Question

The refractive index of water is $\frac{4}{3}$. The speed of light in water is:

(Take the speed of light in air $=3\times {10}^{8}m{s}^{-1}$)

• A. $2\times {10}^{8}m{s}^{-1}$
• B. $2.25\times {10}^{8}m{s}^{-1}$
• C. $3\times {10}^{8}m{s}^{-1}$
• D. $2.5\times {10}^{8}m{s}^{-1}$

Answer 1

The correct option is B $2.25\times {10}^{8}m{s}^{-1}$

Given:
Refractive index of water, $n=\frac{4}{3}$
Speed of light in air, $c=3\times {10}^{8}m{s}^{-1}$.

From definition of refractive index of a medium,
$n=\frac{c}{v}$
where:
$v:$ Speed of light in the medium

Substituting values, we get:
$\frac{4}{3}=\frac{3\times {10}^8}{v}$
$v=2.25\times {10}^{8}m{s}^{-1}$