Harper's beginning electricity

Contents

CHAP. PAGE

FOREWORD vii

I. WHAT WE HAVE LEARNED ABOUT ELECTRICITY i

Foreword

ELECTRICITY is as old as the stars. But only recently has it been doing a thousand and one tasks in home iand office, factory and mill, mine and railroad — tasks which are as nothing to its giant strength.

Il The wonder-workings accredited to the fabled genii of j childhood lore are insignificant compared with the marvels which electricity has wrought. A flash, and our messages cross the seas. With the speed of light our voices span the continent. Silently, invisibly, electricity hauls the heaviest trains, accomplishes the hardest tasks. At the pressure of a finger it lights and heats the home. In shop and mill it does more work than all the laborers of the world.

Every one should know something about this mighty energy which blazes into light at the touch of a button, which exerts the strength of giants when a switch is thrown, which faithfully performs the drudgery of home and factory, hesitating at no taskj however menial, however laborious.

This book explains electricity very simply in connection with experiments which any boy can do and devices which any boy can make. This introduction to electricity has been written with the feeling that electricity is a friend and playmate with whom we can easily become intimate. Obviously, the best way to learn about electricity is to do something with it in addition to reading about it. This adds personal interest and entertainment to the acquisition

vii

FOREWORD

of a knowledge which will open up a new world to the beginner and give him a better acquaintance with the electrical wonders of to-day.

Children are taught to keep away from deep water and high cliffs; they are instructed to be careful of machinery of all kinds, of sharp knives and firearms. They should also be taught to respect electricity. Care and prudence are necessary in dealing with all electrical apparatus. 1^' Wherever electricity is carried over long distances, from a water-power station to a cit}" or from village to village, it is under high pressure, and must be left severely alone. These power-wires are always suspended high in the air, but it is dangerous to touch them even accidentally with a fish-pole. If such a line sags low or is accidentally broken, keep away from it.

The wiring about the house should not be tampered with. Houses are wired by competent electricians who take every precaution to guard against any leakage of current — any i' places where the electricity can leave the wires and cause trouble. This wiring is always finally inspected by the insurance authorities, and should be left just as it is installed. The current used for house-lighting is not considered dangerous. There is more danger from serious burns and fires than from "shock," as a result of tampering with the electric-light wires.

Whenever there is new wiring to install, lines to be extended, changes to be made, the work should be trusted to a man experienced in electrical matters.

Leyden jars are used to store up the electricity produced b}^ the static machines. These jars will hold only a little electricity, but it is under enormous pressure. The discharge from a small jar is ver}' unpleasant. The discharge from two or more jars should be carefully avoided. Care

viii

FOREWORD

should also be taken in handling large induction-coils. Never play practical jokes with electricity.

But there are thousands of simple and harmless experiments with electric batteries, motors, static machines, etc., I which cannot fail to interest every one. Electricity is one I of the most absorbing of all our studies. It stimulates the ! imagination, exercises all the faculties, and develops the I mind. Batteries, friction-machines, and toy dynamos are j innocent of any harm. Associating electricity with lightj ning has instilled fear in the hearts of many. Electricity is not to be dreaded, not to be feared. A little education always removes this element of fear.

The author has found by experience that much which is written for younger readers is not sufficiently direct or convenient in its application. Living as the author does in a great electrical center, surrounded by the manifold applications of this tremendous power, he is fully aware of its complexity in use. But he also knows the necessity of introduction — of a beginning, and Beginning Electricity has been planned most carefully to avoid the difficulties often met with in books, and to offer a helping hand to the real beginner.

Don. Cameron Shafer.

Schenectady, New York, June i, 1913.

1^

HARPER^S

'beginning electricity

Chapter I I WHAT WE HAVE LEARNED ABOUT ELECTRICITY

THERE are, generally speaking, three ways of producing an electric current, all very closely related.

Electricity can be produced by rubbing, or friction. This is static, or stationary, electricity.

