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A ray of light is incident from a denser to a rarer medium. The critical angle for total internal reflection is \Theta _{iC} and the Brewster’s angle of incidence is \Theta _{iB},  such that  \sin \Theta _{iC}/\sin \Theta _{iB}= \eta = 1.28.  The relative refractive index of the two media is :

 

Option: 1

0.2


Option: 2

0.4


Option: 3

0.8


Option: 4

0.9


Answers (1)

best_answer

\sin\theta _{ic}=\frac{\mu_ r}{\mu _d}

\mu_r = refractive index of the rarer medium.

\mu_d = refractive index of the rarer medium.

In the case of Brewster’s angle

r = 90-\theta _{iB}

From Brew's law: \mu _{d}.\sin\theta _{iB}=\mu _{r}.\sin r

\frac{\sin\theta _{iB}}{\cos\theta _{iB}}=\frac{\mu _{r}}{\mu _{d}}  or \tan\theta _{iB}=\frac{\mu _{r}}{\mu _{d}}

\sin\theta _{iB}= \frac{\mu _{r}}{\sqrt{\mu _{r}^{2}+\mu _{d}^{2}}}....(2)

\because\frac{ \sin\theta _{ic}}{ \sin\theta _{iB}}=1.28

\mu _{1}^{2}+\mu _{d}^{2}=1.638\mu _d^{2} 

or \ \ 0.638\mu d^{2}=\mu _{r}^{2}

\frac{\mu _{r}}{\mu _{d}}=\sqrt{0.638}=0.8

 

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manish

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