Question

The frequency of a light wave in a material is $ 2\times {{10}^{14}}Hz $ and wavelength is $ 5000\overset{\text{o}}{\mathop{\text{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\,\,\overset{\text{o}}{\mathop{\text{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 $