Electricity can be produced by the action of chemicals. This is known as galvanic electricity, after the Italian scientist Galvani, its discoverer.

Electricity can be secured from magnets. This is termed dynamic electricity. The machine which produces it is called a dynamo.

Electricity can also be produced by heat, a process called thermo-electric generation, but not in quantities large enough to be seriously considered.

We really know a great deal about electricity.

Because electricity is invisible and so very new and strange to most of us is no reason to speak of it in awed whispers. It should not be classified with the mysterious and unknowable. Electricity is a wonderful form of

I energy. We actually know just as much about it, if not more, than we know about steam.

Steam itself is quite as invisible as electricity. That which we see issuing from the tea-kettle spout is not steam, but water-vapor. It is steam being condensed back into water by contact with the cold air. The steam near the hot spout is quite invisible About an inch from the spout it begins to cool. As it cools it condenses into tiny particles of water. It is these minute drops of water that we see and miscall steam. Steam flowing through a hot glass tube cannot be seen any more than we can see electricity flowing I over a copper wire. But we are familiar with steam. We f have known it a long, long time, and intimacy has destroyed the mystery of this form of energy.

Steam is a hot gas capable of great expansion, from which we get mechanical energ3^ This is all we know about 'i steam, although we do know how it behaves under certain f limited conditions.

Some Things that We Know

When we become familiar with electricity, through study and appHcation, it quickly loses its mystery. We are happily surprised to find that we actually know and under- f stand a great deal about this form of energy.

Electricity is a form of energy — and that is all we really f know about it. But we have learned to measure this electric force with the greatest accuracy. We have discovered the laws which govern its behavior under various conditions.

Electricity is much like the force called gravitation. We understand this law of gravitation, that a stone cast from a height will always fall directly toward the center of the earth at a certain increasing speed. The falHng stone is t

ABOUT ELECTRICITY

propelled by a wonderful invisible force called gravitation; but we do not know just what constitutes gravity.

Gravity attracts all things, whether magnetic or not.

Seemingly, it must always travel with a falling body.

! Electricity does not attract all things. Indeed, it repels

I quite as often as it attracts. It not only travels with a

body, but through it. The strange force called cohesion

I exists only in material itself. It cannot travel from one

body to another. Its office is to hold all material together.

Heat must always flow from one body to another. It

i cannot be stored up. Electricity travels freely from one

I body to another, and yet it is not heat.

, Electricity travels with the same speed as light. Light and electricity have no weight, and, therefore, no power of impact It is the weight of the rifle-bullet, plus its speed, which gives it an enormous impact force. As light and electricity weigh practically nothing, they can have no perceptible impact force, even though they travel at enormous speed.

Light, heat, and electricity are all various forms of energy. All are more or less closely related.

Electricity will produce heat; heat will produce electricity. Electricity produces light, and light can produce electricity. Mechanical energy will produce electricity, and electricity, in turn, will produce mechanical energy.

The movement of electricity seems to be like that of water, always from a higher to a lower level. Water is equalized at its lowest level, which is the level of the sea. Raise it above this level and It will always strive to flow back. Electricity seems to have a neutral point. Raise It above this level and it will flow back at every opportunity.

It is true that electricity cannot be seen, and yet It gives the most powerful artificial light in the world. It is noiseless, and yet it causes the mighty peals of thunder and faithfully reproduces the faintest whisper in the telephone. It has no weight, and yet it whirls the largest machinery and hauls the heaviest trains. We cannot see it or weigh it, but we can measure it with the greatest accuracy. We know how fast it travels; we can gage its pressure, its working-energy, the quantity flowing over a wire, or the amount of light, heat, or motive power it will give. The laws which govern its every movement are well known, but y we do not know much about the exact nature of electricity. '

Electricity may be a form of wave-motion, like heat and light and sound. We know that as soon as the molecules in a piece of iron are violently agitated by hammering the ' iron begins to get hot (a molecule is the smallest particle of any material). If the hammering is continued the iron will finally get red-hot. As soon as the iron is hot enough it begins to give out rays of light. As the agitation of the . molecules increases, the brilliancy of the light increases. From red the light turns orange, and from orange to yellow, and finally to a brilliant white light. This heat, and consequent light, can also be produced by the application of electricity to the iron, which would tend to prove that electricity is but a wave-motion.

