0\cdot 89 \right )= 62\cdot 73^{\circ}
Since the critical angle is greater than the incident angle, the total internal reflection will not the place.

Posted by

Safeer PP

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