MCQ
With respect to air critical angle in a medium for light of red colour $\left[\lambda_1\right]$ is $\theta$. Other facts remaining same, critical angle for light of yellow colour $\left[\lambda_2\right]$ will be
  • A
    $\theta$
  • B
    More than $\theta$
  • Less than $\theta$
  • D
    $\frac{\theta \lambda_1}{\lambda_2}$

Answer

Correct option: C.
Less than $\theta$
$ \text { Critical angle }=\sin ^{-1}\left(\frac{1}{\mu}\right) $
$ \therefore \theta=\sin ^{-1}\left(\frac{1}{\mu_{\lambda_1}}\right) \text { and } \theta^{\prime}=\sin ^{-1}\left(\frac{1}{\mu_{\lambda_2}}\right)$
Since $\mu_{\lambda_2}>\mu_{\lambda_1}$, hence $\theta^{\prime}<\theta$

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