That electricity has no weight seems to be proven by the fact that a wire weighs exactly the same after being charged with electricity as it did before. The finest scales show no difference in the weight. But a steel bar will be a little longer when magnetized, which shows that electricity has disturbed the molecules of steel in the bar.

Whatever electricity is, for the sake of simplicity let us assume that it is an invisible fluid, without weight, capable of very rapid motion. Just how fast it travels is astonish- u ing. It will flow over an electrical conductor at the terrific

ABOUT ELECTRICITY

speed of 186,165 miles a second, or at nearly the same speed as light. This enormous speed is not appreciated until you stop to think that it will circle the earth nearly eight times within a second. This explains why the telegraph and the telephone are nearl}^ instantaneous, regardless of distance.

Electricity Everywhere

Electricity is present on every side, in everything, in some quantity. The earth is a huge storehouse of electricity. The very air is full of it.

Electricity flows through all substances to a certain degree. Some materials almost wholly oppose, or resist, its passage. Others allow it to move with the greatest freedom. Electricity flows easiest through metals. It will flow through a silver wire as readily as water will flow through a pipe. It will flow through copper almost as well. This latter metal is used almost exclusively where good conductors of electricity are required, because silver is too expensive. Electricity will flow through iron and steel fairly well, but less than one-seventh as well as copper. Electricity does not flow readily through the air or through gases. There are innumerable materials which resist its passage, such as mica, glass, porcelain, rubber, oils, wax, shellac, resin, dry wood, and dry fabrics of all kinds.

We live in a world of electricity, surrounded by it on every side. But we only notice it when it is in motion, or when the quantity present is more or less than the average amount. Electricity is a form of energy and, therefore, cannot be destroyed. It is not aff'ected by heat or cold in ordinary degrees.

Electricity can be easily and quickly changed to other forms of energy. It can be changed to light-energy through the medium of an electric lamp. It can be changed to heat-energy, for heating purposes, by placing resistance or friction in its path. It can be changed to mechanical energy b}^ the application of an electric motor.

And it is in these three forms that we know electricity best.

As a matter of fact, the knowledge of the exact nature of electricity would be of little value to us, beyond adding materially to our scientific discoveries, unless it showed a way to produce this form of energy vastly cheaper than present-day methods. We are interested only in the effects of electrical energy — what it will do — and that is all.

What is electricity t As well ask what is gravity, cohesion, matter. Judging from what has been done in the development of electricity during the past twenty-five years, this question will not long remain unanswered.

p

Chapter II THE BEHAVIOR OF ELECTRICAL ENERGY

THE path over which electricity moves is called a circuit.

This is because electricity always flows in a complete circle, just the same as water flows over a circuitous route. This does not mean that either electricity or water must always travel in a geometrical circle. It is called an electric circuit only because a path must be provided for its return, wherever it is carried, or it will cease to flow. This is equally true of water. The sun raises water from the sea by evaporation. It falls to the mountains in the form of rain. The path must be open for its return to the sea again, or it will cease to flow.

WtR,E

PUSH BUTTON ELECTRIC BELL

Ftff.t

Electricity always flows in a circular path along the various wires (Fig. i). Always it must return to its source. Break or cut the wire at any. point and the flow ceases instantly. This is because a break in the circuit is actually an obstruction in its path. It cannot travel through the air Hke water. Water can be raised from a reservoir with a pump and pushed through a long pipe. As long as this pipe is not obstructed the water will flow back into the reservoir again. Close the pipe at any point and the flow will cease instantly (Fig. 2).

