### Topic Page: transformer

**transformer**

*The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide*

Device in which, by electromagnetic induction, an alternating current (AC) of one voltage is transformed to another voltage, without change of frequency. Transformers are widely used in electrical apparatus of all kinds, and in particular in power transmission where high voltages and low currents are utilized.

A transformer has two coils, a primary for the input and a secondary for the output, wound on a common iron core. The ratio of the primary to the secondary voltages is directly proportional to the number of turns in the primary and secondary coils; the ratio of the currents is inversely proportional.

Step-up transformer This type of transformer has more turnings on the secondary coil than on the primary coil and therefore the voltage induced in the secondary coil is larger than the primary coil voltage. If the number of turns on the primary coil is N_{P} and the number of turns on the secondary coil is N_{S}, and the respective voltages are V_{P} and V_{S}, then N_{S}/N_{P} = V_{S}/V_{P}. For example, if there are 200 turnings on the primary coil and 2,000 turnings on the secondary coil, then the voltage induced in the secondary coil is ten times larger than the primary coil voltage.

Step-down transformer This type of transformer has more turnings on the primary coil than on the secondary coil and therefore the voltage induced in the secondary coil is smaller than the primary coil voltage. The same formula applies as for a step-up transformer, so if there are 2,000 turnings on the primary coil and 200 turnings on the secondary coil, then the voltage induced in the secondary coil is ten times smaller than the primary coil voltage.

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