A monochromatic light of frequency 5 × 10¹⁴ Hz travelling through air, is incident on a medium of refractive index ' 2 '. Wavelength of the refracted light will be :

Solution

Physics sir · 3 steps

Frequency never changes on refraction, so the wavelength shrinks by exactly the refractive index.

1. Frequency stays fixed. The frequency is set by the source, so it is the same in air and in the medium. Only the speed changes, and the wavelength changes with it.
2. Wavelength in air. λₐᵢᵣ = c/f = (3 × 10⁸)/(5 × 10¹⁴) = 6 × 10⁻⁷ m = 600 nm.

   λ_(medium) = v/f = (c/μ)/f = λₐᵢᵣ/μ

3. So. λ_(medium) = (600 nm)/2 = 300 nm, which is option (b).

The idea to keep. When light enters a new medium, frequency stays the same while speed and wavelength both drop by the factor μ. Find the air wavelength first, then divide by μ.

Answer from the NTA final answer key. Solution by PrepWiser.