PUMP

Fig. 2

RESERVOIR

Electrical circuits vary in form and extent, but this principle of a continuous path ever remains the same. No matter where electricity is carried over a wire about the house or factory, another wire must be provided for its return to its source or it cannot flow.

Electricity is indestructible. It cannot be used up or destroyed. It is a mistake to think that electricity is consumed and burned up in the electric-hght bulb like kerosene in an oil-lamp. Electricity is not burned and consumed in an electric range like coal in a kitchen stove. The electricity which returns to its original source after its work is done is no diff'erent than it was when it left. It is the working-energy of electricity which is consumed, just as it j is the energy of falling water which is utilized to turn a water-wheel, and not the water itself. Just as much water escapes from the tailrace of a water-power plant as enters the head-gates. Just as much electricity flows back to a battery or dynamo as started over the circuit.

It requires a certain amount of "sun-energy" to raise a quantity of water to a certain height. This energy is thus

ELECTRICAL ENERGY

imparted to the water, and it will produce an equal amount of energy in racing back to the sea. This energy is usually wasted in passing over such rocks and stones as obstruct its path. Water without pressure or elevation has no energy and will do no work. We get electrical power by raising the pressure of electricity with mechanical power, or otherwise, and this pressure will perform a certain amount of work as the current flows back to its source. Electricity without pressure will do no work.

Conductors and Non-conductors

Water will not flow through some materials. It will flow through others with the greatest ease, whereas nearly every substance resists the flow of electricity to a greater or less degree. This quality is well named resistance. The resistance of some materials is greater than that of others. When electricity flows easily through a substance, like copper, the material is said to be a good conductor. This means that it will conduct, or carry, electricity with very little resistance.

Materials which oppose the flow of electricity are called non-conductors. This means that they do not conduct. A conductor covered with a non-conducting substance is said to be insulated. The word insulate is derived from the Latin insula, an island. The word insulated means literally that the body has been isolated, cut oflF from the mainland, removed from electrical communication with all others.

All metals are good conductors. The most common non-conductors are porcelain, glass, mica, stoneware, slate, marble, rubber, oils, parafl&n, shellac, dry paper, silk, cloth, etc.

It requires considerable force to lift water from a reservoir and push it through a long pipe. This is because the pull of gravity and the friction of the inside of the pipe must be overcome. This force is called pressure in hydraulics.

It also requires force to produce motion in electricity. The energy required to push electricity along a wire is called voltage, instead of pressure, although it means about the same thing.

The unit of hydraulic pressure is expressed in pounds to the square inch of surface affected.

The unit of electrical energy is called the volt, in honor of Volta, one of the pioneer discoverers of electricity.

In overcoming the resistance in a wire circuit, the electric current will lose some of its energy, and will, therefore, have less voltage, or pressure, the farther it travels. This difference in voltage in an electrical circuit corresponds to the loss [

A

B

^h h

Fig. 3 i.

QENE

RATOR of pressure in a water pipe, which diminishes rapidl}^ as the pipe is extended from the pump (Fig. 3). To overcome some of the resistance of the wire between A and B the electricity will lose some of its energy. Therefore it will show less pressure at B than at A.

Voltage, or pressure, is sometimes called potential. This word is taken from the Latin potentia, meaning power.

When a wire is carrying a current of electricit}^ it is said to be charged. Electricians also speak of wires as being alive\ and dead. Wires are alive only when carr3ang a current.

ELECTRICAL ENERGY

When a strong current of electricity is sent through the human body it makes the muscles tingle and causes them to contract violently. This sudden contraction of the muscular tissues has led to the adoption of the word shock. When we read that any one has received a shock of electricity it means that they have in some manner interposed a part of their body into an electrical circuit, allowing a portion of the current to travel through the muscles. Only shocks from very high voltage, or potential, are dangerous. The body offers so much natural resistance to the flow of electricity that low voltages, such as are commonly employed for house-lighting, etc., are not considered dangerous.

