The Study of Elementary Electricity and Magnetism by Experiment Containing Two Hundred Experiments Performed with Simple, Home-made Apparatus — Key Ideas to Explore

CHAPTER XIV. CONSTRUCTION AND USE OF APPARATUS 89

Exp. 101, To study the effect of the electric current upon the magnetic needle.--Electrical Connections.--Current Detectors.--Exp. 102, To study the construction and use of a simple "key."--Exp. 103, To study the construction and use of a simple "current reverser."--Exp. 104, To study the simple current detector.--Exp. 105, To study the construction and use of the simple galvanoscope.--Discussion; True Readings.--Exp. 106, To study the construction and use of a simple astatic needle.--Astatic Needles.--Exp. 107, To study the construction and use of a simple astatic galvanoscope.--Astatic Galvanoscopes.

CHAPTER XV. GALVANIC CELLS AND BATTERIES 102

Exp. 108, To study the effect of dilute sulphuric acid upon carbon and various metals.--To amalgamate.--Dilute sulphuric acid.--Discussion.--Exp. 109, To study the effect of dilute sulphuric acid upon various combinations of metals.--Discussion.--Exp. 110, To study the construction of a simple Voltaic or Galvanic cell.--The Electric Current.--Source of the Electrification.--The Electric Circuit; Open and Closed Circuits.--Plates or Elements.--Direction of Current.--Poles or Electrodes.--Chemical Action in the Simple Galvanic Cell.--Action in Cell Using Impure Zinc; Action Using Pure Zinc.--Exp. 111, To see what is meant by "local currents" in the cell.--Local Action; Local Currents.--Reasons for Amalgamating Zinc Plates.--Exp. 112, To study the "single-fluid" Galvanic Cell.--The Simple Cell.--Polarization of Cells.--Effects of Polarization.--Remedies for Polarization; Depolarizers.--Exp. 113, To study the "two-fluid" Galvanic Cell.--Setting Up the Two-Fluid Cell.--Care of Two-Fluid Cell.--Copper Sulphate Solution.--Chemical Action in the Two-Fluid Cell.--Various Galvanic Cells; Open and Closed Circuit Cells.--The Leclanché Cell--Dry Cells.--The Bichromate of Potash Cell.--The Daniell Cell.--The Gravity Cell.

CHAPTER XVI. THE ELECTRIC CIRCUIT 115

Exp. 114, To see what is meant by "divided circuits" and "shunts."--Divided Circuits; Shunts.--Exp. 115, To see what is meant by "short circuits."

CHAPTER XVII. ELECTROMOTIVE FORCE 117

Electromotive Force.--Unit of E. M. F.; The Volt.--Exp. 116, To see whether the E. M. F. of a cell depends upon the materials used in its construction.--Discussion.--Electromotive Series.--Exp. 117, To see whether the E. M. F. of a cell depends upon its size.--Discussion.

CHAPTER XVIII. ELECTRICAL RESISTANCE 120

Resistance.--Exp. 118, To study the general effect of "resistance" upon a current.--External Resistance; Internal Resistance; Unit of Resistance; The Ohm.--Resistance Coils; Resistance Boxes.--Simple Resistance Coil.--Exp. 119, To test the power of various substances to conduct galvanic electricity.--Conductors and Nonconductors.--Exp. 120, To find the effect of sulphuric acid upon the conductivity of water.--Internal Resistance.--Exp. 121, To find what effect the length of a wire has upon its electrical resistance.--Discussion.--Exp. 122, To find what effect the size (area of cross-section) of a wire has upon its electrical resistance.--Discussion.--Exp. 123, To compare the resistance of a divided circuit with the resistance of one of its branches. Discussion.--Exp. 124, To study the effect of decreasing the resistance in one branch of a divided circuit.--Current in Divided Circuits.

CHAPTER XIX. MEASUREMENT OF RESISTANCE 130

Exp. 125, To study the construction and use of a simple Wheatstone's Bridge.--The Simple Bridge.--Equipotential Points.--Example.--Exp. 126, To measure the resistance of a wire by means of Wheatstone's Bridge; the "bridge method."--Allowances for Connections.--Exps. 127-137, To measure the resistances of various wires, coils, etc., by the "bridge method."--Table.--Exp. 138, To study the effect of heat upon the resistance of metals.--Effect of Heat upon Resistance.--Exp. 139, To measure the resistance of a wire by the "method of substitution."--Simple Rheostat.--Exp. 140, To measure the E. M. F. of a cell by comparison with the two-fluid cell.--Exp. 141, To measure the internal resistance of a cell by the "method of opposition."

