Question

The frequency of a light wave in a material is $2\times 10^{14}Hz$ and wavelength is $5000\mathring{A}$. The refractive index of material will be

• A. 1.40
• B. 1.50
• C. 3.00
• D. 1.33

Answer 1

Answer: (C)

Velocity of light waves in material is
$v=v\lambda$ ...(i)
Refractive index of material is
$\mu =\frac{c}{v}$ ...(ii)
where $c$ is speed of light in vacuum or air
or $\mu =\frac{c}{v\lambda }$ ...(iii)
Given, $v=2\times 10^{14}Hz$
$\lambda =5000\mathring{A}=5000\times 10^{-10}m$
$c=3\times 10^{8}m/s$
Hence, from Eq. (iii), we get
$\mu =\frac{3\times 10^8}{2\times 10^{14}\times 5000\times 10^{-10}}=3.00$