A transformer is a device that changes electricity at one voltage into electricity at another voltage. Likely, you have seen a gray or green can that looks like a garbage can bolted to a power pole. Every farmyard has one. That is a transformer. In this activity, you will learn more about transformers.

Transformers are used by power companies because the most efficient way for them to transmit alternating current (AC) power long distances is to use very high voltages. Very large transmission lines can carry up to a half of a million volts! What do you think would happen if a half of a million volts hit your television set? That's right — no more television set and probably no more house because of the explosion and fire that would result!

Voltage is a measure of how much electrical energy a charged particle carries. Current means that you have a steady flow of the charged particles.

Inside a transformer are two coils of wire wrapped around a metal core. The picture below shows a "step-down" transformer. This is the device ordinarily on a power pole in a farmyard. It is called a step-down transformer because the output voltage is smaller than the input voltage. It reduces the voltage to what you can use in your house.

The power comes into the above diagram from the left. It flows through the wire with many turns. This is called the primary coil. This causes a magnetic field that induces (or produces) a current in the wire with few turns, which is called the secondary coil. The AC (alternating current or load) then travels at the correct voltage along the wires to where it is needed.