CHAPTER XX. CURRENT STRENGTH 142

Strength of Current.--Unit of Current Strength; The Ampere.--Measurement of Current Strength.--The Tangent Galvanometer.--The Ammeter.--The Voltameter.--Unit of Quantity; The Coulomb.--Electrical Horse-power; The Watt.--Ohm's Law.--Internal Resistance and Current Strength.--Exp. 142, Having a cell with large plates, to find how the strength of the current is affected by changes in the position of the plates, the external resistance being small.--Exp. 143, Same as Exp. 142, but with small plates.--Exp. 144, To find whether the changes in current strength, due to changes in internal resistance, are as great when the external resistance is large, as they are when the external resistance is small.--Discussion, with examples.--Arrangement of Cells and Current Strength.--Cells in Series.--Cells Abreast.--Exp. 145, To find the best way to join two similar cells when the external resistance is small.--Exp. 146, To find the best way to join two similar cells when the external resistance is large.--Best Arrangement of Cells.

CHAPTER XXI. CHEMICAL EFFECTS OF THE ELECTRIC CURRENT 151

Chemical Action and Electricity.--Electrolysis.--Exp. 147, To study the electrolysis of water.--Composition of Water.--Electromotive Force of Polarization.--Exp. 148, To coat iron with copper.--Exp. 149, To study the electrolysis of a solution of copper sulphate.--Electroplating.--Exp. 150, To study the chemistry of electroplating.--Discussion.--Electrotyping.--Voltameters.--Exp. 151, To study the construction and action of a simple "storage" cell.--Secondary or Storage Cells.

CHAPTER XXII. ELECTROMAGNETISM 158

Electromagnetism.--Exp. 152, To study the lines of force about a straight wire carrying a current.--Ampere's Rule.--Lines of Force About Parallel Wires.--Exp. 153, To study the lines of force about a coil of wire like that upon the galvanoscope.--Exp. 154, To study the magnetic field about a small coil of wire.--Coils.--Polarity of Coils.--Exp. 155, To test the attracting and "sucking" power of a magnetized coil or helix.--Exp. 156, To find whether a piece of steel can be permanently magnetized by an electric current.--Exp. 157, To study the effect of a piece of iron placed inside of a magnetized coil of wire.

CHAPTER XXIII. ELECTROMAGNETS 165

Electromagnets.--Cores of Electromagnets.--Exps. 158-163, To study straight electromagnets; Lifting power; Residual magnetism of core; Magnetic tick; Magnetic figures; Magnetic field.--Horseshoe Electromagnets.--Use of Yoke.--Experimental Magnets.--Method of Joining Coils.--Exps. 164-173, To study horseshoe electromagnets; To test the poles; To study the inductive action of one core upon the other; Magnetic figures; Permanent Magnetic Figures; Lifting power; Residual magnetism when magnetic circuit is closed.--Closed Magnetic Circuits.

CHAPTER XXIV. THERMOELECTRICITY 175

Exp. 174, To find whether electricity can be produced by heat.--Home-made Thermopile.--Thermoelectricity.--Peltier Effect.--Thermopiles.

CHAPTER XXV. INDUCED CURRENTS 178

Electromagnetic Induction.--Exp. 175, To find whether a current can be generated with a bar magnet and a hollow coil of wire.--Discussion.--Induced Currents and Work.--Exp. 176, To find whether a current can be generated with a bar magnet and a coil of wire having an iron core.--Exp. 177, To find whether a current can be generated with a horseshoe magnet and a coil of wire having an iron core.--Induced Currents and Lines of Force.--Exp. 178, To find whether a current can be generated with an electromagnet and a hollow coil of wire.--Exp. 179, To find whether a current can be generated with an electromagnet and a coil of wire having an iron core.--Discussion of Exps. 178-179.--Exp. 180, To study the effect of starting or stopping a current near a coil of wire or other closed circuit.--Exp. 181, To study the effect of starting or stopping a current in a coil placed inside of another coil.--Discussion of Exps. 180-181.--Direction of Induced Current.--Laws of Induction.--Primary and Secondary Currents.--Exp. 182, To see what is meant by alternating currents.--Direct and Alternating Currents.--Self-induction; Extra Currents.

