physics: the first sciencequantum physics 260 12.1 the “old” quantum physics 261 12.2 the new...

Physics: The First Science

RUTGERS UNIV

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RUTGERS UNIV

ERSITY PRESS

Physics: The First Science

Peter Lindenfeld and Suzanne White BrahmiaRutgers, The State University of New Jersey

RUTGERS UNIVERSITY PRESSNew Brunswick, New Jersey, and London

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Library of Congress Cataloging-in-Publication Data

Lindenfeld, Peter.Physics : the first science / Peter Lindenfeld and Suzanne White Brahmia.

p. cm.Includes bibliographical references and index.ISBN 978-0-8135-4937-8 (pbk. : alk. paper)

1. Physics—Textbooks. I. Brahmia, Suzanne White, 1963– II. Title.QC23.2.L55 2011

530—dc222010021009

A British Cataloging-in-Publication record for this book is available from the British Library.

Copyright © 2011 by Peter Lindenfeld and Suzanne White Brahmia

All rights reserved

No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, or byany information storage and retrieval system, without written permission from the publisher. Please contact RutgersUniversity Press, 100 Joyce Kilmer Avenue, Piscataway, NJ 08854–8099. The only exception to this prohibition is“fair use” as defined by U.S. copyright law.

Visit our website: http://rutgerspress.rutgers.edu

Manufactured in the United States of America

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Contents

Preface ix

Additional Notes, Primarily for theInstructor xi

Acknowledgments xv

CHAPTER 1

Atoms to Stars: Scales of Size, Energy,and Force 1

1.1 The microbe and the elephant: thehierarchy of size 2

1.2 Energy and stability 51.3 The four forces 71.4 Atoms and the periodic table

of elements 81.5 Seeing atoms: the scanning tunneling

microscope 111.6 Summary 121.7 Review activities and problems 12

CHAPTER 2

Some Tools of the Trade: Numbers,Quantities, and Units 16

2.1 The language of physics: symbolsand formulas 17

2.2 Once more the four forces, this timequantitatively 26

2.3 Summary 282.4 Review activities and problems 28

CHAPTER 3There Is No Rest: Describing Motion 33

3.1 Getting started: simplification andapproximation: models 34

3.2 Keep your eye on the ball: where isit and where is it going? 35

3.3 The mathematics of change 463.4 Summary 493.5 Review activities and problems 49

CHAPTER 4

Forces and Motion: Newton’sFramework 57

4.1 Newton’s laws of motion 584.2 Adding forces: vectors 624.3 Momentum and its conservation:

action, reaction, and Newton’sthird law 71

4.4 One more motion that iseverywhere: rotation 77


CHAPTER 5Laws and Their Limits: The Organizationof Scientific Knowledge 90

5.1 How do we know? Reality andinterpretation 91

5.2 The Newtonian model and itslimitations 97

5.3 Mechanics and beyond 995.4 Summary 1005.5 Review activities and problems 101

CHAPTER 6Energy and Its Conservation 103

6.1 Work: not always what youthink 104

6.2 Energy of motion: kineticenergy 105

6.3 Energy of position: potentialenergy 106

6.4 Friction and the loss of mechanicalenergy 113

6.5 Internal energy and the law ofconservation of energy 116

6.6 Work and energy revisited 1186.7 Power: not what the power

company sells 1256.8 Summary 1256.9 Review activities and problems 126

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vi / Contents

CHAPTER 7Materials and Models 135

7.1 Ideal systems and models:the ideal gas 136

7.2 Other systems: adding piecesfrom reality 146


CHAPTER 8Electricity: It Is Everywhere 158

8.1 The electric force 1588.2 The electric field 1608.3 Field lines and flux 1658.4 Summary 1718.5 Review activities and problems 172

