Answer:
Explanation:
Due to change in the refractive index of the medium , wavelength changes. If λ be wave length in vacuum , wave-length in refractive index μ
will become λ / μ
Initially no of wavelengths in length L were L / λ
Finally no of wavelengths in length L were L / λ / μ = Lμ / λ
Given
Lμ / λ - L / λ = N
L / λ ( μ -1 ) = N
μ = ( Nλ / L + 1 )