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Question: 

By what percent is the speed of blue light (450 nm) less than the speed of red light (680 nm), in silicate flint glass (see Fig. 24–14)?

Index of refraction as a function of wavelength for various transparent solids.

Figure 24-14 Index of refraction as a function of wavelength for various transparent solids.

Source: Giancoli, Douglas C., Physics: Principles with Applications, 7th Edition, 2014.

Quick Answer: 

-1.5%

Giancoli 7th Edition, Chapter 24, Problem 18

(1:10)

Chapter 24, Problem 18 is solved.

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Comments

oh, i thought red light has longer wavelengths and is slower than the shorter wavelengths of blue!

Hi spanda2u, you're quite right that red has a longer wavelength, but indeed, as shown in the video, "chromatic dispersion" for most materials usually means the long wavelength colors travel faster. Here's the Wikipedia article (it's rather densely written unfortunately).