CHAPTER 9More on Electricity: From Force to Energy,from Field to Potential 176

9.1 Electric potential energy and electricpotential 177

9.2 Energy transformations and electriccircuits 187


CHAPTER 10

Magnetism: Electricity’s TravelingCompanion 198

10.1 Again—force, field, andmotion 199

10.2 The electron: an old friend turnsout to be the elementalmagnet 210

10.3 Generating electricity: motional emfand Faraday’s law 212


CHAPTER 11

Waves: Mechanical andElectromagnetic 223

11.1 What is a wave? 22411.2 What can waves do? Describing

waves and their properties 22611.3 Sound and musical scales 22911.4 Maxwell’s great contribution:

electromagnetic waves 233

11.5 Observing interference of light 23711.6 Reflection and refraction 24111.7 Where Einstein started:

electromagnetism andrelativity 247


CHAPTER 12Quantum Physics 260

12.1 The “old” quantum physics 26112.2 The new synthesis 27012.3 Order in the universe:

the elements 28112.4 Summary 28612.5 Review activities and problems 288

CHAPTER 13The Nucleus: Heart of the Atom 293

13.1 Henri Becquerel, Marie Curie, andthe beginning of nuclearphysics 294

13.2 What is the universe made of?The stable nuclei and their bindingenergy 295

13.3 Radioactivity 29813.4 Biological effects 30313.5 The nuclear force 30513.6 Observing radioactive

radiations 30613.7 Nuclear reactions 30813.8 Particles 31413.9 Summary 315

13.10 Review activities and problems 317

CHAPTER 14Energy in Civilization 322

14.1 The flow of energy 32414.2 Electric energy: what is it and

what does it do for us? 32514.3 DC and AC: transformer and

generator 32514.4 Energy storage 32614.5 Entropy and the second law of

thermodynamics: the limits ofenergy transformation 328

14.6 Our addiction to fossil fuels 33114.7 Other sources of energy 333

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Contents / vii


CHAPTER 15

Atomic Physics Pays Off: Solar Cells,Transistors, and the Silicon Age 339

15.1 The real solid: metals, insulators, andsemiconductors 340

15.2 Tiny changes and vast consequences:impurities in semiconductors 342

15.3 The transistor and the informationrevolution 344


CHAPTER 16There Is No End 349

Bibliography 351

Some Constants, Astronomical Quantities,and Masses 353

Index 355

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To Lore, who saw this book come to life,and was the first to listen to some of its passages.

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Preface

The world is a wonderful place. Our aim is thatworking with this book will help you to be moreaware of it than you were before and to see itmore fully, both the aspects that are visible andthose that are hidden.

Let’s look at the different parts of this book.First there is the text. We hope that you find itclear, interesting, and sometimes surprising. Wewant this to be a book that you read. In betweenthe narrative passages are the examples. Theyturn the words into action. They are essentialparts of the book, and it is very important thatyou read and study them carefully. Each examplehas questions, usually with numbers and quanti-ties. Working through them is not difficult sincethe answers are there too.

You might think that leaves nothing for youto do. That’s where the “Guided Review” comesin. There is one at the end of each chapter. Foreach example in the text there is a Guided Reviewquestion that is closely related to it. The idea isthat as you think about the question at the endof the chapter you will go back to the examplethat goes with it and study it more closely, andalso read and reread the part of the text that goeswith it.

The other questions at the end of the chap-ters are for review, and to let you try out the ideasand the different ways of finding answers. Someof them also take the story further. They aregrouped in sections called “Problems and reason-ing skill building,” “Multiple choice questions,”

and “Synthesis problems and projects.” Forsimplicity all quantities in the examples and otherquestions are assumed to be known to threefigures unless otherwise noted.

A particularly interesting feature consists ofthe simulations that have been developed at theUniversity of Colorado. They give you an evencloser look at the phenomena that are discussedin the text. In most of them you are asked tomake specific measurements, but in addition theyinvite free explorations that take the conceptsfurther.

We should say a little about the math. That’sthe language of physics, and it is important toknow how to use it. We don’t expect you to comeknowing more than you learned in high school.But there may be ways of using math that are newto you, and symbols that are different from thosethat you are used to. We explain them as we goalong. We don’t use calculus in the problems, butwe talk about the ideas of calculus where they arehelpful.

