Wavelength of light in a medium (23-8)

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Question

Index of refraction of the medium

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Review

Equation 23-8 says that the wavelength is shorter in a medium with a higher index of refraction, where the propagation speed is slower. For example, red light that has a wavelength $\lambda_{\mathrm{vacuum}} = 750$ nm in vacuum has a wavelength in water ( $n$ = 1.33) equal to $\lambda = \lambda_{\mathrm{vacuum}} / n = (750 \mathrm{nm}) / (1.33) = 564$ nm. The frequency of this light is the same in both media: $f = c / \lambda_{\mathrm{vacuum}} = (3.00 \times 10^8 \mathrm{m}/\mathrm{s}) / (750 \times 10^{-9} \mathrm{m}) = 4.00 \times 10^{14}$ Hz in vacuum and $f = v/\lambda = c / (n\lambda) = (3.00 \times 10^8 \mathrm{m}/\mathrm{s}) / ((1.33)(564 \times 10^{-9} \mathrm{m}))= 4.00 \times 10^{14}$ Hz in water.