The Library of Work and Play: Electricity and Its Everyday Uses

d its centre filled with wire nails. The boys had seen it before and remembered it. With flexible wires I connected the two ends of the wi

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n. When the armature is moved in the opposite direction along the field the needle moves in the opposite direction past zero and on to ten at the left. The moving of the needle in the ammeter shows that we are generating electricity. The swinging to and fro of the needle shows that we are generating an alternating current of electricity. It is a mere matter of detail whether we move the armature or the field, as I will show you by letting the

nds rather indefinitely, but we may say that this particular magnet has an appreciable field extending about one foot in all directions from it. We find upon examination that some magnets have bigger and stronger fields than others, that all have their strongest fields when first magnetized and lose their strength gradually, but never entirely. We find that hardened iron and steel hold magnetism longer than soft iron, but all iron is magnetized somewhat at

his is the meaning of the coils of copper wire around iron cores in the dynamo, in electric bells, in telegraph sounders, in motors, etc., etc. To prevent the electric current from taking the shortest route, through the iron core or th

ribbon. But in the year 1834 he made magnets which lifted thirty-five hundred pounds, to the astonishment of every one. A pair of such electro-magnets as I have here (Fig. 3), each consisting of one pound of No. 24 c

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ric lighting circuit (that in my laboratory is what is called a direct current), and sent a current of electricity around the coils. The two boys and I tugged at the ring in the iron bar to no av

m. Electro-magnets are used for hoisting iron castings weighing many tons. Here is a picture of a

he pull of electro-magnets that moves the electric car. Electro-magnets are now

r electro-magnet with that of the bar

ed the field for magnetic effects. They found that the magnetic field extended six or eight feet, but this piece of research was broken up by a new idea which appe

h by Hele

ri

, judging from the struggle we had with that iron bar a few minutes ago?" The boys looked quite hopeless until I said, "The best thing about the el

unt of electricity which flows, just as well as you may control the flow of water by a faucet or stop-cock. By t

1831, he learned that the reverse was also true, namely, that he could produce electricity from magnetism. This idea coming as the re

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sent around the coil A, that is, the stronger I made the magnetic field, the harder it was to move the coil B. They found that the nearer B was to A the harder it was to move it. They found that the faster they moved B the more electricity was produced. They tried laying B upon its side u

o which you have used much at the summer cottage, but have never seen the inside of. Here are several (see Figs. 5

netos. "Because they have steel magnets for their fields," they re

king several magnets. Have you noticed any armature?" "Yes, i

a dynamo depended upon the amount of energy you expended. Therefore, the strength of the electric current which this machine may produce depends upon two things: (1) the strength of the magnetic field against whic

gas engine, and the others have each a large cog-wheel working into a smaller one. We found

re preparing to report on the magneto as a form of dynamo at the next me

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it first. Connect the binding posts D and E of this magneto (Fig. 5) with my ammeter. Turn the crank very slowly and notice that the needle of

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t as the needle of the ammeter did. Each bell therefore receives one stroke of the hammer for each revolution of the armature. Now try to turn the crank steadily at the rate of one revolution per second. The armature is making six revolutions, or cycles, per second and you now have not only an alternating cur

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of the magneto. Notice that the diaphragm vibrates in time with the alternations of the dynamo. Replace the diaphragm, screw on the cap, hold the receiver to your ear and turn the crank a

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sixty cycles per second, and you notice that you get the same tone that we heard in the dynamo room of the power station and the same tone the telephone receiver gave when I connected it to a coil in our apartment. The tone which is prod

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the light is steady, although it is made by an alternating current passing through the filament in one direction, stopping entirely, and then passing in the oppos