We may not know exactly what electricity is, but we do know that it is a form of energy. Right here it may be ^ell to explain this natural phenomena we speak of as energy.

Forms of Energy

A person is said to be energetic, to have lots of energy, when he accomplishes a great deal of work. The word " energy " really means a capacity for doing work. When a man walks, when a wheel turns, when a stone is lifted, energy must be expended. And energy, like money, must first be acquired before it can be expended. It is a common belief that energy, once expended, is gone forever. This is far from being true. Energy is never annihilated, never passes out of existence. Energy is quick to change its form, however. It disappears only to reappear in some other shape.

It is easy to show that energy can be made to change its form a great many times. Imagine a steam-pump busy filling a large tank with water. First the energy of the sunshine is stored up in the coal which is being fed to the boilers. This energy of the coal, released by the fire, is

II quickly changed to heat-energy and then to steam-energy. The steam-energy is, in turn, converted to mechanical energy through the medium of the steam-engine. This mechanical energy, acting on the pump, raises the water to the reservoir. After all these changes we now have the original energy of the coal, minus some loss, represented by a quantity of water elevated to a certain height above sea-level.

As long as the water remains in the reservoir it will do no work. The instant the water is released the energy immediately reappears, and may be made to turn a water-wheel. We can belt the water-wheel to an electric dynamo and change the mechanical energy into electrical energy. If we wish we can change this electrical energy back into heat or light energy. By placing a motor in circuit with the dynamo we can change it back to mechanical energy.

It is even possible for us to belt the electric motor to a pump and raise some of the water back to the reservoir. On the face of it this looks as though the great problem of perpetual motion had been solved — but it has not. There are a great many losses every time the form of energy is changed. The energy itself is not lost — it is wasted. It is changed into heat in overcoming friction, and otherwise leaks away. Only a small percentage of the original coalenergy is left in the form of electrical energy. The energy which is lost during these transformations is dissipated, and becomes non-available to man.

The amount of energv, or power, to be obtained from a current of electricity depends upon the quantit}' and its pressure. It is comparable to water in this respect. In considering the power to be obtained from a stream of water we must know the size of the stream and its head, or the height of its fall, which determine the pressure. The energy of a stream of water is always in exact proportion to its fall.

ELECTRICAL ENERGY

A rather large stream, with a fall of but a few feet, will produce a hundred horse-power of energy. A vastly smaller stream, with a hundred-foot fall, will produce an equal amount of working-energy.

In determining the energy of electricity we must always consider the size of the current and its force. Powercompanies fix their charges on the amount of current and the pressure. They cannot fix it upon the quantity consumed, as they do gas and kerosene, because no electricity is consumed. It returns to the power-house, after its work is done, Hke water to the sea.

Chapter III STATIC OR FRICTIONAL ELECTRICITY

THE word static is derived from the Greek statikos, "causing to stand." It is used to express that peculiar characteristic of electricity which causes it to collect to some extent on nearly all materials. It is brought to our notice, usualh^, when it leaps from a charged body with a brilliant spark and a crackling noise.

Static electricity seems to be ever37^where. We are quite surrounded b}^ it on all sides. It is in the earth, the air, in our clothes, on the books, the rug, and the walls. It collects on everything. It sticks the papers together on the desk. It attracts feathers and bits of lint to metal and glass. It leaps from our fingers when we touch "metal objects. Now and then a crackling noise will be heard when the coat is being taken off. A woolen shirt or sweater drawn quickly over the head will produce crackling sparks. By scuffling the dry feet over the carpet a considerable spark can be secured from the fingers.

