Question

The refractive index of glass is 1.5 and that of water is 1.3. If the speed of light in water is $2.25\times {10}^{8}m{s}^{-1}$, what is the speed of light in glass?

Answer 1

We know that refractive index of medium is $n=\frac{speedoflightinvaccum}{speedoflightinvacuum}$

$n=\frac{c}{v}$ ,

c is the velocity of light in vacuum and v is velocity in that medium.

For water :

$n=\frac{c}{v}$

$1.3=\frac{c}{2.25\times {10}^8}$

$c=2.925\times {10}^{8}m/s$

For glass :

$c=2.925\times {10}^{8}m/s$

$n_{glass}=\frac{c}{v_{glass}}$

$1.5=\frac{2.925\times {10}^8}{v_{glass}}$

$v_{glass}=1.95\times {10}^{8}m/s$