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ESSENTIALS O F

Applied Physics

ESSENTIALS OF

Applied Physics

A FOUNDATION COURSE FOR

TECHNICAL, INDUSTRIAL, AND

ENGINEERING STUDENTS

By

ROYAL M. FRYE, Ph.D.

Professor of Physics, Boston University

NEW YORK P R E N T I C E - H A L L

,

INC. 1947

COPYRIGHT, 1947, BY

PRENTICE-HALL, INC.

70 FIFTH AVENUE, NEW YORK

ALL RIGHTS RESERVED. NO PART OF THIS BOOK

MAY BE REPRODUCED IN ANY FORM, BY MIMEO￾GRAPH OR ANY OTHER MEANS, WITHOUT PER￾MISSION IN WRITING FROM THE PUBLISHERS.

PRINTED IN THE UNITED STATES Of AMERICA

Preface

Physics is a prerequisite

for courses in the curriculum of junior

colleges, evening engineering schools, technical institutes, and

advanced trade schools, owing to the fundamental position

of the

subject in all branches of engineering work. This book is one of a

series of applied science textbooks designed to meet the needs of

schools where a more concise course is given than is found in the

average college physics textbook, and where numerous topics not

found in a preparatory course in physics are essential.

The orthodox arrangement of, first, mechanics, then sound, heat,

electricity, and light

is followed. Numerous illustrative problems

are completely worked out. A summary of the irreducible minimum

of algebra, geometry, and trigonometry necessary for a clear under￾standing of physics is included in the appendices.

Modern viewpoints on light have been employed, while at the

same time the full advantage of the wave theory of light has been

retained. The electron current is used exclusively, rather than the

conventional positive

current. The practical

electrical units are used

instead of the two c.g.s. electrical systems of units. As preparation

for this, the kilogram-meter-second system, as well as the English

system of units, is used in mechanics. Likewise the kilogram-calorie

is used instead of the gram-calorie.

This work is the outgrowth of the author's experience

in teaching

engineering physics

to many groups of students in evening engi￾neering schools. The material was developed and tested in the

class room over a period of many years. It has proven effective

for students whose needs for practical and applied knowledge of

mechanics, heat, light, and electricity were paramount.

ACKNOWLED9MENTS

The pen sketches at the heads of the chapters and some of those

in the body of the text are the contributions of Louise A. Frye. The

diagrams, in addition to many of the pen sketches, were done by

Ralph E. Wellings. A great many of the illustrative problems,

as

vi PREFACE

well as the index, were prepared by Virginia M. Brigham, who also

typed the manuscript. The author is indebted to Robert E. Hodgdon

for numerous suggestions made during the course of many years

7

association in the teaching of the physics of engineering.

It is impossible

for the author to make adequate acknowledge￾ment to a long line of predecessors

in the field of physics to whom

he is indebted.

ROYAL M. FRYE

Boston

Contents

CHAPTER PACE

PREFACE V

1. INTRODUCTION 1

Why study physics? What is the territory

of physics? Why is

physics the basis of all engineering training? Physical facts.

Physical theories. Units.

2. NEWTON'S LAWS 6

Historical. Newton's first law. Technical terms. Newton's

second law. Newton's third law. Examples of forces which do

and do not illustrate Newton's third law. Newton's law of gravi￾tation. How the law was discovered.

3. FORCE; WORK; ENERGY; POWER 14

Forces. Work. Energy; Conservation of energy. Illustrations of

energy. Potential energy. Kinetic energy. Power. Units of

energy.

4. EFFICIENCY; MECHANICAL ADVANTAGE; COEF￾FICIENT OF FRICTION; SIMPLE MACHINES ... 23

Efficiency. Mechanical advantage. Coefficient of friction.

Simple machines; compound machines. The lever. The pulley.

The inclined plane. The jackscrew. The hydraulic press. Pres￾sure. Pressure energy.

5. FLUIDS 36

Boyle's law. Density and specific gravity. Pascal's principle.

Hydrostatic pressure. Buoyant force; Archimedes' principle.

, Determination of specific gravity.

Bernoulli's principle.

'

6. ELASTICITY 45

Elasticity. Stress. Strain. Modulus of elasticity. Hooke's law.

