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A
transformer uses an input current to make a changing magnetic
field in an iron core. This changing field is used to generate
a voltage in the output coil. Now each turn on the input
coil generates a unit of magnetic field in the iron core
and each turn on the output coil traps a unit of magnetic
field.
For
example if there are 100 loops on the input coil then the
magnetic field in the core will be 100 times as strong as
if there were only one coil. Now what if there are 1000
loops wrapped around this field on the output coil?
Each lot of
100 loops is like the input coil and so gets the same voltage
generated in it as was supplied to the input. But there are
10 lots of 100 loops stacked end to end so the voltages add
up. The output voltage is 10 times the input voltage. Voila
extra voltage!
To
make up for the extra voltage, there is a proportional drop
in current so that the power stays the same.
A
simple reminder is:
power
= voltage x current
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