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What is a Transformer?

A transformer is made from two coils, one on
each side of a soft iron core. It can increase the voltage
(called a step up transformer, shown below)
or decrease the voltage (called a step down transformer).

How does a Step Up Transformer Work?

Step Up Transformer

Alternating current is passed through the primary coil (the input)
which creates a changing magnetic field in the iron core.
The changing magnetic field then induces alternating current
of the same frequency in the secondary coil (the output).

A step up transformer has more turns of wire on the secondary coil,
which makes a larger induced voltage in the secondary coil.
It is called a step up transformer because the output voltage
is larger than the input voltage. If the secondary coil
has twice as many turns of wire then the output voltage
will be twice the input voltage. See the transformer equation.

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