Physical laboratory manual for use in schools and colleges

Front matter

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the publisher to a library and finally to you.

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to prevent abuse by commercial parties, including placing technical restrictions on automated querying.

Preface

It is generally conceded by science teachers that physics should " be taught by a combination, of laboratory work, text-book, and thorough didactic instruction, carried on conjointly." The attempt to combine practical work and the exposition of principles in the same book has not proved a success in the past; and in view 4 of the difficulties to be overcome, it is very doubtful if it can be satisfactorily accomplished. Before a student is fitted for experimental investigation he must have a clearly defined idea of what it is that he is to do, and how he is to do it ; what he is to expect, what errors are to be guarded against, and how he is to use the results obtained. This requires that he should come to the laboratory well grounded in the first principles of physics as presented in some elementary treatise on the subject, and well read, especially on the subject that he is to investigate, both as to mode of conducting the work, and manner of observing. It is not necessary, however, that the student should traverse the entire subject of physics before entering upon laboratory practice; but he should be kept in his class-work well ahead of the subject forming the basis of his laboratory experiments. To do otherwise is to expect him to rediscover the laws of physics, notwithstanding his lack of skill in manipulation, his ignorance of methods of experimenting, and his inability to make proper observations from not knowing what to look for, when to look, and where to look.

IV PREFACE.

The educational value of practical physics does not lie in the so-called discovery of laws, nor in the experimental demonstration of principles. Indeed, it is very doubtful if the small number of laws the student would be likely to discover would adequately compensate for the large outlay of time that would be necessary, owing to his defective powers of observation, and lack of skill in manipulation. But, rather, its value is to be found in the training it gives in attention to details, in the cultivation of accuracy in observing the smallest changes, in the formation of systematic methods of working, in developing the ability to reason back to a general law from a particular set of observations, and in cultivating habits of precise expression of ideas and principles on the pages of the note-book.

Hence it would seem that the work of the laboratory should be largely quantitative in character, if all these advantages are to be gained by its introduction. Accordingly, the author has attempted to provide such a set of problems judiciously distributed over the several divisions of physics, hoping thereby to touch the subject at most of its chief points, and at the same time keep within the mental grasp of students of secondary schools who are expected to pursue this subject.

Recognizing that comparatively few schools have adopted laboratory methods on account of the difficulty of obtaining apparatus of proper design at reasonable expense, special pains have been taken in selecting problems that could be solved by the aid of simple and inexpensive apparatus. Many of the instruments are not beyond the skill of the average mechanic, and not a few are within the constructive ability of many a bright boy.

In the report of t the Committee of Ten appointed by the National Educational Association in 1892 occurs the following : " To give good instruction in the sciences requires of the

PREFACE. V

teacher more work than to give good instruction in mathematics or the languages, and the sooner this fact is recognized by those who have the management of schools the better for all concerned. The science teacher must regularly spend much time in collecting materials, preparing experiments, and keeping collections in order ; and this indispensable labor should be allowed for in programmes and salaries."

In view of the fact that school officials very rarely make any such allowances as referred to in this report, the science teacher in our public schools is the most overworked person on the staff, and finds it impossible to give the students in the laboratory such instruction and assistance as they must have, in order that the work may yield that training and discipline it is so well calculated to give. Accordingly, the instructions in manipulation of apparatus are made unusually full, and an attempt has been made to anticipate all the important difficulties that are likely to arise. It is hoped that these have been in a large measure accomplished by the liberal introduction of cuts, suggestions, and numerical examples taken from students' note-books. Special attention has been given to the important subject of tabulating and working out results, and deriving from them proper conclusions. The numerical examples will indicate to the beginner how high a degree of accuracy may be expected from the quality of apparatus described, when carefully and intelligently manipulated.

Several valuable appendices conclude the volume, giving aid in the construction and repairing of apparatus, and furnishing a sufficiently complete list of the more important Physical Constants, accompanied by explanations when necessary.

