Light of wavelength 2400 x 10-10 m in air will become light of wavelength in glass (µ = 1.5) equal to

Light of wavelength 2400 x 10-10 m in air will become light of wavelength in glass (μ = 1.5)
equal to
A. 1600 x 10-10 m B. 7200 x 10-10 m C. 1080 x 10-10 m D. none of these

The speed of light in vacuum is equal to the product of the index of refraction and the speed of light through that substance. c = n1v1 = n2v2 , since the frequency is constant then the product of wavelength through a medium and its index of refraction in that medium is equal to its wavelength in new medium and its new index of refraction, n1x1 = n2x2. The answer is A, 2400/1.5 = 1600.

Grigori S. | Certified Physics and Math Teacher G.S.Certified Physics and Math Teacher G.S.

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When light enters a denser medium its speed (v) decreases μ times (see Huygens's principle).Thus, its wavelength equals

λ = vT, where T is the period inversely proportional to the frequency.

But v = c/μ, where c is the speed of light in vacuum. Thus, to calculate new wavelength simply divide 2400 x10^{-10
}by 1.5 and you will get 1600 x10 ^{-10} m.