CHAPTER XXVI. THE PRODUCTION OF MOTION BY CURRENTS 187

Currents and Motion.--Exp. 183, Motion produced with a hollow coil and a piece of iron.--Exp. 184, Motion with hollow coil and bar magnet.--Exp. 185, Motion with electromagnet and piece of iron.--Exp. 186, Motion with electromagnet and bar magnet.--Exp. 187, Motion with electromagnet and horseshoe magnet.--Exp. 188, Motion with two electromagnets.--Discussion of Exps. 183-188.--Exp. 189, Rotary motion with a hollow coil of wire and a permanent magnet.--Exp. 190, Rotary motion with an electromagnet and a permanent magnet.--Discussion of Exps. 189-190.

CHAPTER XXVII. APPLICATIONS OF ELECTRICITY 192

Things Electricity Can Do.--Exp. 191, To study the action of a simple telegraph sounder.--Discussion.--Telegraph Line; Connections.--Operation of Line.--Exp. 192, To study the action of the "relay" on telegraph lines.--The Relay.--Exp. 193, To study the action of a two-pole telegraph instrument.--Exp. 194, To study the action of a simple "single needle telegraph instrument."--Exp. 195, To study the action of a simple automatic contact breaker, or current interrupter.--Automatic Current Interrupters.--Exp. 196, To study the action of a simple electric bell, or a "buzzer."--Electric Bells and Buzzers.--Exp. 197, To study the action of a simple telegraph "recorder."--Exp. 198, To study the action of a simple "annunciator."--Discussion.--Exp. 199, To study the shocking effects of the "extra current." Induction Coils.--Action of Induction Coils.--Transformers.--The Dynamo.--The Electric Motor.--Exp. 200, To study the action of the telephone.--The Telephone.--The Bell, or Magneto-transmitter.--The Receiver.--The Carbon Transmitter.--Induction Coils in Telephone Work.--Electric Lighting and Heating.--Arc Lamps.--The Incandescent Lamp.

CHAPTER XXVIII. WIRE TABLES 208

A Few Dont's for Young Students.

Don't fail to make at least a part of your own apparatus; there is a great deal of satisfaction and pleasure in home-made apparatus.

Don't experiment in all parts of the house, if working at home. Fit up a small room for your den, and carry the key.

Don't begin an experiment before you really know what you are trying to do. Read the directions carefully, then begin.

Don't rush through an experiment to see what happens at the end of it. See what happens at each step, and notice every little thing that seems unusual.

Don't try to do all parts of an experiment at the same time. Understand one part, then proceed.

Don't fail to ask yourself questions, and form an opinion about the results of an experiment before you read what the author has to say about it.

Don't fail to keep a note-book. Keep all the data and arithmetical work for future reference.

Don't leave the apparatus around after you have finished the day's work.

_=1. Introduction.=_ We should know something about iron and steel at the start, because we are to use them in nearly every experiment. The success with some of the experiments will depend largely upon the quality of the iron and steel used.

When we buy a piece of iron from the blacksmith, we get more than iron for our money. Hidden in this iron are other substances (carbon, phosphorus, silicon, etc.), which are called "impurities" by the chemist. If all the impurities were taken out of the iron, however, we should have nothing but a powder left; this the chemist would call "chemically pure iron," but it would be of no value whatever to the blacksmith or mechanic. The impurities in iron and steel are just what are needed to hold the particles of iron together, and to make them valuable. By regulating the amount of carbon, phosphorus, etc., manufacturers can make different grades and qualities of iron or steel.

When carbon is united with the _pure_ iron, we get what is commonly called iron.

_=2. Kinds of Iron and Steel.=_ _Cast iron_ is the most impure form of iron. Stoves, large kettles, flatirons, etc., are made of cast iron. _Wrought iron_ is the purest form of commercial iron. It usually comes in bars or rods. Blacksmiths hammer these into shapes to use on wagons, machinery, etc. _Steel_ contains more carbon than wrought iron, and less than cast iron.

_Soft steel_ is very much like wrought iron in appearance, and it is used like wrought iron.