Special acknowledgments are due to The Franklin Educational Co. of Boston, Gage & Son of Boston, Queen & Co. of Philadelphia, Kitchie & Sons of Brookline, Mass., and Goodnow & Wightman of Boston, for the use of a number of illustrations.

VI PREFACE.

The thanks of the author are due to a number of friends who have helped in the revision of the proof-sheets. Of these he would mention Dr. J. Montgomery of the Ann Arbor High School; F. A. Osborne, assistant in the physical laboratory; Geo. L. Chandler, High School, Newton, Mass. ; Preston Smith, High School, Brockton, Mass. ; and J. C. Packard, High School, Brookline, Mass. Although they have contributed in no small degree to the accuracy* of the book, yet they are in no wise responsible for its defects.

H. N. Chute.

Ann Arbor High School Laboratory, August, 1894.

TO THE TEACHER.

I. THE PHYSICAL LABORATORY.

The Room. — Where a separate room can be provided for experimental work in physics, it should be large and well ventilated, and should have a southern exposure. It should either be provided with tight cases for storing apparatus, or there should open off from it a room provided with suitable cases. There should be some provision made for darkening the windows, such as folding-blinds, or frames covered with opaque cloth.

In case that a separate room cannot be provided for a laboratory, then use the recitation-room by placing tables in the back part, rather than omit from the school curriculum this important kind of training. It is now conceded by all wide-awake teachers that a student should be brought in actual contact with the phenomena to be studied by him, if he would know Nature and her laws, and receive from their study mental strength. It was Maxwell who said that a few experiments performed by the student will give him a more intelligent interest in the subject, and will give him a more lively faith in the exactness and uniformity of Nature, and in the inaccuracy and uncertainty of our observations, than any reading of books, or even witnessing of elaborate experiments performed by professed men of science.

The Tables. — A few heavy flat-topped tables, about thirtytwo inches high, four feet wide, and seven feet long, should be

vii viii TO THE TEACHER.

provided. These tables should have no iron in their structure ; and to make it possible to clamp apparatus on them, the top should project about four inches beyond the frame on each side.

Tools. — In one corner of the room, or preferably in an adjacent room, there should be a carpenter's work-bench, provided with vice, anvil, saw, plane, brace, drills, hammer, chisel, soldering-iron, etc. Such tools will be found useful, and in fact necessary, in constructing simple apparatus, and in making repairs.

"Water and Gas. — One or more sinks should be provided, with tables near them, on which to conduct such experiments as may require a continuous supply of water. If there is no water system in the building, a galvanized iron tank might be placed at one end of the sink, and kept filled by a force-pump.

Each table should be supplied with coal-gas by pendants from the ceiling, or brackets on the side-wall, the gas being brought to the table, when needed, by means of rubber tubing. This plan will make it possible to move the tables about the room, changing the arrangement to suit the exigencies of the work. It also frees the tables of obstructions, and introduces no iron pipes beneath them to interfere with magnetic needles.

Reference Books. — It is recommended that a bookcase be provided and well filled with reference books, to which the students may have free access. Such books as the following are recommended : —

" Ganot's Physics," by Atkinson ; " Deschanel's Natural Philosophy," by Everett ; Daniell's " Physics ; " Carhart and Chute's "Elements of Physics;" Cooke's "Chemical Physics ; " Lodge's " Mechanics ; " Thompson's " Electricity and

