Transformers are devices that utilize the property of inductance to step-up or step-down voltages. Transformers, however, only work with alternating current, since inductance only occurs when a magnetic field is changing, which is not the case with direct current. However, transformer usage is not limited to voltage modification, it is also capable of matching impedances between different electrical circuits, mating balanced and unbalanced circuits, and isolating dc between circuits, while allowing ac to pass. The basic construction of a transformer consists of two seperate coils of wire wrapped around a core of iron, air, or any ferromagnetic material. While iron and ferromagnetic cores provide much higher coupling (efficiency of induction transfer), there are significant losses through heat generation in the core. Cores can also be shaped differently, such as the rod and E-core designs. The voltage modification is caused by the difference in number of coils on each wire. The wire you have the supply voltage on is referred to as the primary winding. The wire that is receiving the modified voltage is the secondary winding. The level of modification is determined by the ratio of turns between the primary and secondary windings. Current limiting is also provided by the gauge of the wire used in the windings. A thicker gauge wire allows higher amounts of current to go through, while a smaller gauge allows less. Transformers are the primary reason that power transmission and household outlets utilize alternating current. This is because transformers allow for efficient changes in voltage that allow power to be transferred all over the world at high voltages and low costs.


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