_Hard steel_ has more carbon in it than soft steel. Tools, needles, etc., are made of this.

=EXPERIMENT 1. To study steel.=

_Apparatus._ A steel sewing-needle (No. 1).[A]

[Footnote A: _=NOTE. Each piece of apparatus used in the following experiments has a number. See "Apparatus list" at the back of this book for details. The numbers given under "Apparatus," in each experiment, refer to this list.=_]

=3. Directions.= (A) Bend a sewing-needle until it breaks. Is the steel brittle?

(B) If you have a file, test the hardness of the needle.

_=4. Discussion.=_ "Needle steel" is usually of good quality. It will be very useful in many experiments. Do you know how to make the needle softer?

=EXPERIMENT 2. To find whether a piece of hard steel can be made softer.=

_Apparatus._ Fig. 1. A needle; a cork, Ck (No. 2); lighted candle (No. 3). The bottom of the candle should be warmed and stuck to a pasteboard base.

=5. Directions.= (A) Stick the point of the needle into Ck, Fig. 1, then hold the needle in the flame until it is red-hot. (The upper part of the flame is the hottest.)

(B) Allow the needle to cool in the air.

(C) Test the brittleness of the steel by bending it. Test its hardness with a file (Exp. 1).

_=6. Annealing.=_ This process of softening steel by first heating it and then allowing it to cool slowly, is called _annealing_. All pieces of iron and steel are, of course, hard; but you have learned that some pieces are much harder than others.

=EXPERIMENT 3. To find whether a piece of annealed steel can be hardened.=

_Apparatus._ The needle just annealed and bent; cork, etc., of Exp. 2; a glass of cold water.

=7. Directions.= (A) Heat the bent portion of the needle in the candle flame (Exp. 2) until it is red-hot, then immediately plunge the needle into the water.

(B) Test its brittleness and hardness, as in Exp. 2.

_=8. Hardening; Tempering.=_ Good steel is a very valuable material; the same piece may be made hard or soft at will. By sudden cooling, the steel becomes very hard. This process is called _hardening_, but it makes the steel too brittle for many purposes. By _tempering_ is meant the "letting down" of the steel from the very hard state to any desired degree of hardness. This may be done by suddenly cooling the steel when at the right temperature, it not being hot enough to produce extreme hardness. (The approximate temperature of hot steel can be told by the colors which form on a clean surface. These are due to oxides which form as the steel gradually rises in temperature.)

=EXPERIMENT 4. To test the hardening properties of soft iron.=

_Apparatus._ A piece of soft iron wire about 3 in. (7.5 cm.) long (No. 4); the candle, water, etc., of Exp. 3.

=9. Directions.= (A) Test the wire by bending and filing.

(B) Heat the wire in the candle flame as you did the needle (Fig. 1), then cool it suddenly with the water. Study the results.

_=10. Discussion.=_ Soft iron contains much less carbon than steel. The hardening quality which steel has is due to the proper amount of carbon in it. If you have performed the experiments so far, you will be much more able to understand later ones, and you will see why we are obliged to use soft iron for some parts of electrical apparatus, and hard steel for other parts.

_=11. Kinds of Magnets.=_ Among the varieties of magnets which we shall discuss, are the natural, artificial, temporary, permanent, bar, horseshoe, compound, and electro-magnet.

_The Horseshoe Magnet_, H M (Fig. 2), is the most popular form of small magnets. The red paint has nothing to do with the magnetism. The piece, A, is called its _armature_, and is made of soft iron, while the magnet itself should be made of the best steel, properly hardened. The armature should always be in place when the magnet is not in use, and care should be taken to thoroughly clean the ends of the magnet before replacing the armature. The horseshoe magnet is _artificial_, and it is called a _permanent_ magnet, because it retains its strength for a long time, if properly cared for.

=EXPERIMENT 5. To study the horseshoe magnet.=

_Apparatus._ Fig. 2. The horseshoe magnet, H M (No. 16).

=12. Directions.= (A) Remove the armature, A, from the magnet, then move A about upon H M to see (1) if the curved part of H M has any attraction for A, and (2) to see if there is any attraction for A at points between the curve and the extreme ends of H M.