TO THE TEACHER. ix

Magnetism ; " Poyser^s " Magnetism and Electricity ; " "Heat," by Madan ; "Heat," by Tyndall; "Lectures on the Electromagnet," by Thompson; Fleming's " Short Lectures to Electrical Artisans;" "Elementary Practical Physics," by Stewart and Gee ; " Practical Physics," by Glazebrook and Shaw ; " Physical Manipulations," by Pickering ; " Experimental Physics," by Weinhold ; " The Art of Projecting," by Dolbear; "Practical Mechanics," by Perry; "Physical Measurements," by Whiting; "Lessons in Physical Measurement," by Earl ; " Practical Physics," by Barrett and Brown; "Heat," by Glazebrook; "Light," by Glazebrook; " Sound," by Mayer ; " Sound," by Tyndall ; " Practical Electricity," by Ayrton; "Handbook of Electrical Testing," by Kempe ; " Primary Batteries," by Carhart ; " Mechanics, Sound, and Light," by Carhart ; " Optical Projection," by Wright ; " Lessons and Exercises on Heat," by Hall ; " Experimental Science," by Hopkins; "The Nature of Light," by Lommel; "Light," by Wright; "Popular History of Science," by Koutledge; "Physical Constants," by Everett; Lupton's " Numerical Tables ; " " Electrical Kules and Tables," by Munro and Jamieson ; " Arithmetic of Magnetism and Electricity," by Morrow and Keid.

The walls of the room would be more attractive if they were decorated with the pictures of distinguished scientific men. Bare walls are not very inspiring; good work is not wholly independent of the student's surroundings. Charts of spectra neatly framed would be both useful and ornamental.

It is not to be expected, however", that every luxury, or even every convenience, can be provided at the outset. Let the essentials be secured, and then add from time to time such fixtures as will enable the student to do his work with greater accuracy and at less inconvenience.

TO THE TEACHER.

H. APPARATUS.

How Obtained. — It is a mistake to suppose that elaborate and highly finished apparatus is necessary for successfully prosecuting experimental work. Utility, durability, and efficiency should be considered before display. One should not expect to be able to provide all the required appliances for this manual at the outset. First secure the more important pieces, and then add others as opportunity offers. Much valuable work can be done with a few wisely chosen pieces. A limited amount of apparatus construction by students might be permitted. Nearly every class has its handy boy, whose mechanical gifts can be turned to good account by having him construct some of the simpler apparatus described in connection with the problems. The school janitor is generally a man of some mechanical skill, and can construct frames, supports, and many useful things that will be permanent additions to the collection. Then, if you would succeed, you must turn your own mechanical gifts to account, and spend many an hour at the carpenter's bench or the experimental table, when the other teachers of the school are probably enjoying a rest from labor. The local mechanics of the city or town can build much of the apparatus you may need, and school boards will rarely be found unwilling to spend a few dollars in this way, though they would probably refuse to appropriate a like sum to be spent in some distant city.

The following well-known dealers in and manufacturers of school apparatus can supply any instrument described in these pages : The Franklin Educational Co. of Boston, Mass. ; E. S. Ritchie & Sons of Brookline, Mass. ; Queen & Co. of Philadelphia, Pa. ; and the Eberbach Drug and Chemical Co. of Ann Arbor, Mich. The author, having had dealings with all of these firms, can heartily commend them to the patronage of his fellow science teachers.

TO THE TEACHER. xi

Importing Apparatus Europe is the great storehouse

of physical apparatus ; and, under the law, school officials can import school supplies free of duty. In this way a saving of 30 to 50 per cent can often be effected. This is especially true in the matter of balances, weights, barometers, lenses, mirrors, etc. This importing can be done through any of the above mentioned houses.

Cost of an Equipment. — Many schools are deterred from introducing laboratory methods by false notions regarding the cost. Investigation will show that the first outlay need not be large. Experiments requiring expensive pieces may at first be omitted without seriously affecting either the continuity or the efficiency of the work. Nearly every school already possesses such instruments as air-pump, electrical machine, and their numerous accessories. A few dollars spent for scales, calipers, graduates, balances, lenses, and raw material such* as glass tubing and insulated copper wire, with a room arranged with tables, would enable many a school to fall into line and impart genuine worth to their teaching of physics.

m. LABORATORY MANAGEMENT

Methods. — There are in use two methods of conducting laboratory work, the separate system and the collective system. Under the former the students work on different problems, the apparatus going around in rotation. It is difficult, under this plan, to have the student's work conform to a strictly logical order; but, on the other hand, it requires little or no duplication of apparatus. The collective system is the ideal one. Under it all are engaged on the same kind of work at the same time. It has this advantage over the separate system : a teacher can instruct all at once on any point demanding more than ordinary care, and can give more attention to the

Xll TO THE TEACHEB.

few who may be less apt in their work. A combination of the two is probably the best plan for most schools, in that it avoids the duplication of expensive pieces of apparatus, and permits it in the case of the less costly.

