A monochromatic electromagnetic wave of frequency $1.2 \times 1 0^{15} Hz$ propagates in glass whose refractive index is $n = 1.4$ . Calculate the wavelength of the wave in the glass.

easy 1 mark Class 12 · Physics · Electromagnetic Waves

Answer

1.78 \times 1 0^{- 7} m

The correct answer is $1.78 \times 1 0^{- 7} m$ — Insert the values: $λ = \frac{2.14 \times 1 0 ^{8}}{1.2 \times 1 0 ^{15}} = 1.78 \times 1 0^{- 7} m$ .

Step-by-step solution

Use the speed of light in vacuum $c = 3.00 \times 1 0^{8} m s^{- 1}$ .
The speed of the wave in glass is $v = \frac{c}{n} = \frac{3.00 \times 1 0 ^{8}}{1.4} = 2.14 \times 1 0^{8} m s^{- 1}$ .
Wavelength is related to speed and frequency by $l amb d a = \frac{v}{f}$ .
Insert the values: $λ = \frac{2.14 \times 1 0 ^{8}}{1.2 \times 1 0 ^{15}} = 1.78 \times 1 0^{- 7} m$ .

Common mistake: Dividing frequency by refractive index instead of speed

Concept tested: Wavelength in a medium from refractive index

Published 11 September 2026 · Last updated 16 September 2026 · How this solution was prepared and checked

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A monochromatic electromagnetic wave of frequency 1.2×1015Hz propagates in glass whose refractive index is n=1.4. Calculate the wavelength of the wave in the glass.

Step-by-step solution

A monochromatic electromagnetic wave of frequency $1.2 \times 1 0^{15} Hz$ propagates in glass whose refractive index is $n = 1.4$ . Calculate the wavelength of the wave in the glass.