## Conceptual Physics (12th Edition)

Published by Addison-Wesley

# Chapter 26 - Think and Solve: 40

#### Answer

It is shorter. 450 nm. 400 nm.

#### Work Step by Step

If c denotes the speed of light, light in water travels at 0.75c. Speed = (wavelength)(frequency), so $wavelength = \frac{speed}{frequency}$. If the speed is reduced by some factor, and frequency stays the same, then wavelength is reduced by the same factor. Therefore the wavelength of light in water is 75 percent its value in air, or (0.75)(600 nm) = 450 nm. Therefore the wavelength of light in Plexiglas is 67 percent its value in air, or (0.67)(600 nm) = 400 nm.

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