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Physics, Techniques and Procedures

Transformer

an electrical device which changes an alternating current of a given voltage and amperage into another alternating current of a different voltage and amperage. A transformer consists of two wire coils wrapped around a closed core (Fig. 1). One of the windings, which is referred to as the primary, is connected to a source of electrical energy. The alternating current in the primary induces a changing magnetic field in the core, which in turn induces an alternating voltage in the secondary windings. Two laws govern the behaviour of a transformer. First, the ratio of the induced voltage to the primary voltage is given by the ratio of the number of turns in the secondary to the number of turns in the primary. Second, except for resistive losses, the input energy equals the output energy. Neglecting resistive losses, the output power, which can be expressed as the product of current and voltage, is the same as the input power. Thus, if the number of turns is greater, the voltage in the secondary will be greater than the voltage in the primary, but the current in the secondary will be proportionately reduced. A step-down transformer decreases voltage and increases amperage. A step-up transformer increases voltage and decreases amperage (Fig. 1).

DLP/HJS-04

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Fig.1

A step-up transformer is shown.
Transformer, Fig.1