Question

The refractive index of water is $1.33 .$ The speed of light in water is :

• A. $1.33 \times 10^{8} \,m / s$
• B. $4 \times 10^{8} \,m / s$
• C. $2.25 \times 10^{8} m / s$
• D. $3 \times 10^{8} m / s$

Answer 1

Answer: (C)

Water is a denser medium compared to air.
From Huygen's wave theory, we have
${ }_{1} n_{2}=\frac{v_{1}}{v_{2}}=\frac{\text { Speed of light in first medium }}{\text { Speed of light in second medium }}$
Given, $_{1} n_{2}=1.33,$
$ v_{1}=3 \times 10^{8}\, m / s$
$\therefore v_{2}=\frac{v_{1}}{n}=\frac{3 \times 10^{8}}{1.33}$
$=2.55 \times 10^{8} m / s$
Note : The speed of light in water is less than the speed in air. This result obtained by wave theory was found correct by Focault's experiment.