Published by Australian Academy of Science
Glossary | Looking down the track at very fast trains

electromagnet. A device that produces a magnetic field using an electric current flowing through a coil of wire, generally wound on a soft iron core. Electromagnets are temporary magnets – when the current is turned off, the magnetism is gone.

polarity. Describes a situation in which there are opposing physical properties at different points in an object or system. When this refers to magnetic poles, the two opposite poles are called ‘North’ and ‘South’; when it refers to electric charges, the two opposite properties are called positive and negative. Unlike poles (and charges) attract; like poles (and charges) repel.

transformer. A device consisting of two coils of wire wound on a soft iron core which is used to change the voltage of an alternating current. Transformers can either increase the voltage (a step-up transformer) or decrease the voltage (a step-down transformer). TV receivers have a step-up transformer that increases the voltage enough to operate the picture tube, and also a step-down transformer to reduce the supply voltage (240 volts) to the 5 volts needed to run transistors.