Question

If the critical angle of the medium is ${30}^{\circ }$, the velocity of light in that medium is :
(velocity of light in air $3\times {10}^8$ m/s)

• A. $6\times {10}^{8}m/s$
• B. $3\times {10}^{8}m/s$
• C. $1.5\times {10}^{8}m/s$
• D. $1\times {10}^{8}m/s$

Answer 1

The correct option is C $1.5\times {10}^{8}m/s$

As, ${\theta }_{cric}=si{n}^{-1}\left(\frac{1}{\mu }\right)$

$sin{\theta }_{cric}=\frac{1}{\mu }$

$\mu =\frac{1}{sin30}=2$

Also as $\mu =\frac{c}{v_m}=\frac{3\times {10}^8}{v_m}$

$v_m=1.5\times {10}^{8}m/s.$