The important part of learning physics is notto memorize facts and formulas. It is, rather, toapproach and analyze unfamiliar situations. Ituses ways of thinking that are accessible to every-one. The study of physics can be frustrating attimes, but also exhilarating and rewarding. Wehope that you will find it to be an adventure thatenriches your view of the world. There may behard work ahead, but we want you to enjoy thetrip that we take together!

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Additional Notes, Primarilyfor the Instructor

We want to change the way physics is taught andthe way it is perceived.

We think there is too much rote learning, toomany formulas, with too little thought, meaning,and overview. There are too many problems thathave no existence outside the elementary physicsclass, too many that are more like games thatthe instructors like to play than searching inves-tigations. We want students to see the subject asa vital part of their world, and as a foundationfor all of the sciences.

Physics: The First Science is an algebra-based text that is both research based and differ-ent from the many textbooks that are currentlyavailable. Our book is less than half as long asthe tomes that have become the norm, and cor-respondingly less expensive. It is designed to beread by the students, we hope with interest, andeven with pleasure. We would like the studentsto think of it as contributing to their learning andoutlook in an important way, and to rememberit long after the course has ended.

The book is supported by the websiterutgerspress.rutgers.edu/physics.html. It allowsus to post comments, additional material, andcorrections, as well as answers and solutions tosome of the questions and problems.

We hope that our book will lead to new pat-terns of teaching. The best courses are transform-ing experiences. We want to help to create such acourse, where the student’s view of the world isenriched by a new awareness and understandingof its phenomena.

Some cherished topics are not there. In par-ticular, we have tried to leave out problems thatmight be called “puzzles.” We believe that theteaching of physics should be clear and direct,and we have made great efforts to keep it so.

The topics follow the usual sequence rea-sonably closely, but we have approached themwith a fresh mind, asking ourselves why eachis included and how it should be presented.Most topics are there because we think of them

as fundamental physics; sometimes because oftheir importance for technology, their societalrelevance, or their historical significance; occa-sionally we add something that we find beautifuland illuminating, or fun and surprising.

MCAT

Many of the students will want to take the Med-ical College Admission Test (MCAT). Accordingto the website of the Association of AmericanMedical Colleges, which administers the test, itnot only asks for mastery of basic concepts insubjects including physics, but also “assessescapacity for problem solving and critical think-ing”, and “evaluates your ability to understand,evaluate and apply information and argumentspresented in prose style.” We have kept therequirements of the test in mind, and believe thatour text provides excellent preparation for it.

Examples and end-of-chaptermaterial

The worked examples are an essential part ofthe reading. They are part of the story line andcan’t be skipped. They are linked to the GuidedReview at the end of the chapter, which con-sists of problems that are alternate versions orminor extensions of the examples. They are fairlysimple to do if you read and work throughthe examples. In that way the Guided Reviewreally forces the student to take the examplesand the associated sections of the book seri-ously. It guides the students’ reading and helpsthem focus on the important concepts. TheGuided Review was a very popular feature withthe students of the class in which the text wastested.

The end-of-chapter material includes ques-tions beyond the Guided Review in sectionscalled “Problems and reasoning skill building,”

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xii / Additional Notes, Primarily for the Instructor

“Multiple choice questions,” and “Synthesisproblems and projects.” These sections provideplenty of practice. Some of the questions alsorequire thought and creativity well beyond thetypical array found in most textbooks and testbanks. Note that all quantities in the examplesand problems are assumed to be known to threesignificant figures unless otherwise noted.

Many simulations are incorporated in thetext, as examples, as parts of the development,and in the end-of-chapter questions. They pro-vide an excellent way to bring the concepts tolife. They were produced by the PhET (PhysicsEducation Technology) project at the Univer-sity of Colorado, initiated by Carl Wieman, aphysicist who decided to devote himself to edu-cation after winning the Nobel Prize for hiswork on atomic physics. Accessing the simu-lations is quite straightforward, but the stu-dents may at first need some guidance. Logonto http://phet.colorado.edu (no www). Theneither “play with sims” or “on line” gets youto the list. Click on “physics,” then on oneof the subdivisions, choose a simulation, andfinally “run now.” We provide explicit questions,but hope that the students (and the instructor!)will go further and try different parts and pos-sibilities. The PhET group occasionally makeschanges to the online simulations so that theinstructions may have to be modified, but thatshould not create major obstacles.