Sections. — Probably the greatest difficulty experienced in experimental physics is to accommodate the large number of students who desire to take up the .subject. The author's plan has been to divide his class into sections of about twenty each, placing two at each table on the same problem. Where classes are so large, it is generally impossible to provide for more than three hours per week ; but if these are well spent, the majority, if not all, of the problems in this manual can be satisfactorily studied in a year.

Assigrnment of Work. — The problems that each student is expected to solve on his appointed day in the laboratory should be assigned to him a few days in advance. An effective and convenient way is to have each section and table numbered ; and then, by a notice posted in a suitable place a week in advance, each student can ascertain what problems he is expected to prepare upon. The author has practised this plan for several years, and has found it in every way satisfactory.

Abridgrment of Work. — Teachers should feel perfectly free to omit any problem or set of problems that they choose. Although all problems are not equally important, yet circumstances will often determine which are to be omitted. To lessen the expense of introducing laboratory practice, it is recommended to duplicate only the cheaper pieces, and to omit the following problems : 25, 28, 29, 33, 39, 42, 43, 52, 61, 63, 90, 92, 94, 95, 105, 107, 122, 123, 124, 131, 132, 133. Of these, it would be wise to add 25, 29, 39, 63, 90, 123, and 132

TO THE TEACHER. Xlll

to the laboratory list as soon as facilities can be supplied. This principle, however, should govern the work : a few problems thoroughly studied will benefit the student more than many superficially gone over.

The School Programme. — In arranging the school programme, some provision should be made for laboratory practice. Physics should never be placed earlier in the school curriculum than the third year. It would be better still to find a place for it in the fourth. The students then come to that study with some mathematical training, which is absolutely necessary to master modern physics. The daily programme should be so planned that the students in physics will have one-half of a day each week free for their experimental work. To divide up their time in the laboratory into short periods is to waste the larger part of it ; for if the time is not sufficiently long to complete an investigation begun, it frequently happens that the part done is lost by having to stop before the whole is completed.

The didactic instruction should run along parallel with the experimental, but a little in advance. At least three recitations per week should be devoted to this work, some suitable text-book being used for the purpose. The objection that is sometimes heard that a student must buy two books is a very shallow one, and may properly be considered as a relic of the Dark Ages. Who ever thinks of objecting to buying three or four books to enable his boy or girl to study a dead language ? Dictionaries and grammars are known to be absolutely necessary. So it should be in studying a science. The student should have what is necessary to insure thorough work, and no intelligent person ought to object to purchasing two small books for a year's study in a subject of such great practical and educational value as modern physics.

TO THE STUDENT.

If you would succeed in the study of the problems presented in this manual, observe carefully the following : —

1. Be orderly and neat in manipulation. Keep all apparatus clean, never setting away any apparatus without wiping it with a chamois or soft cloth.

2. Economize time by remembering that frequently two operations can be carried on simultaneously ; never > however, if either one needs close and constant attention during any considerable period of time.

3. Prepare thoroughly beforehand for every experiment, so that every condition may be faithfully observed, and no failure result from a neglect of some requisite. Do not substitute for what is the best you can provide, that which will barely do.

4. Ascertain the reason for every step taken in working through an experiment, noting which are essential conditions permitting no variations, and which are non-essential only in so far as they conduce to greater accuracy, and hence may be modified as circumstances may suggest or make necessary.

