Photon Color and Light Frequency

Classical Mechanics Level 2

Glass has an index of refraction of about n = 1.5 n = 1.5 . Suppose a photon traveling in glass has a wavelength of 267 nm 267 \text{ nm} in the glass. What is the color of the light represented by this photon?

Yellow Green Purple Red

Matt DeCross by Matt DeCross , 27, USA

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2 solutions

Josie Barszcz
Feb 5, 2020

multiply 1.5 by 267 receiving a wave length of purple

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Matt DeCross
May 10, 2016

Relevant wiki: Amplitude, Frequency, Wave Number, Phase Shift

The effective speed of light in glass is c n = 2 c 3 \frac{c}{n} = \frac{2c}{3} .

To adjust the wavelength to the effective wavelength in vacuum thus requires multiplying by 3/2, obtaining:

λ vacuum = 3 2 ( 267 ) nm = 400.5 nm . \lambda_{\text{vacuum}} = \frac32 (267) \text{ nm} = 400.5 \text{ nm}.

This light is purple, as quoted by 400 nm 400 \text{ nm} = purple in the relevant wiki.

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