Mathematics

There is no requirement for previous mathemat-ical knowledge beyond high-school algebra. Weintroduce other mathematics when it is appropri-ate. Mathematics is part of the language that weuse, and we foster the development of mathemat-ical reasoning and physics numeracy. We avoidformulaic use and boxed equations. Most oftenthe mathematical development becomes part ofthe narrative.

Calculus is not used in the problems, butits ideas are introduced in terms of slopes andareas, and then used where they are relevant, asin the development of kinematics. Chapter 2 rein-forces mathematical skills that are both vital inour book and often poorly understood, even bystudents who are skilled in “doing problems.”We encourage the students to use mathematics

as a descriptive tool rather than as an algorith-mic puzzle solver. We avoid problems that areprimarily mathematical exercises.

The road map

Atoms, nuclei, and a modern microscopic vieware introduced at the start and referred to fre-quently. This deviates from the practice of leav-ing twentieth-century physics ideas until the endof the course. While we think mechanics is im-portant, we are eager to get to other subjects forwhich there is often too little time. We include anintroduction to quantum properties that is ear-lier and more comprehensive than is usual. Wesometimes discuss phenomena on a microscaleand sometimes on a macroscale, depending onwhich is more appropriate.

The first chapter is an overview that intro-duces atoms and nuclei, scales of size and energy,and the four fundamental forces. It is followedby a review of some of the essential mathemat-ics. The next two chapters are on kinematics andNewton’s laws, and make frequent use of mul-tiple representations, such as motion diagrams,graphs, and energy bar charts.

Chapter 5 discusses the nature of modelsand theories in some detail. It provides an oppor-tunity to think about scientific evidence andthe models and theories based on it. Chapter 6is on energy, not only mechanical but also elec-tric energy and internal energy. Chapter 7 onmaterials and models is organized somewhatnontraditionally. It includes some kinetic theory,fluids, and the first law of thermodynamics, withremarks on quantum theory and other moderndevelopments.

Chapters 8, 9, and 10 are on electricity andmagnetism. Some traditional topics and manytraditional problems are left out, but there issome material that is not usually included. Thesame is true for Chapter 11 on waves, which, inthe spirit of the book, deals with sound, light, andelectomagnetic waves so as to show their com-mon features and their differences. Chapter 12 isintellectually perhaps the most important chap-ter. It begins with the “old” quantum theory,including the Bohr model, primarily to introdu-uce some basic quantities and concepts, whilemaking clear from the outset where it is inad-equate. The chapter proceeds to the modern

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Additional Notes, Primarily for the Instructor / xiii

synthesis of particles and waves, both for pho-tons and particles, and discusses this fundamen-tal feature of modern physics without resort tomystery or paradox in a way that we think ismore straightforward and understandable thanmost others that we have seen. It is followed bythe chapter on nuclear physics, which is quiteextensive.

Chapters 14 and 15 represent major depar-tures from the usual subject matter. The chapterEnergy in Civilization, more than any other,demonstrates the importance of physics in soci-etal issues. It also includes an introduction toentropy and the second law of thermodynamics.We think that it makes these topics more acces-sible than is usually the case. Finally, we felt thatwe could not leave out the concepts and devicesunderlying our electronic age, and end with achapter that describes some of what is behind thegadgetry that every child now grows up with.

Highways and byways

Even with our drastic cuts, there remains morematerial in the book than is manageable in theusual one-year course. There are sections, exam-ples, and problems that an instructor may wishto leave out, and others that can be assigned tobe read without spending much class time. Weare very aware of the need to deal with unfamil-iar concepts in some depth and with sufficienttime. Each instructor will need to construct hisor her own road map. For each part you canchoose the level of intensity that you wish touse. The first is to read so as to become famil-iar with the concepts. The second is to studyand be able to make straight-forward applica-tions. Finally, there is the intense involvementthat leads to deeper understanding and allowsthe use of the material in unfamiliar situations.Here are some suggestions for variations.

