The frequency of a light wave in a material is 2×1014 Hz and wavelength is 5000 Ao. the refractive index of material will be

A
1.40
B
1.50
C
3.00
D
1.33

Solution:

Velocity of light waves in material is

$\begin{array}{l} v = ν λ . . . . (i) \\ Refractive index of material is μ = \frac{c}{v} . . (ii) \\ where c is speed of light in vacuum or air . \\ or μ = \frac{c}{vλ} . . . (iii) \\ Given, v = 2 \times 10^{14} Hz \\ λ = 5000 \overset{o}{A} = 5000 \times 10^{- 10} m, \\ c = 3 \times 10^{8} m / s \\ Hence, from Eq . (iii), we get \\ μ = \frac{3 \times 10^{8}}{2 \times 10^{14} \times 5000 \times 10^{- 10}} = 3 .00 \end{array}$