A two-port device that transforms a voltage into an analogous quantity can be represented as a simple transformer. A device that transforms a voltage into an analogue of the dual property of voltage (that is, current, whose analogue is velocity) is represented as a gyrator.[27] Since force is analogous to voltage, not current, this may seem like a disadvantage on the face of it. However, many practical transducers, especially at audio frequencies, work by electromagnetic induction and are governed by just such a relationship.[28] For instance, the force on a current-carrying conductor is given by,