Patterns of light : chasing the spectrum from Aristotle to LEDs

204 Pages·2008·12.49 MB·English

by  Steven Beeson

Patterns of Light
A nearly complete overview of this book can be found in Archimedes’ Burning-
Mirrors from Witelo’s Optics written c. 1270. In the woodcut, we see light trav-
eling in straight lines, reflection, mirrors, images, bent legs in water, rainbows,
blue sky, and clouds. The rest of the electromagnetic spectrum, invisible to the
eye, yields no fewer clues about both microscopic and distant worlds. The opti-
cal properties of elephants we leave to the valiant.
Steven Beeson and James W. Mayer
Patterns of Light
Chasing the Spectrum from Aristotle to LEDs
StevenBeeson JamesW.Mayer
WaterfrontTechnologies CenterforSolidStateScience
Washington,DC20010 ArizonStateUniveristy
USA Tempe,AZ85287-1704
[email protected] USA
[email protected]
ISBN978-0-387-75106-1 e-ISBN978-0-387-75107-8
LibraryofCongressControlNumber:2007936185
(cid:2)c 2008 SpringerScience+BusinessMedia,LLC
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“Come forth into the light of things. Let nature be your teacher.”

-- Wordsworth, 1788

“The electron is not as simple as it looks.”

--W. Lawrence Bragg
Steve Beeson:

To my parents, Donald and Luana, who always see the light inside

Jim Mayer:

To my wife, Elizabeth
Preface
Light is all around us. Vision is our dominant sense, and we are richly rewarded
with a palette of colors from red to violet. Our eyes do not detect the low-
energy, long-wavelength infrared (IR) radiation, but we know it exists from dis-
cussions of war applications and televised images of guided weapons targets.
Our eyes do not detect the higher-energy (above visible light energies) and
shorter-than-visible-wavelength ultraviolet radiation, and yet we know it is there
from the sunburn we receive in Arizona. We also know that window glass can
block ultraviolet rays so we don’t get a burn while driving with the windows
rolled up.
We know about radio waves from the little boxes that talk to us and x-rays
from the dentist office. These waves and rays belong to the same family of light,
often called photons (from the Greek photos, light), that describes the spectra of
electromagnetic radiation over 10 orders of magnitude from very low-energy ra-
dio waves to very high-energy x-rays and gamma rays.
This book starts with the visible — the straight path of light — because what
we can see is a good starting point. It continues with reflection as we look at
ourselves in mirrors and storefront windows. It includes a chapter on refraction,
its discovery and description, and a chapter on lenses, which are familiar to the
myopic (eyeglasses) and the football fan (binoculars). Color is introduced with
the query, Why is the sky blue? After answering that and other similar ques-
tions, the book goes beyond the visible to the infrared and ultraviolet. It ends
with analysis of Mars using x-ray emission.
This is a descriptive book rather than a technical book. It is designed for the
general reader with no background in science but who has an interest in the light
around us. There is an Internet site associated with the text called Images of Na-
ture (http://ion.eas.asu.edu). It provides optical and electron microscopy images
that can be downloaded by the reader and student for free. The site also provides
additional information on x-ray emission techniques and comparisons between
optical and electron microscopy. For the educator or curious reader, exercises,
solutions, and exams are available by writing to the publisher.
The book originated in a general studies course at Arizona State University in
the curriculum of Physical Science and in that of Society, Values and Technol-
ogy. The course started with the support of Terry Woodin of the National Sci-
ence Foundation for K–12 teachers. It expanded to the general undergraduate
X Preface
population at Arizona State University and its enrollment is at 150 students each
semester (enrollment started with 10 students in Elementary Education). Verne
Hess of NSF supported Images.
At Arizona State University we want to thank Sue Wyckoff for her support
through the Arizona Collaborative for Excellence in Teacher Preparation. We
thank Elizabeth Mayer, who participates in the ASU course; Frank Mayer for
handling the lab sessions; Rod Heyd, our web-master; and Misty Wing for
manuscript preparation. Michael Weiland and Marc van Horne provided IT
course support.
Thanks to Danny Adams and Rudolph Nchodu of the University of the West-
ern Cape and Frank Mayer for the three years of Patterns workshops given to
high school teachers in South Africa. Images of Nature arose out of their
interest.
Steve Beeson would like to acknowledge the US Department of Labor for the
time and computing resources in finishing this work. Additional thanks go to
Alison, Lisa, and Lilly for advice; to Tyler for use of the ’vette; and to Laura and
Karen for inspiration.
The line drawings were done by Jane Jorgensen and Ali Avcisoy. They were
redrawn by Don Thompson of Graphixx.
T. von Forster read the original version and made extensive suggestions,
which lead to the final manuscript.
Linda Young edited the manuscript. She has a sharp eye and made many cor-
rections and improvements to the present manuscript.

James W. Mayer Steve Beeson
Tempe Washington, DC
May 2007 May 2007
Contents

1 The Path of Light................................................................................................1
1.1 The Straight and Narrow..............................................................................1
1.2 The Fastest Thing Around............................................................................3
1.3 Standing in the Shadows..............................................................................5
1.4 The Reversible Path of Light.......................................................................7
1.5 The World through a Hole...........................................................................8
1.6 A Room with a View.................................................................................10
2 The Reflection of Light.....................................................................................13
2.1 Reflections on the Past...............................................................................13
2.2 All Things Equal........................................................................................15
2.3 From the Looking Glass.............................................................................16
2.4 The Curved Mirror.....................................................................................19
2.5 Shaving and a Spoon..................................................................................20
2.6 The Rough Edges.......................................................................................22
3 Daguerreotypes: Light Captured....................................................................25
3.1 A Race to Capture Light............................................................................25
3.2 Tripping the Light Fantastic.......................................................................26
3.3 It’s all in the Reflection..............................................................................29
4 The Refraction of Light....................................................................................33
4.1 From Galaxy to Fish..................................................................................33
4.2 Altering the Speed of Light........................................................................33
4.3 The Light Brigade......................................................................................36
4.4 The Properties of Waves............................................................................38
4.5 On the Beach..............................................................................................40
4.6 The Law of Refraction...............................................................................42
4.7 The Refractive Index..................................................................................43
4.8 Total Internal Reflection............................................................................45
4.9 Diffraction: Newton’s Mistake..................................................................46