Download Ch-37-Summary - Stout Middle School

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Chapter 37 Summary – Electromagnetic Induction
Electromagnetic Induction is inducing current in a wire by a changing magnetic
field near a wire. This means that magnets can produce electricity and electricity can
produce magnets. It doesn’t matter which is moving, the coil of wire or the magnet, but
a changing magnetic field near a coil of wire will induce voltage and a current carrying
wire will have a magnetic field around it. How much voltage is induced depends on 2
things: how many loops of wire, and how fast they move. The catch is it takes more
force to move near more loops, and it takes more force to move faster. Generators and
motors both rely on electromagnetic induction and are made of the same parts. A
generator inputs mechanical energy (a force) to move a coil of wire near magnets,
induce voltage, and output electrical energy. A motor inputs electrical energy, generates
magnetic fields around coils of wire which interact with other magnets and output
mechanical energy (forces). The current changes direction every time the magnet
changes direction or the coil turns 180 degrees. Our biggest problem with generating
electricity is how to get that input force to move the coil. Our most common way is
with steam pressure, but wind and water can create forces too. Transformers increase or
decrease voltage through electromagnetic induction. Power stays the same and current
is inversely proportional. A transformer is 2 coils of wire wrapped around an iron core.
The input side is called the primary coil, the output side is called the secondary coil.
The voltage is transformed based on the ratio of primary coil loops to secondary coil
loops. If a transformer had 20 loops on the primary and 40 loops on the secondary and
the primary voltage was 120 volts, the secondary voltage would be 240 volts. If a
transformer had 30,000 volts on the primary and 5,000 volts on the secondary and it had
100 loops on the secondary, the primary coil would have 600 loops.