Bulk modulus. Shear modulus. Bending of beams; twisting of

rods. Ultimate strength.

7, VECTORS 53

Scalars and vectors. The triangle method of adding vectors. The

parallelogram method of adding vectors. Resolution of forces

into components. Properties of certain triangles.

vii

viii CONTENTS

CHAPTER PACE

8. MOMENT OF FORCE; CENTER OF GRAVITY ... 64

Translatory versus rotatory motion. Causes of motion. Moment

of force. Equilibrium. Rules for solving an equilibrium problem.

Center of gravity.

9. ACCELERATION 73

More general conditions. Acceleration. Uniform acceleration.

The two fundamental equations. Graphical representation.

Derived equations. Summary of equations. The acceleration of

gravity. Hints concerning the solution of problems involving

uniform acceleration.

10. PROJECTILES; CENTRIPETAL ACCELERATION . . 83

Velocities and accelerations are vector quantities. Projectiles. A

simple 'projectile problem. A more general projectile problem.

Centripetal acceleration.

11. NEWTON'S SECOND LAW 90

The cause of acceleration. Newton's second law. Formulation

of Newton's second law. Mass. Inertia. Engineering units and

absolute units. Systems of units. Kinetic energy.

12. ANGULAR ACCELERATION; GYROSCOPE 103

Units of angle. Angular speed. Rotatory motion. Angular

velocity. Equations of angular acceleration. Relations between

linear magnitudes on the circumference and the corresponding

angular magnitudes at the center. The gyroscope.

13. DYNAMICS OF ROTATION Ill

Moment of inertia. Derivation of formula of moment of inertia.

Units of moment of inertia. Work and energy of rotation.

Moment of inertia about axis other than center of gravity.

14. CONSERVATION LAWS 119

General survey of the field of mechanics. Impulse and momen￾tum. Conservation of momentum. Conservation of angular

momentum. Illustrations. Variation of mass with speed. "Law

of conservation of mass" no longer held to be true. Conservation

of energy.

15. SIMPLE HARMONIC MOTION; SIMPLE PENDULUM; '

COMPOUND PENDULUM 126

Radial acceleration. Simple harmonic motion. The velocity in

simple harmonic motion. The acceleration in simple harmonic

motion. Technical terms associated with simple harmonic

motion. Force in simple harmonic motion. The simple pendulum.

The physical or compound pendulum. Derivation of fundamental

equation of the compound pendulum. Use of compound pendu￾lum equation to measure moments of inertia. Energy of a body

executing simple harmonic motion.

CONTENTS ix

CHAPTER PAGE

16. PROPERTIES OF WAVES 139

Essential characteristics of a wave transmitting medium. Trans￾verse waves. Longitudinal waves. Technical terms. Reflection.

Refraction. Diffraction. Interference. Polarization. Stationary

waves.

17. SOUND 148

Definitions. No sound in a vacuum. Speed of sound. Depen￾dence of speed of sound on temperature. Pitch, loudness, and

quality. Harmonics. The Doppler effect. Reflection of sound.

Sound represents energy. Time of reverberation. Diffraction

of sound. Interference of sound. Kundt's tube. Organ pipes.

Violin strings.

18. HEAT AND TEMPERATURE: THE TWO LAWS OF

THERMODYNAMICS 161

Heat as a form of energy. Theoretical basis of temperature.

Conversion of energy of motion into heat. Orderly motion tends

to become chaotic, but chaotic motion does not tend to become

orderly. Distinction between heat and temperature. Properties

that depend on temperature. Temperature scales. How to

change from one scale to another. The first two laws of thermo￾dynamics. Generalization of the second law. Entropy; efficiency

of a heat engine.

19. HEAT TRANSFER 170

Three general methods of heat transfer. Conduction; Com￾putation of transfer of heat by conduction. Numerical values of

heat conductivities. More complicated cases. Convection.

Radiation. Computation of transfer of heat by radiation. An

illustration of heat insulation. Perfect reflectors and perfect

absorbers. Thermal equilibrium.

20. EXPANSION 178

Linear expansion

of solids. Coefficients of linear expansion.

