How Do Transformers Affect Electricity?

Transformers are used in towns and cities to reduce the voltage of electricity flowing in transmission lines to lower, more useful voltages. They are also used to reduce the voltage of domestic mains electricity--the standard, 110-volt supply in U.S. homes--so it can be used by laptop computers, MP3 players and battery chargers.

How Transformers Work

• An alternating, or fluctuating, electrical current flowing through a wire creates a magnetic field around the wire. Similarly, when a fluctuating magnetic field surrounds a wire, it creates, or induces, a current in the wire. So, by placing one coil of wire next to another, it is possible to create a current in the second coil by passing current through the first.

Decreasing Voltage

• If the second coil contains fewer turns than the first, the voltage of the electricity flowing through it will be less than the original. This is the basis of "step-down" transformers, which are used in a range of domestic electrical devices, from hair dryers to game consoles.

Increasing Voltage

• Conversely, if the second coil has more turns than the first, the voltage will be higher than the original. This is the basis of "step-up" transformers, which are widely used in long-distance power transmission and to operate 220-volt products from a 110-volt supply.