Question

If the critical angle for total internal reflection from a medium to vacuum is 30${}^o$, then velocity of light in medium will be:

• A. $1.5\times {10}^{8}m/s$
• B. $2\times {10}^{8}m/s$
• C. $3\times {10}^{8}m/s$
• D. $5\times {10}^{8}m/s$

Answer 1

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

Using Snell's law, $n\times sin{30}^o=1\times 1$

Therefore $n=\frac{1}{sin{30}^o}=2$

So, Velocity in the medium is, $v=\frac{c}{n}=3\times \frac{\left({10}^8\right)}{2}=1.5\times {10}^{8}m/s$