Making a transformer

A transformer is a device that converts one AC voltage to another. A
detailed description of how they work is given elsewhere in wikipedia under
transformer. The purpose of this page is to give details of how a
transformer can be made very simply at home or in a classroom in order to
teach the basic principles. Demonstrations similar to this are usually
performed in schools by pupils aged around 13 years old.

You will Need

   * Some pieces of soft iron preferable in a U shape but a cylinder will
     do.
   * Plastic coated wire
   * Some 6V mes bulbs [torch/flashlight bulbs] in a suitable bulb holder
   * Connecting wire with 4mm plugs
   * Crocodile clips
   * A 4V AC Power supply that is fitted with a 5A trip switch

Method

Strip the insulation off the end of a long piece of copper wire and wrap it
30 times around a cylinder of soft iron, to make a solenoid. [If you can use
a U-shaped piece of soft iron then so much the better]. Connect the ends of
the wire into the power supply using crocodile clips or other suitable
connectors. This is called a primary coil. Connect a 6V bulb in parallel
with the solenoid.

Now take another long piece of wire. Strip the ends, and either: wrap it
around the same soft iron core 60 times or [even better] if you have
U-shaped soft iron cores; use a separate core to put the 60 turns on. This
is called the secondary coil

You should now have two pieces of bare ends from the second piece of wire.
Connect them to a 6V bulb so that you have a loop that is independent of the
power supply.

Turn on the power supply and [if applicable] join the two u-shaped soft iron
cores together. Be careful, the primary coil will now be a powerful
electromagnet.

Compare the brightness of the two bulbs. The secondary will be much
brighter.

Repeat with 15 turns on the secondary coil. This time the secondary will be
much dimmer.

This is a quick and dirty demo suitable to teach the basics of transformers.
Other experiments using professionally wound coils and oscilloscopes are
more suitable for more advanced or older students.

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