Chapter 12 – Wave Optics

12.0 Introduction

Photograph of the reflective side of a C D. Regions of the disc reflect a rainbow of colors.
The colours reflected by this compact disc vary with angle and are not caused by pigments. Colours such as these are direct evidence of the wave character of light. (credit: Infopro, Wikimedia Commons)
Examine a compact disc under white light, noting the colours observed and locations of the colors. Determine if the spectra are formed by diffraction from circular lines centred at the middle of the disc and, if so, what is their spacing. If not, determine the type of spacing. Also with the CD, explore the spectra of a few light sources, such as a candle flame, incandescent bulb, halogen light, and fluorescent light. Knowing the spacing of the rows of pits in the compact disc, estimate the maximum spacing that will allow the given number of megabytes of information to be stored.

If you have ever looked at the reds, blues, and greens in a sunlit soap bubble and wondered how straw-coloured soapy water could produce them, you have hit upon one of the many phenomena that can only be explained by the wave character of light, as shown below.  The same is true for the colours seen in an oil slick or in the light reflected from a compact disc. These and other interesting phenomena, such as the dispersion of white light into a rainbow of colours when passed through a narrow slit, cannot be explained fully by geometric optics. In these cases, light interacts with small objects and exhibits its wave characteristics. The branch of optics that considers the behaviour of light when it exhibits wave characteristics (particularly when it interacts with small objects) is called wave optics (sometimes called physical optics). It is the topic of this chapter.

Soap bubbles reflecting mostly purple and blue light with some regions of orange.
Figure 2. These soap bubbles exhibit brilliant colours when exposed to sunlight. How are the colours produced if they are not pigments in the soap? (credit: Scott Robinson, Flickr)

This textbook is based on Open Stax College Physics.   You can download the original book for free at < https://openstax.org/details/college-physics > .   This is Chapter 27 in that book.

 

 

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Douglas College Physics 1207 Copyright © August 22, 2016 by OpenStax is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.