5. Be exact and methodical. Let nothing pass unnoticed, although you may not see its significance at the moment. Use your own eyes.

6. Keep your note-book by you, and record in it carefully, neatly, and at the time, the results of your observations, and also make sketches of the apparatus used. Tabulate facts whenever possible.

7. Never enter on a new experiment till you have disposed of the last one in a manner satisfactory to yourself and to the teacher in charge of the work.

Chapter I. Page

Introduction 1

CHAPTER II. Simple Measurements

I. Measurements of Length, Area, and Volume ... 8

II. Measurement of Mass 26

HI. Cohesion 36

CHAPTER IH.

Mechanics op Solids, —

I. Composition of Forces 43

II. Curvilinear Motion 46

III. Accelerated Motion 49

IV. The Pendulum 51

V. The Simple Machines 54

CHAPTER IV. Mechanics of Fluids

I. Pressure in Fluids 60

II. Pressure on the Bottom of a Vessel 63

III. Law of Boyle 65

IV. The Siphon 67

V. The Principle of Archimedes 68

VI. Determination of Density .,,.,,.... 70 xv xvi CONTENTS.

CHAPTER VIII. Light

I. Images Through Small Apertures 154

II. Photometry 156

III. Reflection of Light .159

IV. Mirrors 162

V. Refraction of Light .171

CONTENTS. XVll

APPENDICES.

' PAGE

A. — Directions for Making Apparatus 185

B. — Laboratory Operations 193

C. — Physical Constants, —

I. Capillarity 199

II. Densities of Various Substances 199

III. Electrical Resistance 202

IV. Approximate Electromotive Force of Primary Bat-

teries 202

V. Electrical Resistance, etc., of Copper Wire .... 203

VI. Acceleration due to Gravity 204

VII. Relative Thermal Conductivity 205

VIII. Boiling-points of Substances $05

IX. Coefficients of Expansion

X. Latent Heats of Liquefaction and Vaporization . . 206

XI. Melting-points 207

XII. Specific Heat 207

XIII. Indices of Refraction 208

XIV. Mensuration Rules 208

XV. Lengths, of Seconds Pendulum 209

XVI. Velocity of Sound at 0° C 209

XVII. Tenacity 209

XVIII. Trigonometrical Functions 210

XIX. Some Useful Numbers 212

XX. Reduction Rules 213

D. — Price List of Apparatus and Material 214

PHYSICAL LABORATORY MANUAL.

Introduction

1. The Note-book. — Each student should have a note-book in which to record the work done by him in the laboratory. It should be known as the Laboratory Note-book, and should be devoted exclusively to the work of the laboratory. It should be made of good paper, which, for convenience in drawing figures, tabulating facts, and representing related quantities by curves (6)', should be ruled in small squares. All records of results obtained in any experiment should be made on the right-hand page ; the left-hand page facing these results being reserved for diagrams and computations. All notes should be carefully written with due regard to clearness and completeness of statement ; all measurements of magnitude should be tabulated. The laboratory hour should not be devoted to writing discussions of experiments, nor to making computations, only so far as the results of these computations may be needed for immediate use ; on the other hand, it should be given up wholly to observational work, collecting data to be used and studied at home. No records should be made and taken from the laboratory on loose leaves of paper, since these are liable to get mislaid. The note-book should always be made the book of original entry, thereby excluding errors due to copying and to defective memory.

All readings of magnitudes should be recorded in the terms given by the scale of the instrument. When reduced to other forms, the reductions should be recorded separately and distinctly marked as such.

Avoid crowding the notes ; give the record plenty of room, and aim to make it intelligible to others. Make the record full. It is better that it should contain an occasional irrelevant fact, than that important ones necessary to a full analysis of the problem should be omitted.

2. Preparation. — As thorough a study as possible without actually manipulating the apparatus should be accorded to each problem before undertaking its solution in the laboratory. In this way the time spent in the laboratory can be made much more productive of results ; the work done will be intelligently done, more accurately done, and more quickly done, since the student will have only the manipulation to learn, the principles involved being already in mind.