We like our first chapter, but wouldn’texpect to spend a lot of time with it. Similarly,Chapter 2 can be dealt with rather quickly withmoderately experienced students. Chapter 5 isshort, and much of it can be a reading assign-ment.

The last section of Chapter 7 consists oftopics that are not generally included, and may

be assigned as extra reading. It’s an advantage toget to the end of Chapter 7 with time to spare,because Chapter 8 on electricity can then be partof the first semester. This allows a fast startto the second semester and additional time forthe more sophisticated sections to come. Chap-ters 8, 9, and 10 are basic, but not everyonewill want to deal with each part in the samedepth. This applies, for instance, to Gauss’s law(in Chapter 8), to the brief part where calcu-lus is used in Chapter 9, and to Section 10.2 onthe microscopic aspects of magnetism. The sec-tions on sound (11.3) and light (11.5, 11.6) offeroptions, and so does the section on relativity inChapter 11.

Even though Chapter 12 is important, therecan be variations in depth and emphasis. Weregard most of the first part and the qualita-tive introduction to the Schrödinger equation asessential, but we realize that the following sec-tions have parts that are more difficult and gofar beyond the usual subject matter of a one-yearintroductory course.

Chapter 13 on nuclear physics is more ex-tensive than usual, but uses only simple algebra.Candidates for bypasses are the semiempiricalbinding energy relation, and Section 13.6 on theobservation of radioactive radiations.

The review of present-day energy use inChapter 14 may be the first part of the book to beovertaken by what happens. Since it comes nearthe end it is in danger of being left out. It wouldbe better to assign it as extra reading. It shouldthen be possible to spend some class time on thesection on the second law of thermodynamics.Finally, the instructor will have to decide howmuch time is left for Chapter 15.

In summary, we believe that we have a thor-oughly modern course that is open, inviting, andaccessible. Some sections are easier and morebasic than usual, and some are more sophisti-cated. Each instructor will have to decide what toinclude and what to emphasize. Earlier versionsof the text were tested during three successivesummers at Rutgers University in a course forpremed and science majors. The instructor wasnot one of the authors, but it contributed to thesuccess of the book that he was sympathetic toits aims and ideas, and that the procedures andexams reflected the spirit of the book.

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Acknowledgments

We would like to thank our colleagues at Rut-gers University for their support and encour-agement, especially Premala Chandra, EugeniaEtkina, Charles Glashausser, Noémie Koller,Paul Leath, and Alan Van Heuvelen. Alan VanHeuvelen pioneered the use of multiple represen-tations, including energy bar charts. Some of theexamples and problems had their origin in thecollaboration of S.W.B with him and EugeniaEtkina.

We would like to acknowledge the role ofGeorge Horton (1926–2009) in making our col-laboration possible. His was a lifetime effort tohelp to create a culture in which caring aboutstudent learning has a very high value.

P. L. would like to acknowledge discussionswith Art Hobson, whose writings influenced thesection on the synthesis of wave and particlephenomena. The section on the sustainabilitytransition was inspired by the work of his friendand mentor Robert W. Kates.

Helpful comments on early versions of partsof the manuscript were made by E. L. Jossem,Arthur Kosovsky, Mario Iona, and ChristianRömelsberger.

Special thanks go to Lonni Sue Johnson forher drawings, including the one on the cover.

We have incorporated activities based onthe PhET interactive Simulations developed bythe Physics Education Technology group at theUniversity of Colorado, licensed under a CreativeCommons Attribution United States License. Wethank them for their openness and cooperation.

The book has profited greatly from the con-tributions of Michael J. Gentile, who was the firstto use it as a text in a course. On the basis of thisexperience he made many thoughtful and help-ful comments and suggestions that have led tonumerous improvements in the present version.

P. L. and S.W.B.August 2010

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physics: the first sciencequantum physics 260 12.1 the “old” quantum physics 261 12.2 the new...

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