A ray of light entering from air into a denser medium of refractive index 4/3, as shown in figure. The light ray suffers total internal reflection at the adjacent surface as shown. The maximum value of angle θ should be equal to :

 

<p>By shell's law<br> (sin θ)/ (sin θ') = 4/3 . (i)<br>For TIR on second surface<br>sin θ' &gt; sin θc<br> (θ' + θ' = 90)<br>sin (90 - θ') &gt; sin θc<br>cos θ' &gt; sin θc<br>1 - sin²θ' &gt; sin²θc (By equation (i) )<br>1 - (3/4 sin θ)² &gt; sin²θc<br> [sin θc = 3/4]<br>1 - (9/16)sin²θ &gt; (9/16)<br>1 - 9/16 &gt; (9/16)sin²θ<br>7/16 &gt; (9/16)sin²θ<br>sinθ &lt; √7/3</p>

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