Question

The refractive index of water is $\mathrm{1.33.}$ 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.