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  4. If the critical angle for total internal reflection from a medium to vacuum is 45°, then velocity of light in the medium is,

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Q. If the critical angle for total internal reflection from a medium to vacuum is $45^{\circ}$, then velocity of light in the medium is,

NEETNEET 2020Ray Optics and Optical Instruments

Solution:

$sin\,\theta_{C}=\frac{1}{\mu}$
$\mu=\frac{1}{sin\,\theta_{c}}$
$=\frac{1}{sin\,45^{\circ}}$
$=\frac{1}{\left(1/\sqrt{2}\right)}=\sqrt{2}$
$\mu=\frac{C}{V} \Rightarrow V =\frac{C}{\mu}$
$=\frac{3\times10^{8}}{\sqrt{2}} m/ sec$