Bear in mind that static electricity is not the kind that is used to light the electric lamps in the house. Very little work has ever been found for static electricity. It is a worthless vagabond delighting in mad pranks. In the form of lightning it dashes down from the sk}^ scaring honest folk nearly to death, often doing considerable damage. It frequently visits the press-room in large printing- establish-

H

LIGHTNING-DISCHARGE

LIGHTNING STRIKING BUILDING

STATIC ELECTRICITY

ments and sticks the sheets of paper together until the presses have to be stopped. It gathers on the yarns and threads in textile mills, knotting and tangling them, and is always into mischief.

Familiar Forms of Static Electricity

It is easy enough to prove the presence of static electricity. Rub a bit of amber, glass, hard rubber, or sealing-wax with a silk handkerchief or a piece of woolen cloth, and it will attract bits of paper and small particles of metal. When we stroke the cat's back this static electricity collects very rapidly. It snaps and crackles and flashes as it discharges between our fingers and the animal's fur. This display of static electricity is nothing more or less than a miniature thunder-shower — without the rain.

Perhaps the most noticeable manifestation of static electricity is Hghtning. The flash of Hghtning is but a static spark, such as we get from the cat's back, magnified thousands of times.

Lightning is caused by static electricity which has accumulated in the black thunder-clouds. These clouds are carrying an enormous load of static electricity, under heavy pressure, as well as a burden of moisture. When either load becomes too heavy it is dumped off on the earth.

In plainer words, when the particles of moisture condense into large rain-drops and become too heavy to float in the air, we have a shower of water. When the static electricity becomes too condensed to remain longer in the air it discharges to the earth, and we have a shower of electricity.

Air will not conduct electricity to any noticeable degree. In order to cause a static spark between two objects it is necessar}^ to raise the voltage, or pressure, of the current until it is sufficient to "break down" this air resistance so it can jump across. It requires a pressure of nearly 20,000 volts to jump across the first inch of air gap, 40,000 volts for a two-inch gap, 60,000 for a three-inch gap, and so on. If this be true, a discharge of lightning from a cloud to the earth, over a distance of half a mile, must represent an enormous pressure running well up into the millions of volts. A body charged with static electricity evidences some of the peculiarities of a magnet. It is surrounded by a "field of magnetic force." It attracts and repels.

The presence of considerable heat as well as light in any static spark can be easily proven by the ease with which a small spark will light the illuminating-gas or explode a pinch of gunpowder. It requires heat to light the gas or to fire the powder. Light alone will not do this. Even the strongest sunshine cannot light the gas.

The snap following the static spark is probably the vacuum caused by the passage of the current being closed by the normal air pressure, which is fifteen pounds to the square inch.

Static electricity cannot collect on any material unless that material is a non-conductor. A good conductor cannot "collect" a charge of electricity, because the electricity readily escapes over its surface as fast as it is produced and flows back to the earth to maintain the universal balance. You can carry water in a pail, but 3'ou cannot carry it in a sieve. Conductors allow the free passage of electricity, just as the sieve allows the free passage of water. Non-conductors do not allow the passage of electricity, just as the pail holds the water.

A bit of glass, rubbed with silk, evidences static electricity when brought near a bit of paper. When this electricity

STATIC ELECTRICITY

accumulates on the glass it is said to be charged. When the electricity disappears by contact with the finger or any other object the rod is said to be discharged.

If a good conductor of static electricity is insulated it will retain its charge quite as well as any non-conductor. If the sieve is inclosed in a pail it can be said to hold water.

Static electricity spreads rapidly and evenly over the surface of a good conductor. On non-conductors static electricity cannot spread. It must remain in one place until it is carried off, piecemeal as it were, by the molecules of the air.

It will be readily noticed that when static electricity collects on any material it extends an invisible influence out into the atmosphere for a considerable distance. This influence affects anything brought within reach of its lines of force. These invisible lines of force have great penetrating powers. Magnets will attract particles of metals through glass and other non-conducting substances. The *'rays" from a bit of hard rubber, electrically excited by friction, readily penetrate paper, cardboard, and even glass, to attract or repel bits of paper and lint.