A transformer is a device that transfers electrical current from one circuit to another. It does this via electrical induction. Transformers are very efficient. An ideal transformer works very efficiently and can transfer over 99% of its energy from the input's circuits to the output's circuits. Transformers are used for many electrical devices and come in a wide variety of sizes. Inside a stage microphone is a small transformer approximately the size of a thumbnail. Other, larger transformers are used to connect national power grids.
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How Does a Transformer Work?
The first principle of a transformer is that an electrical current passing through a wire creates a magnetic field (this is known as electromagnetism). The second principle is that a changing magnetic field generates a electrical current within a coil of wire. A transformer has two coils. The primary coil has a current that goes through it, which generates a magnetic field that extends to the secondary coil. As the current in the primary coil changes, it causes changes in the magnetic field that the secondary current is exposed to, causing an electrical current to be induced in the secondary coil.
Hypothetically, a transformer is perfectly efficient, but real transformers have certain deviations from that ideal. Some of the electrical current leaks out of the wires, reducing its efficiency. Some of the electricity is lost and dissipates into the core (the windings of the coil), and the surrounding structures. Larger transformers have less of this, which allows them to be more efficient than smaller transformers. Using superconducting wires also can raise the efficiency of a transformer.