3. The "Weekly Report. — On the completion of any experiment, the student should submit his note-book to the instructor in charge of the laboratory for examination and approval, before taking up another experiment. This preliminary report consists of the following parts : (1) A statement of the object of the problem, followed by the date on which the work was done. (2) The apparatus used, each piece being

INTRODUCTION. 3

designated in such a manner that subsequent identification will be possible. (3) The manner of conducting the experiment, wherever it differed from the plan outlined in the text-book. (4) The records made in the laboratory as the experiment proceeded, the several determinations of the same thing being recorded in tabular form, and all related quantities appearing in parallel columns properly designated.

This preliminary report should be supplemented by the addition of the following, and handed to the instructor at the end of the week : (5) An account of the theory of the experiment, presenting any mathematical considerations bearing on the conclusions \o be established. For example, if the problem be that of finding the density of a substance, it should be pointed out what is meant by density, and how it is related to the magnitudes it is proposed to measure in the course of the experiment. (6) References to books consulted in preparing the report, giving title and page. (7) Additions to the table of results of the computations found on the opposite page. (8) The discussion of the results obtained. The student should study the observations he has recorded with a view of finding out their interpretation. Whenever possible, he should compare them with those given by theory, and compute the amount of the error. He should carefully examine the method pursued in conducting the experiment, and ascertain all the principal sources of error.

Every part of the report should be written with great care, both from a scientific and from a rhetorical standpoint, since the report will be an accurate measure of the mental acumen of the student.

4. The Term Report. — The student should correct all errors pointed out by the instructor, rewriting the report if necessary, to put every point in proper form. This revised report should be submitted at the end of the term for more careful examination.

5.. Errors in Observing. — Errors are unavoidable. Absolute accuracy is impossible. The value determined for any quantity is just as liable to be greater than the true value as it is to be less. The calculated mean of a large number of observations is probably nearer the true value than any single determination. By taking a large number of observations, the student acquires facility in handling tKe apparatus, becomes more familiar with the principles applied, and thereby is likely to increase the accuracy of his work.

On account of the facility with which errors are made, it is advisable to vary the conditions as much as possible, to the end that new combinations may arise and the repetitions of old errors be avoided. " Check methods " should be used whenever possible; even if not calculated to give close results, they will assist in detecting errors. The aim should be to secure the highest degree of accuracy attainable with the quality of apparatus and the amount of time at one's disposal.

All observations should be recorded, even if known to be far from right, unless they were made simply for practice. If any observations are discarded in the calculations, reasons for doing so should be entered in the notes.

6. Graphic Representation of Data. — This method is employed to show to the eye the relation between two quanti-

INTRODUCTION. 5

ties which are so connected that any change in the value of one is attended by a change in the other ; as, for instance, the height to which water rises in a capillary tube is greater the smaller the diameter of the tube. It consists in representing by a line the data obtained by the observer in the course of his investigations, the shape of the line indicating the form of the law connecting the interdependent facts.

To construct the line,. procure a piece of cross-section paper of suitable size, or use a page of the note-book if the ruling is accurate, and of the kind specified in Art. 1. The cross-section paper is preferable, since the small squares are of known value, being usually either 1 mm. or .1 inch on a side. Select some suitable scale to be used in representing the things to be compared, the chief condition being that the scale unit should be such as will bring all the work on the sheet or page.

In some instances the sum of the sides of several of the squares may constitute the linear unit ; in others, the side of a square may represent several units. It is not necessary that the same unit be chosen for both magnitudes involved. After selecting suitable units, measure toward the right on the horizontal line passing through the corner of some one of the squares, called the Origin, a sufficient number of spaces and parts of a space to represent the numerical value of the first of the dependent quantities ; and then, in the perpendicular through the point just located, measure off a distance to represent the numerical value of the second quantity, marking the point thus located. In like manner locate points, using