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The fact that a changing magnetic flux through a loop
of wire produces an Emf is what has made our civilization
possible. Most people take electricity entirely for
granted --- until the power goes out. Then we get an
initially exciting but quickly tiresome and annoying
glimpse into the way life has been since time zero until
the 20th Century.
Suppose we have a nuclear war and all of civilization
is wiped out, except for a few hardy young souls, like
yourself. You are one of a handful of people left on
Earth with a technical education, and you remember your
physics class at RPI where your professor actually made
a generator from a pile of junk. You can become the
savior of mankind by restoring electric power to the
world. But do you remember how?
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An Emf is produced when you have a magnetic flux changing
in time through a closed conducting path..
Magnetic flux is a magnetic field passing through an
area.
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So, you need one or more of the following:
-- changing magnetic field..... Not so easy.
-- changing area...... Also kind of hard.
-- changing ORIENTATION of the area with the field. Ah
Hah! All you do is rotate the loop of wire in the magnetic
field and you make electricity.
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Get yourself a strong magnet, stronger the
better. Make sure it has a gap large enough to fit a rotating
loop in between the poles.
Make a loop of wire on some support, but give it as many
turns as possible, because each turn produces an Emf,
so 10 turns gives 10xEmf, and 100 turns gives 100xEmf.
Be sure to use insulated wire so it doesn't short out!
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Make slip rings so that you can make electrical
contact with the rotating wire and the outside circuit.
Have a device that can spin the coil as fast as possible
because the faster it spins, the stronger the Emf generated
will be --- ie. The quicker the orientation changes.
Put it all together and enjoy your new job as Exalted
High Wizard for the King's Court.
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| Magnetos |
| The principle of the generator has many other practical
uses. In the early days of the automobile, up until about
1915, cars used devices called "magnetos" to
generate voltage for the spark plugs. |
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| These devices operate on the same principle
as the generator I built --- a rotating coil is in a strong
magnetic field. The reason a magneto gives you a hot spark
is due to a capacitor in the circuit which stores the
energy until the breaker points release it all at once,
every half revolution. The car shown here is a 1914 Franklin
--- and air cooled car made in Syracuse, New York. It
was fast. |
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| Magnetos are still used today as backup ignition on
airplane engines as a reliable, purely mechanical means
of creating spark. Lawn mowers also use magnetos, but
in a different form than the ones pictures here. |
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