Question

Light ray is travelling from a denser medium into a rarer medium. The velocity of light in the denser and rarer medium is $2\times {10}^8$ m/sec. and $2.5\times {10}^8$ m/sec. The critical angle of the two media is :

• A. sin${}^{-1}$ (5/4)
• B. sin${}^{-1}$(4/5)
• C. sin${}^{-1}$ (2/3)
• D. sin${}^{-1}$(5/6)

Answer 1

Answer: (B)

sin${}^{-1}$(4/5)

$\frac{v=2.5\times {10}^8\left(rarer\right)}{v=2\times {10}^8\left(denser\right)}=\mu =\frac{2.5\times {10}^8}{2\times {10}^8}=\frac{5}{4}$

${\theta }_{cric}=si{n}^{-1}\left(\frac{1}{\mu }\right)=si{n}^{-1}\left(4/5\right)$