Balance wheel on a watch. Volume expansion of solids and

liquids. Volume expansion of gases.

21. CALORIMETRY 184

Measurement of heat. Definition of specific heat. States of

matter. Energy is required to separate molecules. The triple

point diagram. Artificial refrigeration. Heat of vaporization.

Heat of fusion.

22. MAGNETISM 192

Elemetary facts of magnetism. The underlying theory. The

earth as a magnet. Magnetic lines of force. Quantitative aspects

of magnetism. Demagnetization. Additional evidence of the

identification of magnetism with arrangement of elementary

magnets. Magnetism not confined to iron.

x CONTENTS

CHAPTER PAGE

23. STATIC ELECTRICITY 202

How atoms are put together. Conductors and insulators. Static

electricity. Coulomb's electrostatic law. Condensers; capaci￾tance. Voltage. Comparison of magnetic and electrostatic effects.

24. ELECTRICITY IN MOTION; HEATING EFFECT . . 210

Electric currents. Drift speed

of the electrons versus signal speed.

Electromotive force. Ohm's law. Distinction between electro￾motive force and voltage. Resistivity. Heat produced by an

electric current. Hot wire ammeters. Electric light. Electric

power. Thermoelectricity. Some practical aspects of an electric

circuit.

25. VOLTAIC AND ELECTROLYTIC CELLS; SIMPLE

CIRCUITS 221

Voltaic cells. Dry cells. Storage batteries. Chemical effect of the

electric current. Hill diagram. Series and parallel

circuits. Cells

in parallel and in series.

26. MAGNETISM AND THE ELECTRIC CURRENT . . 231

Some of the effects of an electric current are not inside the wire.

Magnetic fields around a current in a wire. The electromagnet.

The electric bell. Comparison of fields produced by currents and

by magnet poles. Flux density. Flux. Dimensions. Effect of a

magnetic field on a current. Comparison of forces exerted by a

magnetic field on poles and currents. Motors and meters. In￾duced electromotive force. Induction coil; transformer. In￾ductance. Lenz's law.

27. ALTERNATING CURRENTS 249

Qualitative description

of an alternating current. Mechanical

analogies. Effect of resistance alone. Effect of inductance alone.

Effect of capacitance alone. The joint effect of resistance, in￾ductance, and capacitance. The rotating vector diagram. The

alternating current equation. Resonance. Power. Alternating

current meters. Parallel circuits.

28. RADIO; RADAR 260

Speed of transmission of a telephone message versus speed of

sound. Electromagnetic waves. Four reasons why radio at one

time seemed impossible. Amplification by means of the radio

tube. Oscillation produced by the radio tube. Modulation pro￾duced by the radio tube. Rectification produced by the radio

tube. Alternating current radio sets. Electronics, Radar.

Radar in war. Radar in peace.

CONTENTS xl

CHAPTER PAGE

29. PHOTOMETRY; REFLECTION AND REFRACTION

OF LIGHT 271

Brief history of the theory of light. The "wave mechanics"

theory of the nature of light. Meaning of "frequency" and "wave

length" in photon theory. Speed of light. Electromagnetic

radiation. Units of length. Photometry. Reflection of light.

Images. Curved mirrors. Refraction of light.

30. LENSES; MISCELLANEOUS PROPERTIES OF LIGHT . 283

Lenses. Formation of a real image by a converging lens. Alge￾braic relationships. Formation of virtual images. Dispersion by

refraction. Diffraction and interference. Dispersion by dif￾fraction. Measurement of "wave lengths." Spectra. Polarization

of light.

APPENDIX 1: Common physical constants and conversion

factors 293

APPENDIX 2: Significant figures and computation rules . . 295

APPENDIX 3: Abbreviated multiplication and division . . 299

APPENDIX 4: Summary of essentials of algebra .... 301

APPENDIX 5: Geometrical propositions

essential to this book . 304

APPENDIX 6: Definition of sine and cosine; sine law, cosine law 305

APPENDIX 7: Table of sines and cosines 307

APPENDIX 8: Three-place logarithm

table 308

APPENDIX 9: The two fundamental theories of physics . .311

APPENDIX 10: List of symbols used in this book .... 313

INDEX 315