_=13. Poles; Equator.=_ The ends of a magnet are called its _poles_. The end marked with a line, or an N, should be the _north_ pole. The unmarked end is the _south_ pole. N and S are abbreviations for north and south. The central part, at which there _seems_ to be no magnetism, is called the _neutral point_ or _equator_.

=EXPERIMENT 6. To ascertain the nature of substances attracted by a magnet.=

_Apparatus._ The horseshoe magnet, H M (Fig. 2); silver, copper, and nickel coins; iron filings (No. 17), nails, tacks, pins, needles; pieces of brass, lead, copper, tin, etc. (Ordinary tin is really sheet iron covered with tin.) Use the various battery plates for the different metals.

=14. Directions.= (A) Try the effect of H M upon the above substances, and upon any other substances thought of.

_=15. Magnetic Bodies; Diamagnetic Bodies.=_ Substances which are attracted by a magnet are said to be _magnetic_. A piece of soft iron wire is magnetic, although not a magnet. Very strong magnets show that nickel, oxygen, and a few other substances not containing iron, are also magnetic. Some elements are actually repelled by a powerful magnet; these are called _diamagnetic_ bodies. It is thought that all bodies are more or less affected by a magnet.

_=16. Practical Uses of Magnets.=_ Many practical uses are made of magnets, such as the automatic picking out of small pieces of iron from grain before it is ground into flour, and the separation of iron from other metals, etc. The most important uses of magnets are in the compass and in connection with the electric current, as in machines like dynamos and motors. (See experiments with electro-magnets.)

=EXPERIMENT 7. To study the action of magnetism through various substances.=

_Apparatus._ Horseshoe magnet, H M; a sheet of stiff paper; pieces of sheet glass, iron, zinc, copper, lead, thin wood, etc.; sewing-needle. (A tin box may be used for the iron, and battery plates for the other metals.)

=17. Directions.= (A) Place the needle upon the paper and move H M about immediately under it.

(B) In place of the paper, try wood, glass, etc.

(C) Invent an experiment to show that magnetism will act through your hand.

(D) Invent an experiment to show that magnetism will act through water.

_=18. Magnetic Transparency; Magnetic Screens.=_ Substances, like paper, are said to be _transparent_ to magnetism. Iron does not allow magnetism to pass through it as readily as paper and glass; in fact, thick iron may act as a _magnetic screen_.

=EXPERIMENT 8. To find whether a magnet can give magnetism to a piece of steel.=

=19. Note.= You have seen that the horseshoe magnet can lift nails, iron filings, etc.; you have used this lifting power to show that the magnet was really a magnet, and not merely an ordinary piece of iron painted red. Can we give some of its magnetism to another piece of steel? Can we pass the magnetism along from one piece of steel to another?

_Apparatus._ The horseshoe magnet, H M; two sewing-needles that have never been near a magnet; iron filings.

=20. Directions.= (A) Test the needles for magnetism with the iron filings, and be sure that they are not magnetized.

(B) Remove the armature, A, from H M, then touch the point of one of the needles to one pole of H M.

(C) Lay H M aside, and test the point of the needle for magnetism.

(D) If you find that the needle is magnetized, rub its point upon the point of the other needle; then test the point of the second needle for magnetism.

_=21. Discussion; Bar Magnets.=_ A piece of good steel will attract iron after merely touching a magnet. To thoroughly magnetize it, however, a mere touch is not sufficient. There are several ways of making magnets, depending upon the size, shape, and strength desired. For these experiments, the student needs only a good horseshoe magnet, or, better still, the electro-magnets described later; with these any number of small magnets may be made. Straight magnets are called _bar magnets_.

=EXPERIMENT 9. To make small magnets.=

_Apparatus._ Fig. 3. The horseshoe magnet, H M; sewing-needles; iron filings. (See Apparatus Book, Pg. 140, for various kinds of steel suitable for small magnets.)

=22. Directions.= (A) Hold H M (Fig. 3) in the left hand, its poles being uppermost. Grasp the point of the needle with the right hand, and place its point upon the N or marked pole of H M.

(B) Pull the needle along in the direction of its length (see the arrow), continuing the motion until its head is at least an inch from the pole.

(C) Raise the needle at least an inch above H M, lower it to its former position (Fig. 3), and repeat the operation 3 or 4 times. Do not slide the needle back and forth upon the pole, and be careful not to let it accidentally touch the S pole of H M.